COSEWIC Assessment and status report on the Burrowing Owl Athene cunicularia in Canada, 2017

Burrowing Owl

Burrowing Owl
Photo: © Dr. Geoff Holroyd.


COSEWIC assessment and status report on the Burrowing Owl Athene cunicularia in Canada, 2017

COSEWIC Assessment and Status Report on the Blanding’s Turtle

COSEWIC
Committee on the Status
of Endangered Wildlife
in Canada

COSEWIC logo

COSEPAC
Comité sur la situation
des espèces en péril
au Canada

COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:

COSEWIC. 2017. COSEWIC assessment and status report on the Burrowing Owl Athene cunicularia in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xii + 57 pp. (Species at Risk Public Registry website).

Previous report(s):

COSEWIC 2006. COSEWIC assessment and update status report on the Burrowing Owl Athene cunicularia in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 31 pp.

COSEWIC 2000. COSEWIC assessment and update status report the on Burrowing Owl Athene cunicularia in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 35 pp.

Wellicome, T.I. and E.A. Haug. 1995. Second updated COSEWIC status report on the Burrowing Owl Speotyto cunicularia in Canada. Committee on the Status of Endangered Wildlife in Canada. 1-37 pp.

Haug, E.A. and A.B. Didiuk. 1991. Updated COSEWIC status report on the Burrowing Owl Speotyto cunicularia in Canada. Committee on the Status of Endangered Wildlife in Canada. 1-35 pp.

Wedgwood, J.A. 1979. COSEWIC status report on the Burrowing Owl Athene cunicularia in Canada. Committee on the Status of Endangered Wildlife in Canada. 1-90 pp.

COSEWIC would like to acknowledge Geoff Holroyd for writing the status report on the Burrowing Owl (Athene cunicularia) in Canada, prepared under contract with Environment and Climate Change Canada. This report was overseen and edited by Marcel Gahbauer, Co-chair of the COSEWIC Birds Specialist Subcommittee.

COSEWIC Secretariat
c/o Canadian Wildlife Service
Environment Canada
Ottawa, ON
K1A 0H3

Tel.: 819-938-4125
Fax: 819-938-3984
E-mail: COSEWIC E-mail
Website: COSEWIC

Également disponible en français sous le titre Évaluation et Rapport de situation du COSEPAC sur la Chevêche des terriers (Athene cunicularia) au Canada.

Burrowing Owl - Photo courtesy of Dr. Geoff Holroyd.



Burrowing Owl
Athene cunicularia

Burrowing Owls (Athene cunicularia)are small, long-legged predators of the open prairie closely associated with burrowing mammals such as American Badger, Richardson’s Ground Squirrel, Black-tailed Prairie Dog, Coyote, and foxes. Adult Burrowing Owls are intricately coloured with a mix of brown, white, and beige spotting. Juveniles are more richly coloured in dark brown and cream. Adults and young are relatively conspicuous when they are active during the day and at dusk in summer, foraging from elevated mounds and fence posts in open, prairie habitats, and hover hunting. Otherwise they are inconspicuous and easily overlooked for most of the year.

Burrowing Owls were once a common element of the landscape in the Prairies and southern interior of British Columbia. They are now rare throughout their Canadian range, and declining everywhere except in the core of their range in the US. Burrowing Owl is a charismatic flagship species for conservation of native prairie communities.

Burrowing Owls are widely distributed within appropriate habitat in the Americas, from Canada to southern South America. In Canada, they have a disjunct breeding distribution. A small (reintroduced) population breeds in the Thompson-Nicola and Okanagan valleys of southcentral British Columbia, while the main prairie population breeds from southcentral Alberta east through southern Saskatchewan. A small number of reintroduced pairs have reoccupied southwestern Manitoba after being extirpated as a breeding species there for a number of years. In the United States, Burrowing Owls breed from the Great Plains westward, with a disjunct subspecies resident in Florida (A. c. floridana). Canadian Burrowing Owls winter primarily in Mexico and the southwestern United States (e.g., south Texas, New Mexico, Arizona, and California). The breeding range of Burrowing Owls in Canada has shrunk in the past 40 years to less than half of the range occupied in the 1970s, and to only one-third of the range occupied in the early 1900s.

Preferred habitat of Burrowing Owls is open, sparsely vegetated grasslands with burrows excavated by Black-tailed Prairie Dogs, American Badgers, Coyotes, foxes, and ground squirrels. Foraging habitat is generally in and around nesting sites during the day, but at night, owls may forage further afield and in areas with denser grasses and forbs. On the wintering grounds, habitat includes open grasslands, agricultural fields, and scrubland.

Burrowing Owls return to Canadian breeding areas during April and May and nest in existing burrows created by fossorial mammals. In Canada, clutches are initiated in May, with an average of nine eggs (range = 5−14). Typically, a single brood is raised, although pairs that fail may lay a second (smaller) clutch. Family groups remain together until late August, then disperse to individual burrows before migrating southward in September and October.

Data from intensive and extensive Burrowing Owl surveys suggest a continuing significant decrease in density in all areas of prairie Canada over the past 40 years, including a 90% population decline from 1990 to 2000, and further declines from 2005-2015 of 76% in Saskatchewan and 45% in Alberta. In Canada, the current population size can be approximated by considering rate of change in relation to previous estimates. The most recent estimate of population size in 2004 was a minimum of 795 mature individuals: 498 in Saskatchewan, 288 in Alberta, and 9 in British Columbia. Based on rates of decline since 2004, population estimates as of 2015 were 106 in Saskatchewan and 148 in Alberta. In 2015, the BC population of wild owls was 16 and in Manitoba it was zero. Thus, the minimum Canadian population estimate as of 2015 is approximately 270 owls. In the U.S., populations of Burrowing Owls are thought to be stable in the core of the species’ range (i.e., Colorado, New Mexico, Texas), but declining in California, in states along the eastern edge of the species’ range, and in the northern states that border Canada. Though population trends in Mexico are unknown, wintering owl populations have declined in Texas and California, where some of Canada’s breeding population spends the winter.

Historically, the ultimate factor responsible for the decline in Burrowing Owls in Canada was the conversion of grassland to cropland, as well as the fragmentation and degradation of remaining grasslands. However, reductions in prey populations, climate change and severe weather, vehicle collisions, effects from the expansion of renewable energy, and predation may be the biggest current threats to Burrowing Owls.

Factors that limit the Burrowing Owl’s population in Canada are low productivity, low post-fledging survival, low annual survival of juveniles and adults, and high annual dispersal (net emigration to the US and Mexico).

Burrowing Owl has been listed as Endangered under the Species at Risk Act (SARA) since June 2003. Critical habitat for Burrowing Owl has been identified within Grasslands National Park in Saskatchewan. Globally, Burrowing Owl is classified by NatureServe as G4 (apparently secure because of wide distribution, but some cause for concern due to declines). However, the last NatureServe assessment was in April 2004, and therefore does not reflect more recent declines. Provincial NatureServe rankings are S1B in Manitoba and British Columbia, and S2B in Saskatchewan and Alberta. Burrowing Owl is listed as Endangered in Manitoba, Saskatchewan, Alberta, and British Columbia, and as Endangered, Threatened or a Species of Concern in several U.S. states. The most recent COSEWIC designation in April 2017 re-confirmed a status of Endangered (1995, 2000, 2006) for Burrowing Owl in Canada.


Demographic information
Summary items Information
Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines (2011) is being used) 2-3 years
Is there an [observed, inferred, or projected] continuing decline in number of mature individuals? Yes, observed
Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations] Approximately -37% in Saskatchewan and Alberta from 2010 to 2015 (average of provincial trends)
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations]. Observed overall decline of 75.6% in Saskatchewan and 45.4% in Alberta from 2005 to 2015 (overall 64%)
[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations]. Unknown, but expected to continue declining at up to 50-100% based on a threats assessment of very high
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any [10 years, or 3 generations] period, over a time period including both the past and the future. Unknown, but likely >50% given past declines and ongoing threats
Are the causes of the decline a. clearly reversible and b. understood and c. ceased? a. no
b. partially
c. no
Are there extreme fluctuations in number of mature individuals? No
Extent and occupancy information
Summary items Information
Estimated extent of occurrence Approximately 166,000 km2
Index of area of occupancy (IAO)
(Always report 2x2 grid value).
Likely <600 km2
Is the population “severely fragmented” i.e., is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse? a. No b. No
Number of “locations”
See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.(use plausible range to reflect uncertainty if appropriate)
>10
Is there an [observed, inferred, or projected] decline in extent of occurrence? Not within past 10 years, but long-term decline has been observed
Is there an [observed, inferred, or projected] decline in index of area of occupancy? Yes, observed
Is there an [observed, inferred, or projected] decline in number of subpopulations? No
Is there an [observed, inferred, or projected] decline in number of “locations”
See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.?
Unknown
Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat? Yes, observed decline in area and quality of habitat
Are there extreme fluctuations in number of subpopulations? No
Are there extreme fluctuations in number of “locations”
See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.?
No
Are there extreme fluctuations in extent of occurrence? No
Are there extreme fluctuations in index of area of occupancy? No
Number of mature individuals (in each subpopulation)
Subpopulations (give plausible ranges) N Mature Individuals
BC (count as of 2015) 16
AB (minimum estimate as of 2015) 148
SK (minimum estimate as of 2015) 106
MB (count as of 2015) 0
Total >270
Quantitative analysis
Summary items Information
Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years]. Not calculated
Threats (Direct, from highest impact to least, as per IUCN threats calculator)
Summary items Information
Was a threats calculator completed for this species?
Yes, on October 12, 2016 by Geoff Holroyd, Marcel Gahbauer, Dwayne Lepitzki, Pam Sinclair, Troy Wellicome, Ray Poulin, Corey Scobie, Aimee Mitchell, Courtney Conway, Ryan Fisher, Brandy Downey, Joy Stevens, Darcy Henderson, Samantha Fischer, Joanna James.

Overall threat of very high, based on:

  1. Natural system modifications: other ecosystem modifications (high)
  2. Transportation and service corridors: roads and railroads (medium)
  3. Climate change and severe weather: storms and flooding (medium)
  4. Energy production and mining: renewable energy (low-medium)
  5. Invasive & other problematic species: problematic native species (low-medium)
  6. Agriculture: annual and perennial non-timber crops (low)

What additional limiting factors are relevant?
High annual dispersal (net emigration)
Low productivity
Low annual survival
Low post-fledging survival

Rescue effect (Immigration from outside Canada)
Summary items Information
Status of outside population(s) most likely to provide immigrants to Canada. Declining in northern states adjacent to Canadian range
Is immigration known or possible? Yes
Would immigrants be adapted to survive in Canada? Yes
Is there sufficient habitat for immigrants in Canada? Yes
Are conditions deteriorating in Canada?
See Table 3 (Guidelines for modifying status assessment based on rescue effect).
Yes
Are conditions for the source population deteriorating?
See Table 3 (Guidelines for modifying status assessment based on rescue effect).
Likely
Is the Canadian population considered to be a sink?
See Table 3 (Guidelines for modifying status assessment based on rescue effect).
No, source to declining US population due to annual dispersal, with net loss from Canada
Is rescue from outside populations likely? No
Data sensitive species
Summary items Information
Is this a data sensitive species? No
Status
Summary items Information
COSEWIC: Designated Threatened in April 1979. Status re-examined and confirmed in April 1991. Status re-examined and designated Endangered in April 1995. Status re-examined and confirmed in May 2000, April 2006, and April 2017.
Status and reasons for designation
Summary items Information
Status Endangered
Alpha-numeric codes A2bc+4bc
Reasons for designation This grassland owl has suffered ongoing large declines across much of its North American range. The Canadian population was reduced by 90% from 1990 to 2000, and by a further 64% between 2005 and 2015. Most of the remaining individuals are in southern Alberta and Saskatchewan. In recent years small numbers have been counted in British Columbia and Manitoba due largely to captive breeding and release programs. The loss of grassland habitat and suitable burrows has been compounded by a reduction in prey populations, and concurrent increases in predation, vehicle collisions, expansion of renewable energy, and severe weather events.
Applicability of criteria
Summary items Information
Criterion A (Decline in Total Number of Mature Individuals) Qualifies as Endangered under A2bc based on a population size decline of 64% over the past 10 years, and under A4bc given a projected continuing decline due to multiple ongoing threats including reduction in quality of habitat and reduction in area of occupancy.
Criterion B (Small Distribution Range and Decline or Fluctuation) Not applicable, as IAO and EOO both exceed thresholds.
Criterion C (Small and Declining Number of Mature Individuals) Not applicable. Does not meet threshold for Endangered, but qualifies as Threatened under C2a(i) based on ongoing decline in number of mature individuals, and no subpopulation with more than 1000 mature individuals.
Criterion D (Very Small or Restricted Population) Not applicable. Qualifies as Threatened under D1, with a population estimate of ~270 mature individuals.
Criterion E (Quantitative Analysis) Analysis not conducted.

Since the previous status report update (COSEWIC 2006), the number of Burrowing Owls has declined by a further 60%, following a decrease of 90% through the 1990s. The species has become so rare that most monitoring projects have terminated due to the scarcity of sightings. Prairie dog colonies in and near Grasslands National Park in Saskatchewan represent one of the few remaining strongholds for the species, but even there, Burrowing Owls have become scarcer. The ongoing decline appears to be related to low over-winter return rates of owls and low productivity, which in turn is influenced by predation, lack of food, and severe weather events. A tendency toward high dispersal and the existence of vacant habitat in the US may be resulting in net emigration from Canada. In British Columbia, increased captive breeding and release efforts over the past decade have resulted in modest growth of the subpopulation.

A federal recovery strategy for Burrowing Owl was drafted in 2007 and finalized in 2012 (Environment Canada 2012), including identification of critical habitat in and near Grasslands National Park.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.


English name: Burrowing Owl

French name: Chevêche des terriers

Scientific name: Athene cunicularia (Molina)

Between 18 and 20 subspecies of Burrowing Owl have been recognized (Clark et al. 1978; Clark 1997). The only subspecies in Canada is A. c. hypugaea, which ranges from western Canada into Central America (Clark 1997).

The Burrowing Owl is a small, ground-dwelling owl of open habitats, which typically occurs in close association with burrowing mammals. Adults are intricately coloured brown and white, with cream spotting. Juveniles are more richly coloured in dark brown and cream. Adults and young are relatively conspicuous when they are active during the day and at dusk in the summer breeding range. They typically perch on the ground, on mounds, or on low perches (e.g., fence posts). They forage from these locations in open prairie habitats, as well as hover hunting. They fly low to the ground with rapid wingbeats. During the rest of the year Burrowing Owls are inconspicuous and easily overlooked.

The Canadian distribution of Burrowing Owl is split into southern BC and the southern Prairie Provinces, but the species’ range is continuous in the US. Two genetic studies have found no separation within the range of this species in western North America (Korfanta et al. 2005; Macias-Duarte 2011).

The Canadian distribution of Burrowing Owl is highly variable. While they historically had a tendency to occur in loose colonies, they now occur so rarely on the landscape that colonies are relatively rare (Skeel et al. 2001) and most recent surveys in Canada have encountered single pairs isolated from others (Holroyd pers. comm. 2015).

In Canada, Burrowing Owls occur in two distinct areas: the three Prairie Provinces and southern BC. Out of ~4,000 banded owls, only one individual was known to move between these two areas. They also appear to have different wintering ranges (Holroyd et al. 2010). However, no genetic difference was found between the Great Plains and western populations, with two detailed studies concluding that the subspecies is panmictic (Korfanta et al. 2005; Macias-Duarte 2011).

Burrowing Owl was formerly a common inhabitant of open habitats throughout most of the western US and the southern parts of western Canada, but has become rare throughout its Canadian range and is declining everywhere except the core of the species’ range in the native grasslands of Colorado and areas of immediately surrounding states. It is the only species in the genus Athene that occurs in North America. It is a charismatic species that has spearheaded conservation actions to successfully engage landowners on the Canadian prairies in helping to preserve habitat for Burrowing Owl and other grassland species (Kjoss 2016).

Burrowing Owl has an extensive breeding range in western North America (Athene c. hypugaea; Figure 1), and a disjunct (resident) subspecies (A. c. floridana) in Florida. There are also a number of subspecies on various Caribbean islands, in the Pacific Ocean (Isla Clarion, Mexico), as well as in South America (Clark 1997; Figure 2).

The wintering distribution of western North American populations extends from the southwestern US to central Mexico. In the northern portions of the range (including Canada), the species is migratory, while some individuals in the southern part of the North American breeding range (e.g., Mexico, Texas, Oklahoma, California, Arizona, New Mexico) may remain on their breeding sites through the year. Adult and juvenile owls marked in Manitoba, Saskatchewan, and Alberta appear to migrate south through the central Great Plains to winter between southern Texas and central Mexico (James 1992; Hjertaas et al. 1995; Holroyd et al. 2010; Holroyd and Trefry 2011a).

Since 2000, the breeding range of the western Burrowing Owl has not changed from that shown by Wellicome and Holroyd (2001), according to records in eBird (2015).

Figure 1. Breeding range of Burrowing Owls (A. c. hypugaea subspecies) as of 1970 and 1990s in western North America (modified from Wellicome and Holroyd 2001). No published information is available for the historical (early 1900s) range of the owl across North America, nor since 2000, nor for historical distribution in Mexico.
Breeding range of Burrowing Owls as of 1970 and 1990s in western North America
Long description for Figure 1

Map illustrating the extensive breeding ranges of the Burrowing Owl (Athene cunicularia hypugaea subspecies) as of the 1990s and historically (1970) in western North America.

Figure 2. World range of Burrowing Owl (Athene cunicularia; All About Birds 2015).
World  range of Burrowing Owl
Long description for Figure 2

Map illustrating the global distribution of the Burrowing Owl (Athene cunicularia).The wintering distribution of western North American populations extends from the southwestern United States to central Mexico. In the northern portions of the range (including Canada), the species is migratory, while some individuals in the southern part of the North American breeding range (e.g., Mexico, Texas, Oklahoma, California, Arizona, New Mexico) may remain on their breeding sites through the year.

In Canada, Burrowing Owls currently breed regularly in Saskatchewan, Alberta, and the southern interior of British Columbia, occupying only ~50% of the range compared to the 1970s (166,000/330,000 km2) and 37% compared to 1880-1950 (166,000/449,000 km2; Figure 3 ). In British Columbia and Manitoba, Burrowing Owl was extirpated as a breeding species in the early 1980s and 1990s, respectively; more recent breeding in both provinces is the result of reintroduction programs (Dyer 1991; Leupin and Low 2001; Brodie 2010; Brodie pers. comm. 2015; De Smet pers. comm. 2015; Froese pers. comm. 2015).

Figure 3. Change in the Canadian breeding distribution of the Burrowing Owl (COSEWIC 2006). The 2004 distribution was based on intensive search effort. The owls’ 1970−1977 breeding range is based on Wedgwood (1978), and the 1993 range is from Wellicome and Haug (1995). The historical range (1880−1950) is based on a comprehensive literature review of written records from early explorers and naturalists (Wapple 2005), with B.C. portions updated by Surgenor (pers. comm. 2005).
Change in the Canadian breeding distribution  of the Burrowing Owl (COSEWIC 2006)
Long description for Figure 3

Map illustrating the Canadian breeding distribution of the Burrowing Owl historically (1880 to 1950), in 1970 to 1977, in 1993, and in 2004.

Only one pair was confirmed breeding in Manitoba from 2000 to 2005. Since then a small population has established in extreme southwestern Manitoba naturally and was supplemented with release of captive-bred owls. However, no wild pairs nested in Manitoba in 2014 or 2015 (Froese pers. comm. 2015).

The breeding range in Saskatchewan has over time contracted towards the south and west (Figure 3). Burrowing Owls are sparsely distributed in the southern prairie areas, but they no longer breed in many former nesting areas of central (e.g., Saskatoon; Smith 1996) and southeastern Saskatchewan (Wellicome and Holroyd 2001; COSEWIC 2006). Average colony size has also declined over time in Saskatchewan (Skeel et al. 2001).

In Alberta, the species was found historically throughout the Prairie region, north to the edge of the aspen parkland and west to the fescue prairie (Figure 3; Salt and Wilk 1958). In past decades, the species’ range in Alberta has contracted, especially along the western and northern peripheries (Wellicome and Holroyd 2001). Recent northern records of Burrowing Owls near Peace River, Alberta (Trefry and Holroyd 2011) and Wainwright, Alberta (Holroyd and Trefry pers. comms. 2016) are likely anomalous breeding pairs, rather than indicators of a northern extension to their former breeding range.

In BC, Burrowing Owls bred historically near Kamloops, in the Similkameen and Okanagan valleys (Godfrey 1986) and in the Fraser River delta (Campbell et al. 1990). In the interior, colonies of up to six breeding pairs were present in suitable grasslands and sagebrush meadows at the end of the 19th century (Venables 1909). On Lulu Island, in the Fraser Delta, one or two pairs were recorded annually from 1939-1976 (Campbell et al. 1990). Wedgewood (1978) reported records near Creston, Wardner, Revelstoke, Roosville and West Kootenay, all of which Campbell et al. (1990) considered unconfirmed. More recently, releases of captive bred and overwintered young have established breeding pairs in the Thompson, Nicola and Okanagan Valleys (Brodie 2010; Brodie pers. comm. 2015; Chutter 2015).

Although Burrowing Owls are found on Aboriginal lands within the species’ current range, no breeding owls were found during surveys in 2003 on the Blood, Nekaneet, Piapot, and Siksika reserves (although an old nest site was located on Siksika; T. Wellicome unpubl. data). However, in 2005, one nest was found on the Blood Reserve, and one or two were reported from Siksika (COSEWIC 2006). Cardinal (2014) reviewed Aboriginal Traditional Knowledge of Burrowing Owls. This report concluded “Little Aboriginal traditional knowledge is available regarding Burrowing Owls in Canada. While there are nearly one hundred different Aboriginal Nations and organizations whose territories or area of interest overlap with historical Burrowing Owl habitat, ATK was identified for fifteen of them. Of this available ATK, much of it was limited in scope and consisted of recent surveys for individuals and habitat/nesting sites on Reserve lands. Hence, some information was available on population and distribution data but this was largely limited to presence/absence information. Some information was available on cultural significance of Burrowing Owls, though this was restricted to the general role of owls as opposed to identification of any food, social, or ceremonial importance.”

Recent records, including those from eBird (2015), show scattered records as far north as the distribution described by Wellicome and Holroyd (2001) and reported in the 2006 COSEWIC report; this extent of occurrence is approximately 166,000 km2. The actual area of occupancy has likely declined as reflected by a general southward contraction of breeding Burrowing Owls (Macias-Duarte and Conway 2015), but cannot be quantified without extensive surveys that are unlikely to happen (see next section). Given a population estimate of ~270 individuals (135 or fewer pairs), the area of occupancy would be ~540 km2 if each pair is in a separate 2x2 km grid cell, but might be somewhat smaller if multiple pairs are breeding close together.

No recent surveys have been undertaken across Alberta and Saskatchewan because the density of Burrowing Owls is so low and the range so vast that surveys are not practical for this species. Surveys in 2002-03 detected owls at approximately 1 of every 50 survey points (Holroyd and Trefry pers. comms. 2015) and the number of owls has declined since then. Some of the surveys described below (see Population Sizes and Trends) have ended within the past decade due to the low detection of owls. Burrowing Owls are still censused in BC where reintroductions continue and in Grasslands National Park in Saskatchewan.

Burrowing Owls nest in open grassland, such as grazed pastures, prairie (sometimes with small amounts of sagebrush), and the edges of agricultural fields (Poulin et al. 2005). In Canada, Burrowing Owl habitat in Saskatchewan and Alberta is typically flat, treeless prairie, while in British Columbia preferred habitat is plateau and valley grassland (Wellicome and Haug 1995). Another important habitat component for Burrowing Owls is proximity to short to tall grass for (largely nocturnal) foraging. While Burrowing Owls typically restrict their diurnal foraging to the area in the immediate nest vicinity, they appear to range more widely at night, feeding over nearby fields often adjacent to denser vegetation (Haug and Oliphant 1990; Plumpton 1992; Sissons et al. 2001; Sissons 2003). The denser vegetation supports more small mammals while the owls forage at the edges where small mammals are more accessible. On the wintering grounds, habitat includes open grasslands, agricultural fields, and scrubland.

In Canada, nests are in abandoned burrows of various mammals, including Black-tailed Prairie Dog (Cynomys ludovicianus), American Badger (Taxidea taxus), foxes (Vulpes spp.), Striped Skunk (Mephitis mephitis), Coyote (Canis latrans), marmots (Marmota spp.), and Richardson’s Ground Squirrel (Spermophilus richardsonii) (Wellicome and Haug 1995; Wellicome 1997; Poulin et al. 2005), or in artificial nest burrows (De Smet 1997; Wellicome et al. 1997; Leupin and Low 2001). Burrowing Owls typically nest in whichever burrow type with suitable diameter is most common locally. On the Great Plains, Burrowing Owls appear to show a preference for nesting in active prairie dog towns (e.g., Butts and Lewis 1982), and owl abundance may be linked to the local abundance of prairie dogs (Desmond et al. 2000). In Canada, most Burrowing Owls now nest in abandoned badger or Richardson’s Ground Squirrel burrows (Environment Canada 2012). As the owls generally prefer burrows with entrances that are ‘badger-sized’, the owls will sometimes dig with feet and beak to expand ground squirrel burrow entrances to be similar in size to those made by badgers (Poulin et al. 2005). Roost burrows are typically used by males and later by part of the brood when the young are over 3 weeks of age. Roost burrows are typically but not always within sight of the nest burrow. Both types of burrows are described as the owl’s ‘residences’ (Environment Canada 2005).

Burrowing Owls typically spend the day close to their nest burrow and fly further from the burrow area at night to forage (Haug and Oliphant 1990; Marsh et al. 2014; Scobie et al. 2014). Reported mean home range sizes for Burrowing Owls are 2.4 km2 in Saskatchewan (Haug and Oliphant 1990) and 3.7 km2 in Alberta (Sissons 2003). Sissons (2003) showed that Burrowing Owls spend considerable time foraging at night in nearby grassland areas. Home-range size shows a positive correlation to the percentage of surrounding habitat that is under agricultural cultivation, suggesting that larger home ranges are required when higher proportions of land are under cultivation (Haug 1985; Wellicome and Haug 1995). Marsh et al. (2014) cautioned that the habitat types encompassed within home ranges may not reflect their relative importance for prey acquisition. They found that nocturnally foraging Burrowing Owls were most successful at acquiring prey from stubble fields and less along roadways, which had a lower use-value in their home ranges.

Suitable breeding, migration, and wintering habitats have declined in extent and quality over the course of several decades (Telfer 1992; Hjertaas 1997; Warnock and Skeel 2004; Holroyd and Trefry 2011b). Telfer (1992) estimated a loss of 39% of the native grasslands in prairie Canada between 1949 and 1986. Hjertaas and Lyon (1987) estimated a 21% loss of native prairie in Saskatchewan over a 7-year period in the late 1970s and early 1980s. In Manitoba, at least 20% of historical nest sites monitored over a five-year period were destroyed during land cultivation or urban development (Haug and Churchward 1988). Warnock and Skeel (2004) reported that grassland loss, specifically from owl sites in southern Saskatchewan, averaged 6% per year from 1987 to 1993. Overall, 80% of grassland habitats in the three Prairie Provinces had been converted by 1987 (WWFC 1987), and annual habitat loss since then was estimated at 0.6-6.2% per year (Holroyd and Trefry 2011b). All of these studies suggest that the primary loss of habitat occurs through conversion of native grasslands to agricultural crops. The potential sale of Prairie Farm Rehabilitation Administration (PFRA) community pastures in Saskatchewan could result in additional loss of suitable habitat.

In Canada, the loss of grassland habitat has been accompanied by a decline in many species, including a particularly rapid decrease in the abundance of Burrowing Owls. Key components of habitat that are important to Burrowing Owls include fossorial predators such as badgers that prey on ground squirrels and consequently enlarge those burrows to a size suitable for Burrowing Owls. On the prairies, there were indications that Richardson’s Ground Squirrels decreased in some parts of Manitoba (De Smet pers. comm. 2015), Saskatchewan (Schmutz et al. 2001) and Alberta (Kirk and Banasch 1996), but population data are not available at larger scales (Michener and Schmutz 2002). In British Columbia, Howie (1980) identified a reduction in American Badger (T. t. jeffersonii) populations as the main factor responsible for the provincial Burrowing Owl decline. The populations of Burrowing Owl in the four western provinces are now so low that areas of potentially suitable habitat are not currently occupied (Skeel et al. 2001; Burrowing Owl Recovery Team 2004; Holroyd and Trefry 2011b).

Burrowing Owls have a strong association with Black-tailed Prairie Dogs (Klute et al. 2003). Western North America was historically covered by 155.5 million hectares of prairie dog colony habitat. This breeding habitat has now been reduced to only 311,000 hectares, a loss of over 99%. Black-tailed Prairie Dog is considered Threatened in Canada on the basis of its small remnant population in southern Saskatchewan being at risk of disease and effects of increased drought frequency (COSEWIC 2011).

Burrowing Owls are summer residents in the northern portions of their breeding range, including Canada. Some individuals released in British Columbia in captive-breeding reintroduction programs do not migrate, but this is likely an artifact of captive-breeding and release as yearlings. Burrowing Owls arrive on their prairie breeding grounds in April and May, lay an average of nine eggs, typically fledge three to five young, and then begin fall migration in late August or September (Wellicome 1997; Wellicome 2000; Todd et al. 2003). Most pairs are monogamous (Wellicome 2005), although polygyny is occasionally reported (Haug 1985).

Male owls typically defend a nest site and display for prospecting females (Poulin et al. 2011). Both sexes may renovate and maintain the nest burrow, but only females incubate eggs and brood young. Males provision the female with food during the 28-30 day incubation period and while nestlings are brooded (Poulin 2003; Poulin et al. 2011). The nestling period lasts approximately 44 days (Landry 1979), after which time juveniles disperse to nearby satellite burrows (Green 1983; Todd 2001a). Normally only a single brood is raised but a pair may re-nest if the first clutch is lost early in the season (Poulin et al. 2011). Second broods have been recorded in Arizona and one female Burrowing Owl nested twice in the same year, 2003, in Arizona and Saskatchewan (Holroyd et al. 2011).

Estimates of adult apparent survival have ranged from 24% to 40% during a population decline in Manitoba (De Smet 1997), 37% to 51% over six years in Saskatchewan (James et al. 1997), and 47% to 58% in Alberta (unpubl. data cited in Poulin et al. 2011), while Dyer (cited in Poulin et al. 2011) reported a 37% return rate for adults in British Columbia. Juvenile apparent survival rates are lower, but are more difficult to estimate due to the lower site-fidelity of juvenile owls (De Smet 1997; Wellicome et al. 1997). De Smet (1997) measured a 3.5% return rate for juveniles in Manitoba, while Hoyt et al. (2001) found a 6% return rate in Saskatchewan, and Dyer (cited in Poulin et al. 2011) found a 14% return rate for juvenile owls in B.C. Johnson (1997) found a minimum juvenile survival rate of 23% in a non-migratory population in California, but lower juvenile survival rates were noted in Colorado, where only 5% of migratory fledglings were seen the following year (Lutz and Plumpton 1997). Clearly, these return rates underestimate survival rates, given that many adults and juveniles typically disperse from breeding and natal areas (see Dispersal and Migration below). The lack of an accurate measure of adult and juvenile survival rates hampers attempts to accurately predict local population viability (McDonald et al. 2004).

Productivity of Burrowing Owls is highly variable in Canada. A food supplementation experiment clearly showed that in some years food is limiting within the first 3 weeks after hatching and up to 50% of nestlings can die in this time frame (Wellicome 2000; Wellicome et al. 2013).

Juvenile mortality after fledging apparently varies with predation pressure and local food availability. In Saskatchewan, Todd et al. (2003) found that mortality of radio-tagged juveniles during the period between fledging and migration averaged 42% during normal years, but that no tagged juveniles died in a year of high food availability. In Alberta, post-fledging juvenile mortality ranged from 55% during 1995-1996 (n = 21; Clayton and Schmutz 1999) to 39% during 1999-2000 (n = 52; Shyry 2005). In addition, juvenile mortality tended to be higher in relatively fragmented habitat patches (Todd 2001b), suggesting that habitat fragmentation may be negatively affecting juvenile survival in Great Plains habitats (see also Clayton and Schmutz 1999). Generation time is approximately 2-3 years.

Most studies of Burrowing Owl foraging behaviour have noted the flexibility in the species’ diet, depending on time of day, season, and local fluctuations in different prey species (McDonald et al. 2004). On the Canadian prairies, voles (Microtus spp.), mice (Peromyscus spp.), grasshoppers (Acrididae), and beetles are common prey items (Poulin et al. 2011). During summer, Burrowing Owls typically forage during the day around their nest sites for insects, but feed on small mammals in nearby grasslands at night (Schmutz et al. 1991; Sissons et al. 2001; Poulin et al. 2011). During the breeding season in Saskatchewan, over 90% of the prey biomass is composed of small mammals and such prey is typically captured at night (Poulin 2003; Shyry 2005; Poulin and Todd 2006; Marsh et al. 2014; Scobie 2015). A similar ratio of insects to mammals is consumed during the winter in Mexico (Valdez Gomez et al. 2002, 2009).

The degree to which adult and juvenile Burrowing Owls show fidelity to breeding and natal sites is difficult to assess, as re-sightings of banded birds within finite study areas may underestimate dispersal. However, information from stable isotope studies suggests significant dispersal and genetic exchange among neighbouring populations (Duxbury 2004).

In Alberta, observations of individually marked returning juveniles showed that nests were established 300 m to 30 km from their natal sites, with females moving farther than males (J. Schmutz, cited in Poulin et al. 2011). Natal dispersal on the Regina Plain ranged from 0 to 295 km (Wellicome et al. 1997). De Smet (1997) reported that returning juveniles nested 1 to 77 km from their natal sites in Manitoba. Between-year movements of adults were significantly lower. On the Regina Plain, movements ranged from 0−45 km for females, with no dispersal (i.e., 100% site fidelity) shown by males (Wellicome et al. 1997). Adult males in Manitoba moved an average of 3.0 km among years and females moved an average 10.9 km (De Smet 1997). However, the maximum dispersal distance for both juveniles and adults increases with the area of the study sites, indicating that true maxima are even larger than above. Duxbury (2004) estimated average annual dispersal at 400 km with a maximum of 3,500 km based on stable isotope analysis. One female owl that carried a satellite transmitter from southern Alberta bred in Colorado the following year, a dispersal of ~1,000 km (Holroyd and Trefry 2011c).

Burrowing Owls from the Canadian prairies migrate directly south through the Great Plains and winter from south Texas to central Mexico (Holroyd et al. 2010). Burrowing Owls from Alberta and Saskatchewan were followed with VHF telemetry to wintering sites between Houston, Texas and Michoacan, Mexico (Holroyd et al. 2010). A Burrowing Owl with a geolocator wintered in central Mexico (Holroyd and Trefry 2011a). Burrowing Owls from Alberta and Saskatchewan carrying satellite transmitters wintered across central Mexico from Veracruz to Baja (Holroyd and Trefry 2011a,c). Finally, stable isotope analysis of feathers from wintering owls in central Mexico shows some of these owls were in prairie Canada the previous summer (Duxbury 2004). Owls that breed in southern BC primarily overwinter in the Pacific US states from Washington to California (Holroyd et al. 2010; Brodie pers. comm. 2015) with a few records scattered in the lower Fraser Valley and Vancouver Island (Campbell et al. 1990; eBird 2015).

Aside from anecdotal observations of Burrowing Owls being harassed by songbirds (e.g., Martell 1990), there are few observations of interspecific interactions aside from predation events.

Adult and juvenile Burrowing Owls are taken by a wide range of predators, with raptors and badgers being the most common (Wellicome et al. 1997; Todd et al. 2003; McDonald et al. 2004). Predation has been cited as a significant source of mortality in local populations. For example, an entire wintering population on Santa Barbara Island, California was eliminated due to predation by Barn Owls (Tyto alba; Drost and McCluskey 1992). In Alberta and Saskatchewan, avian predation accounted for almost half of all mortality of juvenile owls between the fledging and migration periods (Clayton 1997; Todd 2001a,b). Reintroduction efforts in British Columbia have been hampered by heavy predation from Northern Harriers (Circus cyaneus), Red-tailed Hawks (Buteo jamaicensis), Great Horned Owls (Bubo virginianus), and Coyotes (Leupin and Low 2001). Barn Owls and Short-eared Owls (Asio flammeus) killed Burrowing Owls in winter in Mexico (Holroyd et al. 2003). Badgers have been noted as frequent predators of Burrowing Owls in Saskatchewan (Wellicome et al. 1997), Oregon (Green 1983), and Nebraska (Desmond 1991). Finally, near human habitations, domestic cats and dogs are known to prey on eggs and young (Haug 1985; Millsap and Bear 1988; Sleno 2000).

No quantitative sampling has been undertaken to determine the current number of Burrowing Owls in Canada. In prairie Canada, the owls are too thinly dispersed to be effectively surveyed. Previous COSEWIC status reports have given population estimates of Burrowing Owls, but they were also not based on quantitative sampling, and Recovery Team members expressed concerns that they did not reflect the more rapid declines shown by systematic localized surveys. Nevertheless, in the absence of more quantitative data, the estimated population cited in the 2006 report was used as a baseline for estimating the current population, factoring in the rate of decline in areas that have received monitoring over the past decade.

Estimates of Burrowing Owl population trends for the breeding season come from a variety of sources including: 1) large-scale Breeding Bird Surveys (BBS) done by volunteers on designated routes in Canada and the United States: 2) surveys of landowners participating in Operation Burrowing Owl in Saskatchewan and Operation Grassland Community in Alberta; and 3) surveys done by Burrowing Owl researchers on the Regina Plain, Grasslands National Park, and other research sites in the prairie provinces. Given the differences in methodology, scale, and observer effort among these surveys, the three survey types have different strengths and weaknesses. While the BBS and landowner surveys give results on the broadest scales, they are also more prone to sampling error. Dedicated Burrowing Owl surveys done by biologists may give more accurate results, but are necessarily restricted to much smaller areas. Taken together, however, these surveys likely provide a relatively robust representation of the long-term population size and trends of Burrowing Owls in Canada.

In the northern portion of their wintering range, Burrowing Owls occur within the area of some Christmas Bird Counts (CBCs). CBCs are done throughout North America and are one-day, fixed-radius surveys conducted each year between mid-December and early January.

In Canada, previous COSEWIC status reports on Burrowing Owls reported population sizes of 2000 pairs in 1977 (Wedgwood 1978), 2540 pairs in 1991 (Haug and Didiuk 1991), 1010-1685 pairs in 1995 (Wellicome and Haug 1995) and 795 adult individuals (i.e., <400 pairs) in 2004, comprising 498 individuals in Saskatchewan, 288 individuals in Alberta and 9 individuals in British Columbia (Burrowing Owl Recovery Team 2004). The 2004 estimate likely underestimated the total Canadian population, as relatively large areas of potentially suitable habitat in Alberta and Saskatchewan were not surveyed; the actual population may have been as high as 1600 individuals (Burrowing Owl Recovery Team 2004). However, some local populations in 2004 were as much as 73% higher than the previous year (Todd pers. comm. 2015), casting doubt on the validity of the higher end of the range. It should be stressed that each of the COSEWIC status reports used different methods to estimate population sizes, thereby complicating long-term trend analysis. No recent broad-scale censuses have been undertaken, but more recent population numbers can be estimated from trends in local population surveys (see Summary of breeding season surveys below).

Burrowing Owls are seen on too few Canadian Breeding Bird Survey routes to generate meaningful population trends (Sauer et al. 2014). However, recent trend data from dedicated Burrowing Owl surveys in Canada show a clear decline in the number of owls since the late 1980s (see Summary of breeding season surveys below).

Fluctuations in most samples, shown below, are minor compared to the overall declining trend. The lone exception is in BC, where the population of adult individuals reflects the increased intensity of the captive breeding and release programs.

Data from Manitoba show a decline from 76 nests in 1982 to 0 nests in 1997 (De Smet 1997, Figure 4 ), and only one nest between 2000 and 2005. Since 2006, up to 13 pairs have been confirmed breeding in Manitoba but no nests were documented in 2014 or 2015 (Froese pers. comm. 2015). While it may be too early to consider the Burrowing Owl extirpated in Manitoba, it is almost certainly only an irregular breeder now in the province (probably <10 pairs).

Figure 4. Trend in the number of pairs of Burrowing Owls found nesting in Manitoba from 1982 to 2015.
Trend  in the number of pairs of Burrowing Owls found nesting in Manitoba
Photo: © updated from De Smet 1997; De Smet, pers. comm., and Froese, pers. comm. 2015
Long description for Figure 4

Chart illustrating the trend in the number of pairs of Burrowing Owls found nesting in Manitoba from 1982 to 2015.

In Saskatchewan, surveys done by Operation Burrowing Owl cover a large proportion of the historical range of the species in the province. The surveys are based on the landowner members of OBO, which have remained relatively constant. However, the survey includes only data from participating landowners and should consequently be viewed as an approximation of the actual population trend in the province.

The number of Burrowing Owls reported by private landowners enrolled in Operation Burrowing Owl in Saskatchewan has declined significantly, from an estimate of around 1000 breeding pairs in the late 1980s to fewer than 100 pairs since 2000 (Figure 5 ).

Research done on the Regina Plain monitored the population status and breeding success of Burrowing Owls from 1987 to 2007. The projects occurred on ever-enlarging study areas. The long-term population trend on the Regina Plain shows a significant decline in numbers from 1987 to 1999, and low numbers of breeding pairs since that time (Figure 6 ). Surveys have been discontinued in the Regina Plain and more recent records are not currently available (Wellicome and Poulin pers. comms. 2015).

Finally, in the west block of Grasslands National Park, including the adjoining Dixon ranch, the number of nesting pairs increased from 1998 to 2005 then declined (Figure 7 ). Breeding success in Grasslands National Park varied considerably among years, with a mean of between 0.9 and 4.5 young produced per nesting attempt (Figure 8 ). Such annual variation is typical, but the overall reproductive success of Burrowing Owls in Grasslands National Park was slightly lower in recent years than that recorded in Great Plains states in the US (McDonald et al. 2004). The surveys in Grasslands National Park began after the large decline experienced elsewhere in the 1990s.

In summary, the various data sets from Saskatchewan suggest a significant long-term province-wide decline in the number of Burrowing Owls.

Figure 5. Burrowing Owl population trend at Operation Burrowing Owl (OBO) sites in Saskatchewan between 1987 and 2015; plotted are number of pairs reported by OBO members, estimated number of pairs with a correction for lower observation effort, and number of OBO members.
Burrowing  Owl population trend at Operation Burrowing Owl (OBO) sites in Saskatchewan
Photo: © Burrows, pers. comm. 2015
Long description for Figure 5

Chart illustrating the trend in the Burrowing Owl population at Operation Burrowing Owl (OBO) sites in Saskatchewan between 1987 and 2015. Plots are shown for the number of pairs reported by OBO members, the estimated number of pairs with a correction for lower observation effort, and the number of OBO members.

Figure 6. Trends in the number of Burrowing Owls found during surveys on the Regina Plain area in southcentral Saskatchewan, 1987-2011. The study areas originally surveyed since 1987 (James et al. 1979) and since 1994 (Wellicome 2000) are geographic subsets, wholly contained within the larger study area surveyed since 1997 (Poulin 2003 and Todd 2001a, respectively). Limited or no surveys were conducted from 2011 to 2015.
Trends  in the number of Burrowing Owls found during surveys on the Regina Plain area
Long description for Figure 6

Chart illustrating trends in the number of Burrowing Owls found during surveys on the Regina Plain area in southcentral Saskatchewan, from 1987 to 2011.

Figure 7. Number of breeding pairs at Grasslands National Park including Dixon’s ranch, Saskatchewan.
Number  of breeding pairs at Grasslands National Park including Dixon’s ranch,  Saskatchewan
Photo: © Holroyd and Trefry, pers. comms. 2015
Long description for Figure 7

Chart illustrating the trend in the number of breeding pairs of Burrowing Owls at Grasslands National Park including Dixon’s ranch, Saskatchewan, from 1998 to 2015.

Figure 8. Productivity of Burrowing Owls at Grasslands National Park including Dixon’s ranch, Saskatchewan.
Productivity  of Burrowing Owls at Grasslands National Park including Dixon’s ranch,  Saskatchewan
Photo: © Holroyd and Trefry pers. comms. 2015
Long description for Figure 8

Chart illustrating the trend in the productivity of Burrowing Owls at Grasslands National Park including Dixon’s ranch, Saskatchewan, from 1998 to 2015.

In Alberta, standardized surveys were conducted from the early 1990s to 2004 near Hanna (104 quarter sections) and Brooks (128 quarter sections), over areas that contain large blocks of suitable habitat (Wellicome 1997; Scobie 2002). In the Hanna blocks, the density of Burrowing Owl nests decreased from a high of >30 per 100 km2 in 1991 to <2 per 100 km2 since 2001 (Figure 9 ). In the Brooks surveys, the decline was less dramatic, down to only 5 nests per 100 km2 in 2002 and 2004, and 2 per 100 km2 in 2007 (Figure 10 ). On a larger scale, data from Operation Grassland Community in Alberta also show a long-term negative trend from 1991 to 1999, an increase in 2004 that was at least partially due to expanded survey participation, and then a continuing decline of 40% from 57 pairs in 2006 to 34 pairs in 2014 (Figure 11). Taken together, the standardized surveys and OGC data from Alberta suggest large declines in the abundance of breeding Burrowing Owls in the province.

Figure 9. Trend in the number of nests/100 km2 on survey blocks near Hanna, Alberta. The negative trend is statistically significant (Rs = - 0.89, P = 0.01, n = 9); the block has not been surveyed since 2003.
Trend  in the number of nests/100 square km on survey blocks near Hanna, Alberta
Photo: © Shyry et al. 2001, COSEWIC 2006
Long description for Figure 9

Chart illustrating the trend in the number of Burrowing Owl nests per 100 square kilometres on survey blocks near Hanna, Alberta, from 1989 to 2003.

Figure 10. Trend in the number of nests/100 km2 on survey blocks near Brooks, Alberta. Note that surveys were not performed in 1996 and 2003, and that an incomplete survey was done in 1993 (Shyry et al. 2001, Russell 2002 and COSEWIC 2006). The block was resurveyed in 2007 and the density of owls was half that of 2004; it has not been surveyed since.
Trend  in the number of nests/100 square km on survey blocks near Brooks,  Alberta
Long description for Figure 10

Chart illustrating the trend in the number of Burrowing Owl nests per 100 square kilometres on survey blocks near Brooks, Alberta, from 1993 to 2007, with exception of 1996, 2003, 2005, and 2006.

Figure 11. Trend in the number of Burrowing Owl pairs reported by Operation Grassland Community landholders and number of OGC members in Alberta between 1989 and 2014.
Trend  in the number of Burrowing Owl pairs and number of OGC members in Alberta
Photo: © Grisley pers. comm. 2015
Long description for Figure 11

Chart illustrating trends in the number of Burrowing Owl pairs reported by Operation Grassland Community landholders and the number of OGC members in Alberta between 1989 and 2014.

Before 1940, breeding populations of Burrowing Owls occurred in the Okanagan and Similkameen valleys and near Kamloops (Campbell et al. 1990). From 1940 to 1979, breeding Burrowing Owls were reported intermittently from only four areas (Cannings et al. 1987; Campbell et al. 1990). Twenty breeding records for the Okanagan Valley exist between 1897 and 1928, but only three from 1928 to 1970 (Cannings et al. 1987). In the Fraser River Delta, on Lulu Island, one or two pairs nested most years from 1939 to 1976 (Campbell et al. 1990). Single owls were recorded near the Boundary Bay airport in 1984, but no breeding records were observed (Campbell et al. 1990).

Burrowing Owls were extirpated in British Columbia sometime in the 1980s (Surgenor pers. comm. 2005). Efforts aimed at re-establishing a viable population in the province started with the release of captive-raised owls in the Thompson-Nicola region in 1983 and the release of owl families transplanted from Washington to the south Okanagan Valley from 1983 to 1988 (Dyer 1991). The program has succeeded in establishing small numbers of captive-raised birds that breed and migrate; as of 2012, 25 individual wild owls had been found in surveys in southern British Columbia (Figure 12 ). Efforts to increase the number of captive-raised and released owls have resulted in up to 257 owls (2011) released annually (Brodie pers. comm. 2015). The increasing number of returning owls indicates some success towards the goal of re-establishing a self-sustaining breeding population in British Columbia, although the fate of the majority of the released owls remains unknown.

Figure 12. Number of wild owls returning in the spring in southern BC, 1992-2014.
Number  of wild owls returning in the spring in southern BC, 1992-2014
Long description for Figure 12

Chart illustrating the trend in the number of wild Burrowing Owls returning in the spring in southern British Columbia, from 1992 to 2014.

Data from the landowner surveys in the Prairie Provinces discussed above suggest a decline throughout the 1990s from about 1315 pairs (MB 75; SK 1000; AB 240) to 125 pairs (0, 100, 25), a decadal decline of about 91%. Over the past decade (2005-2015) the decline based on the same data sources abated to 76% in Saskatchewan (90 pairs in 2005 vs. 22 in 2015, an annual rate of decline of 13.1%) and 45% in Alberta (55 pairs in 2005 vs. 30 in 2015, an annual rate of decline of 5.9%), for an overall rate of decline in these two provinces of 64% over 10 years. The decline in the number of pairs in monitored portion of Grasslands National Park was more severe at 81% from 2005 (64 pairs) to 2015 (12 pairs). If the whole Canadian prairie population has followed these trends, then these numbers lead to a conclusion that Burrowing Owls are at risk of disappearing from prairie Canada.

COSEWIC (2006) estimated a minimum Canadian population of 795 Burrowing Owls in 2004 (498 in Saskatchewan, 288 in Alberta, and 9 in British Columbia). Based on the decadal trends above, estimates as of 2015 would be 106 in Saskatchewan and 148 in Alberta, recognizing that the actual number may be somewhat larger based on uncertainty regarding the 2004 estimates, but almost certainly far less than double. In 2015 the British Columbia population was counted as 16 (Brodie pers. comm. 2015), and in Manitoba there were none, for a minimum total of 270.

Analysis of the long-term trend in the number of Burrowing Owls seen on CBCs in Texas (where some Canadian owls winter) showed a statistically significant decline from 1960 to 2004 (see Figure 13 ; Spearman Rank Correlation Rs = -0.42, n = 43, P < 0.01; COSEWIC 2006). This negative trend has since increased (2005-2014, Rs = -0.80, n = 10, P < 0.01). Similar analysis of CBC data from California, where B.C. owls are thought to winter, shows a strong, significant decline from 1960 to 2003 (Figure 14 ; Rs = -0.66, n = 43, P < 0.001; COSEWIC 2006). This negative trend continued in the last 10 years (2005-2014, Rs = -0.56, n = 10, P < 0.01). However, these data must be interpreted with caution as wintering Burrowing Owls in Texas and California are largely of unknown origin (i.e., it is unclear to what extent owls from the Canadian prairies winter in those two states, and CBC data would include resident owls).

Figure 13. Pattern of abundance (number seen per survey party-hour) of Burrowing Owls seen on Christmas Bird Counts in Texas, 1955-2014.
Pattern  of abundance (number seen per survey party-hour) of Burrowing Owls seen on  Christmas Bird Counts in Texas
Photo: © National Audubon Society 2016
Long description for Figure 13

Chart illustrating the pattern of abundance (number seen per survey party-hour) of Burrowing Owls seen on Christmas Bird Counts in Texas, from 1955 to 2014.

Figure 14. Pattern of abundance (number seen per survey party-hour) of Burrowing Owls seen on Christmas Bird Counts in California, 1955-2014.
Pattern of abundance
Photo: © National Audubon Society 2016
Long description for Figure 14

Chart illustrating the pattern of abundance (number seen per survey party-hour) of Burrowing Owls seen on Christmas Bird Counts in California, from 1955 to 2014.

Burrowing Owls that breed in Canada migrate into the US and Mexico for the winter. Annual dispersal rates are high. Based on stable isotope analysis of feathers, Duxbury (2004) determined that 42.5% of Burrowing Owls breeding in Canada in a given year were in the US or Mexico during the previous breeding season, with an average annual dispersal of 619 km. Conversely, 40% of owls breeding in Montana were in Canada the previous year. Thus, Duxbury (2004) demonstrated that the Burrowing Owl has high rates of dispersal across the international border. One dramatic example of intra-year dispersal of a Burrowing Owl has been published (Holroyd et al. 2011). A female owl bred in Tucson, Arizona and southern Saskatchewan in the same year, raising two broods of young with two males, 1850 km apart. An example of inter-year dispersal was provided by a female owl outfitted with a satellite transmitter that bred in southern Alberta one year and in Colorado the following year, approximately 1000 km apart (Holroyd and Trefry 2011c). Although there is evidence of Burrowing Owls emigrating from the US, rescue is considered unlikely given the declining population throughout most of the species’ range and ongoing threats to habitat within its Canadian range.

The decline of Burrowing Owls in Canada is a function of multiple threats. The Burrowing Owl recovery strategy identifies the following factors: habitat modification, decreased availability of prey, increased predation, inclement weather, vehicles, environmental contaminants, and loss of burrows (Environment Canada 2012). Threats are described below and summarized in Appendix 1 based on a modified version of the IUCN-CMP (World Conservation Union-Conservation Measures Partnership) unified threats classification system (COSEWIC 2014), which resulted in an overall score for Burrowing Owl of very high.

Most Burrowing Owls are exposed to areas where prey availability and condition is affected by use of rodenticides and insecticides. Although the evidence is thus far only correlative, it appears that pesticides may affect reproductive success and survival by significantly decreasing prey abundance. For example, offspring production decreased by up to 83% following the application of carbaryl and carbofuran around Burrowing Owl nest burrows (James and Fox 1987). Strychnine-treated grains (used for rodent control) and carbofuran-based insecticides remain widely used in the United States and Mexico and may pose a threat to the Canadian population of Burrowing Owls during migration and on the wintering grounds (McDonald et al. 2004; Holroyd pers. comm. 2015).

An additional potential threat in farmland is from annual crops that are treated with neonicotinoids that can reduce insect abundance that could reduce food supply for nesting Burrowing Owls. Mineau and Whiteside (2013) suggested that pesticides may be responsible for declines in bird populations inhabiting agricultural areas. Mineau and Palmer (2013) stated that the effects of neonicotinoids, which are used on 11 million ha of cropland across prairie Canada (Main et al. 2014), occur over watershed and regional scales, not just at the level of individual farms. In Europe where more research on the impacts of neonicotinoids has been published, the European Food Safety Authority determined they pose unacceptable risks to insects (Goulson 2014) and concentrations were correlated with declines of farmland birds (Gibbons et al. 2014; Hallmann et al. 2014). While the impact of neonicotinoids on invertebrate abundance has been demonstrated (EASAC 2015), effects on Burrowing Owl prey and productivity are at this point speculative.

Another pesticide threat to prairie ecosystems is doramectin, an insecticide that is given to livestock to treat parasites (Olson pers. comm. 2015). Floate et al. (2008) demonstrated that doramectin inhibited insect use of cattle dung for 16 weeks after livestock treatment. Doramectin is a member of the group of insecticides known as avermectins. Suarez et al. (2009) determined that insect abundance in treated dung was 50-75% less than in untreated dung. Whipple (2011) found 85% fewer dung beetles on a pasture with treated cattle than a comparable pasture with untreated cattle. Although Floate et al. (2008) concluded that dung beetles were not common in the diet of burrowing owls, this could be because the owl diet samples were collected in areas where doramectin was used. The impact of avermectins on prairie insect life is not well quantified (Olson pers. comm. 2015) and its potential effect on the diet of Burrowing Owls is unknown but a possible threat.

An indirect impact of pesticides, specifically strychnine, is the loss of fossorial mammals due to direct and indirect poisoning (Proulx 2014); this in turn reduces the availability of suitable nesting burrows for Burrowing Owls (Environment Canada 2012).

Undergrazing can also make otherwise potentially suitable habitat unattractive (Holroyd pers. comm. 2015). Burrowing Owl nest sites are often in native grasslands grazed by domestic livestock at higher than average stocking rates, resulting in higher than average bare ground exposure (Hjertaas and Lyon 1987; Marsh et al. 2014). It is not clear whether taller vegetation or denser litter decreases prey availability, increases abundance of nest predators, decreases foraging efficiency, or decreases effective predator vigilance by the owls themselves. Grasslands protected from grazing for prolonged periods of time become unattractive to Burrowing Owls, as has been observed at Grasslands National Park (Holroyd pers. comm. 2015). Effects of invasive plants on Burrowing Owls are not well documented, but may also be a concern if they reduce bare ground cover (Holroyd pers. comm. 2015).

Overall, natural system modifications through a combination of declining prey availability and reduced habitat suitability is likely the greatest current threat to Burrowing Owls.

Although poorly quantified, collisions with vehicles are thought to be an important source of mortality for adult and juvenile Burrowing Owls. Owls often forage near roads where grass conditions are optimal for small rodents and insects, and are thus susceptible to collision with vehicles. Clayton and Schmutz (1999) found that approximately 31% of all known Burrowing Owl fatalities on the Regina Plain, Saskatchewan, were due to collisions with vehicles. In Saskatchewan, 15% of known juvenile mortalities, during the post-fledging/pre-migration period, were attributed to collisions with vehicles (Todd et al. 2003). D. Wiggins found two dead adult Burrowing Owls on a single morning on small, secondary roads in the Oklahoma panhandle in May 2005 (COSEWIC 2006).

Droughts, temperature extremes, storms, and flooding are all part of the existing prairie environment. The degree to which these factors affect nesting and survival of Burrowing Owls is not fully known. However, Fisher et al. (2015) found that annual productivity varied inversely with breeding season precipitation, contributing to a decline in productivity of 12% from 1960 to 2012; they concluded that extreme rainfall during the breeding season reduces reproductive success of Burrowing Owls. The warming of the planet (Blunden and Arndt 2016) and specifically the Great Plains of Canada (Whitewood et al. 2016) and United States (Crouch et al. 2016) and the owl’s Mexican winter range (Pascual Ramírez et al. 2016) is ongoing, and precipitation in these regions has generally increased and is expected to continue to do so.

There are no published studies of the effect of energy production and mining on Burrowing Owls. However, oil and gas drilling occur within the Canadian breeding range, as do potash and gravel mining. Regulation of these activities to mitigate for potential effects on Burrowing Owls likely results in a negligible effect on the overall population. Of potentially greater concern is proposed expansion of wind and solar energy production over the next 10-15 years, especially in Alberta, but also through many other parts of the breeding, wintering, and migration range. While habitat fragmentation and loss can be mitigated through careful siting, cumulative effects of mortality from collision with wind turbines may be significant for this species (Smallwood et al. 2007).

Predation by raptors and mammals is recognized as the main cause of adult and juvenile mortality on Canadian breeding grounds (Wellicome and Haug 1995; Leupin and Low 2001; Todd et al. 2003; Shyry 2005). Avian predation was the primary cause of mortality in a study of Burrowing Owl survival in winter in Texas and central Mexico (Holroyd and Trefry pers. comms. 2015). Over a two-year study in Saskatchewan, Todd (2001a,b) found that out of 25 young which died of known causes, 15 (60%) were depredated, mostly by larger birds. The high losses to predators were attributed to a combination of habitat fragmentation and reduced availability of mammalian prey (principally Microtus voles; Todd 2001a,b).

Avian predators of Burrowing Owls have increased due to human activity. Shelterbelts, outbuildings, and trees have provided nest sites for avian predators on native prairie where none existed before (Houston and Bechard 1983; Schmutz et al. 1984; Schmutz 1987; Houston et al. 1998).

Past and ongoing predator control actions affect Burrowing Owl nest success and survival. Historically the elimination of Wolves (Canis lupus) and Grizzly Bears (Ursus arctos) from the prairies allowed smaller predators such as Coyote, Striped Skunk and Raccoon (Procyon lotor) to increase (Wellicome and Haug 1995). Red Fox (Vulpes vulpes) has also expanded into the prairies (Kamler and Ballard 2002); this species has had negative impacts on a wide variety of waterfowl, grouse and other birds in North America (Sargeant et al. 1984; Johnson et al. 1989; Lewis et al. 1999). These species are Burrowing Owl nest predators, as are American Badgers. Feral cats may also prey upon Burrowing Owls on occasion (Sleno 2000), although this is not likely a substantial concern. The provision of artificial nest burrows has been shown to decrease nest predation (Henny and Blus 1981; Olenick 1990; De Smet 1997; Wellicome 2000).

Historically, the ultimate threat to viable populations of Burrowing Owls is thought to have been the conversion and degradation of habitat (Wellicome and Haug 1995; Clayton and Schmutz 1999; Poulin et al. 2011). Telfer (1992) reported a 39% decline in unimproved pastureland between 1946 and 1986 in areas of the Prairie Provinces, while dramatic losses of native grasslands have been reported in Manitoba (99% of both tall and mixed grass prairie), Saskatchewan (81% of mixed grass prairie), Alberta (61% of mixed grass prairie), and the western and central U.S. Great Plains (Samson and Knopf 1994). In Manitoba, at least 20% of historical nest sites recorded over a five-year period were destroyed during land cultivation or urban development (Haug and Churchward 1988). Hjertaas and Lyon (1987) estimated a 21% loss of native prairie in Saskatchewan over a 7-year period in the late 1970s and early 1980s. Warnock and Skeel (2004) reported that grassland loss, specifically from owl sites in southern Saskatchewan, averaged 6% per year from 1987 to 1993. Overall, 80% of grassland habitats in the three Prairie Provinces had been converted by 1987 (WWFC 1987). Since then annual habitat loss has been estimated at between 0.6-6.2% per year (Holroyd and Trefry 2011b). These losses of native grassland are mirrored in the US (Klute et al. 2004; McDonald et al. 2014). All of these studies suggest that the primary loss of habitat occurs through conversion of native grasslands to agricultural crops.

Although the loss of grassland is significant, the direct impact on the population of Burrowing Owls is not obvious. While grassland loss in Saskatchewan from 1987 to 1993 averaged 6% per year, the number of Burrowing Owls reported by Operation Burrowing Owl landowners declined 22% per year (Warnock and Skeel 2004). Holroyd and Trefry (2011b) concluded that the decline of Burrowing Owl population in prairie Canada was occurring faster than the rate of land conversion; consequently land conversion was not the prime factor driving population declines.

Along with conversion to cultivation, fragmentation of native prairie has increased. In the Regina Plain, Saskatchewan and Special Areas in central Alberta, juvenile Burrowing Owls remain closer to their natal burrow in small prairie fragments than on larger grassland patches, but whether this has an effect on their survival is not known (Clayton and Schmutz 1999; Todd et al. 2003).

The impact of agriculture on suitable habitats on migration routes and in winter in the US and Mexico is poorly understood. Burrowing Owls migrating to and from Canada would have used prairie dog colonies and must have been affected by this huge loss of habitat. Increases in agricultural use of grasslands in Chihuahua, Mexico will affect Burrowing Owls (Pool 2014). In winter in south Texas and Mexico, Burrowing Owls occupy a wide variety of habitats beyond just grassland, and they do not always roost in burrows (Holroyd et al. 2010). Some occupied habitats are intensively cultivated fields where Burrowing Owl weights and survival appear high (Holroyd and Trefry pers. comms. 2015). Populations of Burrowing Owls in irrigated cropland in southern California are the densest in North America, but are also declining (Klute et al. 2003; DeSante et al. 2007).

Typically Burrowing Owls fare well where there is grazing, as shorter vegetation facilitates effective hunting. All Burrowing Owls that nest in PFRA pastures are potentially threatened by loss of grazing livestock and changes in grazing rates due to the transfer of ownership and management of these pastures. If these pastures are converted to cultivated crop, the owls will have reduced access to foraging areas and burrows for nesting.

High nestling mortality due to low prey availability is an important factor limiting burrowing owls, but it is unclear which factors influence this threat the most. The intensity of grazing on native grasslands may be among the causes, but no studies have specifically addressed this issue.

Overall, while agriculture has no doubt contributed significantly to past declines in Burrowing Owl populations, current practices likely have a low impact due to the reduced rate of habitat conversion and the neutral or positive effects of grazing.

Threats from residential and commercial development (category 1) were considered negligible, given minimal additional urbanization expected within Burrowing Owl range over the next decade. There have been previous losses of Burrowing Owls in relation to urbanization, most notably Moose Jaw, Saskatchewan, where pairs nested at the town fairgrounds, on the golf course and elsewhere, but have become extirpated despite a conservation plan approved by city council in 2002 (City of Moose Jaw 2002). One or two pairs nesting on Lulu Island BC (now the city of Richmond) may also have been displaced by urbanization. However, Trulio (1997) describes successful nesting of Burrowing Owls in urban areas south of San Francisco, California, and pairs also nest in and appear to prosper in other southern US cities (e.g., Tucson, Arizona and Las Cruces, New Mexico; Holroyd pers. comm. 2015). Barclay et al. (2007) provide extensive literature on the biology of Burrowing Owls in urban and other developed habitats (e.g., airports) in California. Thus is it not clear that urbanization itself is harmful to owls.

Human intrusion and disturbance (category 6) is considered negligible, as Burrowing Owls are generally tolerant of minor human disturbance around nest sites. Each year, researchers visit burrowing owl nests in prairie Canada and in BC. Currently, research includes attaching satellite transmitters to adult owls and monitoring owl occupancy and productivity in Grasslands National Park and in BC.

While indirect effects of pollution (described above under category 7) are likely significant for Burrowing Owls, there may also be some direct effects (category 9; Fox et al. 1989; Gervais et al. 2003), but these are considered to be negligible. While ingestion of prey killed by rodenticides (e.g., strychnine) has potential to cause direct mortality of adult and juvenile owls and to decrease breeding success (Butts 1973; Sheffield 1997), James et al. (1990) concluded there were no detrimental effects on Burrowing Owls when strychnine was applied to grain as directed by manufacturers. Heavy use of insecticides and herbicides near Burrowing Owl foraging and roosting areas has been observed (but not quantified) on the wintering grounds in Mexico (Holroyd and Trefry pers. comms. 2015). In California, samples of Burrowing Owl eggs show varying levels of DDE contamination among years, with significant negative effects on reproductive success during years of poor food availability (Gervais and Anthony 2003).

Scobie et al. (2014) found that Burrowing Owls avoided roads with vehicle speeds >80 km/h. They speculated that road noise interfered with predator detection and intraspecific communication of danger, but it is unlikely that the effect on the population is more than negligible.

Biological resource use (category 5) and geological events (category 10) are not considered to pose any threats to Burrowing Owls. In many areas of their range, Burrowing Owls historically were often victims of shooting programs aimed at prairie dogs (James and Espie 1997). Even when such shooting is not directed at owls, they can be shot accidently (Woodard 2002). However, Burrowing Owls are currently so rare in Canada that shooting is not likely an ongoing concern.

Burrowing Owls have high potential productivity but low annual survival, and in recent decades large numbers of young have been produced only rarely (Wellicome 2000; Environment Canada 2012; Wellicome et al. 2013; Wellicome et al. 2014). Mortality of young and adults also affects Burrowing Owl population viability (De Smet 1997, Clayton and Schmutz 1999, King and Belthoff 2001). Population stability is affected by dispersal, emigration, and immigration (Koenig 2016). These features are discussed in this section.

In Canada, Burrowing Owls are at the northern edge of their range, and typically have a large clutch size. Wellicome (2000) used artificial nest boxes to determine that the average clutch size was nine eggs with 90% hatching success. However, productivity is frequently only three to five young per successful nesting attempt. The year 1997 was an exception, with eight young per successful nest due to high populations of meadow voles. After excluding flooding or predation of whole broods, he found that 96% (169 of 176) of mortalities of individual nestlings within broods was due to food shortages. The Burrowing Owl appears adapted for a boom-bust life history dependent on abundant food supply. Losses of younger nestlings were due to starvation and cannibalism in the first three weeks after hatching (Wellicome 2000), which occurred during particularly rainy periods (Fisher et al. 2015). Factors reducing reproductive success may thus be limiting Burrowing Owls in Canada.

Nest failures are another limiting factor. Complete nest losses occur due to nest predation, wet weather, and adult mortality (see details in Threats). In Manitoba, from 1987 to 1995, 39% of nest attempts (78 of 200) failed (De Smet 1997). From 2003-2006 across Alberta and Saskatchewan, 15% to 27% of nest attempts failed (T. Wellicome unpubl. data quoted in Environment Canada 2012). De Smet (1997) and Todd et al. (2003) found that local populations increased in the year following high fledging success.

Post-fledging survival (from fledging to migration) is typically low. It was 45-48% in 1995-1996 (Clayton and Schmutz 1999), 55% from 1998-2000% (Todd et al. 2003), and 34% in 1999-2000 (Shyry 2005) in three studies of prairie populations, and was 47% in 2005 and 79% in 2006 in British Columbia (Mitchell 2008). Post-fledging survival may be greatly influenced by prey availability; for example, it was 100% for a prairie population in 1997 during a peak in the vole cycle (Poulin et al. 2001).

In contrast, adult survival during the breeding season is relatively high: 83% for males tracked with telemetry (Sissons 2003), 88-100% for females and 94-100% for males based on resightings (T. Wellicome unpubl. data cited in Environment Canada 2012).

Nothing is known about survival during the autumn and spring migrations. In winter, telemetry-based studies in south Texas and central Mexico estimated overwinter survival between 70 and 83% (Holroyd and Trefry pers. comms. 2015).

Mortality of young and adults also affects Burrowing Owl population viability (De Smet 1997; Clayton and Schmutz 1999; King and Belthoff 2001). In Saskatchewan, following years with relatively poor juvenile survival, the local breeding population decreased by 11-48%, while years of high juvenile survival were followed by a population increase as well as relatively strong juvenile recruitment into the breeding population (Todd et al. 2003). The close correlation between nesting productivity in a given year and the size of the population in the following year highlights the short generation time of 2-3 years and dependence of adult fidelity on nest success (Franken and Wellicome 2003; Todd et al. 2003). De Smet (1997) showed that successful territories in Manitoba were over three times more likely to be reoccupied the following year than failed territories, and successful territories when reoccupied in subsequent years were four times more likely to be successful in the subsequent years than reoccupied unsuccessful territories.

Long-term (6- to 15-year) banding and recapture datasets were used to estimate annual adult survival for Burrowing Owls in each of the three prairie provinces of Canada (Wellicome et al. 2014). Annual survival varied, among provinces and years, between 30 and 46% for adult males, and 16 and 38% for adult females. Annual survival of Canadian owls was reduced when storms occurred along the migratory route through the United States, and also when above-average precipitation occurred on the wintering grounds in Mexico, but was uninfluenced by indices of small mammal or grasshopper abundance on the breeding grounds over the same years (Wellicome et al. 2014).

Recruitment by juveniles is very low at 3.5% (in Manitoba; De Smet 1997) to 6% (in Regina Plain, Saskatchewan; Hoyt et al. 2001). These return rates are limited by the size of the respective study areas. Annual dispersal patterns are another consideration in this species’ life history. The species shows large average annual dispersal distances (Wellicome et al. 1997; Franken and Wellicome 2003; Duxbury 2004; Holroyd and Trefry 2011c; Holroyd et al. 2011). Duxbury (2004) found that return rates based on resighting of banded owls was positively correlated with study area size, indicating that dispersal of returning owls complicates calculation of true annual survival. He estimated a return rate in the Canadian prairies of ~50% based on stable isotope analysis of feathers of breeding owls, i.e., ~50% of breeding owls grew their feathers the previous year in Canada. The other ~50% of breeding owls grew their feathers in the US or Mexico the previous year. Overall the inter-annual dispersal distance of breeding owls was ~400 km. Based on the dispersal patterns of owls in the northern US states and Prairie Provinces, Duxbury (2004) estimated that the net emigration rate from Canada to the US less the reverse was 20% loss per year. The conclusion of his research is that factors affecting breeding populations in the US (and Mexico) could negatively affect Canadian populations.

In summary, Burrowing Owls have high potential reproductive potential but low productivity, low annual survival, and high rates of dispersal resulting in net emigration from Canada (Franken et al. 2003; Duxbury 2004; Environment Canada 2012; Wellicome et al. 2014).

The number of locations is large given the dispersed nature of the Burrowing Owl population and the various threats. Because many pairs of owls nest far from others, each nesting pair would be an effective location. Depending upon the surrounding habitats and land uses, the threats would differ with each situation. Consequently it is not practical to consider locations for Burrowing Owls.

In Canada, Burrowing Owl is nationally assessed as Endangered (COSEWIC 1995, 2000, 2006, and 2017) and listed as Endangered on Schedule 1 of SARA. The Recovery Strategy for the Burrowing Owl in Canada was completed in 2012 (Environment Canada 2012). Some of the recovery actions identified in the strategy have been initiated. Black-tailed Prairie Dog colonies in Canada are identified as critical habitat for Burrowing Owls (Government of Canada 2012). As most of these colonies are within Grasslands National Park, and described in the Canada Gazette, critical habitat destruction is prohibited under SARA.

Burrowing Owls are not covered under the federal Migratory Birds Convention Act, because raptors are excluded from it and are instead protected by the provincial wildlife acts in the four western provinces: B.C. Wildlife Act [RSBC 1996] CHAPTER 488; Alberta Wildlife Act, Office Consolidation, Revised Statutes of Alberta 2000, Chapter W-10; Saskatchewan Wildlife Act, 1998; and Manitoba Endangered Species and Ecosystems Act C.C.S.M. c. E111.

Provincially, the species is listed as Endangered in Manitoba (Manitoba 2015), Saskatchewan (Saskatchewan Environment 2015), and Alberta (Alberta Environment and Sustainable Resource Development 2014), and red-listed (equivalent to Endangered) in British Columbia (BC Conservation Data Centre 2017). Among states bordering Canada, it is also listed as Endangered in Minnesota (Minnesota Department of Natural Resources 2015), as a Species of Concern in Montana (Montana Natural Heritage Program 2015), and as a Candidate Species (for listing as Endangered, Threatened, or Sensitive) in Washington (Washington Department of Fish and Wildlife 2015).

For all Burrowing Owls on federal land (as defined in SARA), there are prohibitions under SARA against killing, harming, harassing, capturing, or taking individuals or their eggs, or damaging or destroying their burrows (see ‘residences’ in Environment Canada 2005). For Burrowing Owls within any of the four provinces of western Canada, provincial wildlife legislation has provisions that make it illegal to kill, injure, disturb, capture or possess a Burrowing Owl or its eggs, or to destroy a Burrowing Owl nest. Such provisions within federal or provincial legislation pertain to all Burrowing Owls or their nests, whether their locations are recorded by a government agency or are otherwise currently known or unknown.

NatureServe currently classifies Burrowing Owl as G4 (apparently secure globally because they occur in North and South America, although they may be quite rare in parts of their range), but this status has not been updated since 2004. Provincial NatureServe designations are S1B in Manitoba and British Columbia, and S2B in Saskatchewan and Alberta. S1B is defined as critically imperilled because of rarity, or a factor of species biology making it especially vulnerable to extinction. S2B refers to a species that is either very rare or local throughout its range, or found locally in a restricted range. The Canadian Endangered Species Conservation Council (CESCC) status ranking for Burrowing Owl is At Risk in all four western provinces (CESCC 2010). Summaries of the protection and legal status of Burrowing Owls in the United States and Canada can be found in Klute et al. (2003), McDonald et al. (2004), and NatureServe (2015).

The majority of suitable Burrowing Owl habitat in Canada is under private management. Habitat protection programs have therefore been initiated with voluntary land stewardship programs including Operation Burrowing Owl in Saskatchewan and Operation Grassland Community in Alberta. These programs encourage landowners to report the number of Burrowing Owls on their land each year, to protect nesting areas from cultivation and pesticide use, and to consider planting native grasses in place of cropland. Both programs have been successful in developing management plans for producers, raising the profile of native species, helping to retain native grasslands (Warnock and Skeel 2004), and also contributing valuable long-term data to Burrowing Owl monitoring efforts.

PRFA pastures contain some of the largest native grasslands remaining in Canada. The decision of the federal government to hand over 1.6 million acres of PFRA pastures in Alberta and Saskatchewan to the provincial governments has put the future management of these large tracts of native prairie in doubt (Herriot 2014).

All prairie dog colonies in Canada were identified as critical habitat in the Burrowing Owl Recovery Strategy (Environment Canada 2012). Most of these colonies are inside Grasslands National Park, and all Burrowing Owl critical habitat identified on federal protected areas land inside the Park has been gazetted (Government of Canada 2012). Beyond the critical habitat in prairie dog colonies, additional critical habitat has been identified in locations within southwestern Saskatchewan, where Burrowing Owls occupy Richardson's Ground Squirrel or American Badger burrows. This additional critical habitat was identified on November 20, 2017, when the Action Plan for Multiple Species at Risk in Southwestern Saskatchewan: South of the Divide (Environment and Climate Change Canada 2017) was posted on the SARA Registry (http://www.sararegistry.gc.ca/). Protection of Burrowing Owl habitat along migration routes (US) and on wintering grounds (Mexico) depends on whether these habitats happen to fall within conservation areas, which are not typically identified to target Burrowing Owl protection, in particular (Holroyd et al. 2001; Holroyd 2005).

This report was written with a heavy reliance on earlier COSEWIC reports: COSEWIC (2006), Wellicome and Haug (1995), Haug and Didiuk (1991), and Wedgwood (1978), as well as the Environment Canada (2012) recovery strategy. A number of regional experts have provided direct comments or published and unpublished information on the status and biology of Burrowing Owls in Canada in support of this status report:

Dawn Brodie, Researcher, Kamloops, BC.
Kaytlyn Burrows, Habitat Stewardship Coordinator, Operation Burrowing Owl, Nature Saskatchewan, Regina, SK.
Ken De Smet, Biologist, Wildlife & Ecosystem Protection Branch, Manitoba Conservation, Winnipeg, MB.
James Duncan, Director, Wildlife and Fisheries Branch, Manitoba Conservation and Water Stewardship, Winnipeg, MB.
Alex Froese, Project Manager, Manitoba Burrowing Owl Recovery Program, Winnipeg, MB.
Kerry Grisley, Manager, Operation Grassland Community, Alberta Fish and Game Association, Edmonton, AB.
Ray Poulin, Curator of Vertebrate Zoology, Royal Saskatchewan Museum, Regina, SK.
Helen Trefry, (retired) Canadian Wildlife Service, Environment Canada, Edmonton, AB.
Troy Wellicome, Wildlife Biologist, Canadian Wildlife Service, Environment Canada, Edmonton, AB.
Sharlyn Westworth, Wildlife Technician, Canadian Wildlife Service, Environment Canada, Edmonton, AB.

Funding was provided by the Canadian Wildlife Service, Environment Canada. The report writer thanks Marcel Gahbauer, COSEWIC Bird Sub-committee Co-Chair, for leading the production of this status report. The following people provided useful comments on earlier drafts: Peter Arcese, Louise Blight, Pam Sinclair, and Helen Trefry.

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Geoff Holroyd is a retired research scientist who worked for 36 years for the Canadian Wildlife Service, Environment Canada. His interest in birds developed as a teenager when he was an active volunteer with the Long Point Bird Observatory. He earned his MSc and PhD from the University of Toronto for his studies of the foraging strategies and diet of swallows. From 1976 to 1983, he supervised Ecological Wildlife Inventories of Banff, Jasper, Kootenay, Glacier and Mt Revelstoke National Parks. From 1983-1988 he was head of the Threatened Wildlife Section of the Canadian Wildlife Service. As a research scientist, he chaired the Peregrine Falcon Recovery Team from its start in 1987 to its end in 2012 and the Burrowing Owl Recovery Team for 8 years. He has studied wildlife in many parts of Canada and overseas including bats in South Africa, Blue Swallows in Malawi, Burrowing Owls in the US and Mexico, Little Owls in Spain, songbirds in Guatemala and owls in Ecuador. As an adjunct professor in the Department of Renewable Resources, University of Alberta, he co-supervised 14 graduate students. He was chair of the Prairie Conservation Action Plan subcommittee of World Wildlife Fund Canada. He organized the first Prairie Conservation and Endangered Species Workshop, served on the organizing committee of most of the subsequent conferences, and coedited the proceedings of the first three and the tenth conferences. He has published over 130 scientific and technical publications. He is currently chair of the Beaverhill Bird Observatory.

None, not applicable

Overall threat impact calculation help:
Threat impact Threat impact (descriptions) Level 1 Threat impact counts:
high range
Level 1 Threat impact counts:
low range
A Very high 0 0
B High 1 1
C Medium 4 2
D Low 1 3
- Calculated overall threat impact: Very High Very High
Threat table
Threat Threat description Impact (calculated) Impact description (calculated) Scope (next 10 Yrs) Severity (10 Yrs or 3 Gen.) Timing Comments
1 Residential & commercial development blank cell Negligible Negligible (<1%) Extreme - Serious (31-100%) High - Moderate blank cell
1.1 Housing & urban areas blank cell Negligible Negligible (<1%) Extreme - Serious (31-100%) High - Moderate Very few owls are likely to be displaced by expansion of housing over the next ten years. Some urban areas have already been abandoned (e.g., Moose Jaw); many urban areas currently not expanding either. Medicine Hat may be an exception to this, with some growth into surrounding areas with suitable habitat for Burrowing Owls. However, even where urban development occurs, displacement is not necessarily complete; range of extreme-serious best captures range of possibilities.
1.2 Commercial & industrial areas blank cell Negligible Negligible (<1%) Extreme - Serious (31-100%) High - Moderate Expansion of commercial and industrial areas likely to affect even fewer owls than housing and urban areas, but severity would be comparable.
1.3 Tourism & recreation areas blank cell Negligible Negligible (<1%) Serious - Moderate (11-70%) High - Moderate Some development ongoing in Grasslands National Park, including trail expansion and campgrounds in the East Block; elsewhere in range, development of tourism and recreation areas likely to be limited. Most activities underway or proposed would only have a moderate effect on owls, but those with a larger footprint could be serious.
2 Agriculture & aquaculture D Low Restricted - Small (1-30%) Moderate - Slight (1-30%) High (Continuing) blank cell
2.1 Annual & perennial non-timber crops D Low Restricted - Small (1-30%) Moderate - Slight (1-30%) High (Continuing) A minority of owls are likely to be exposed to new land conversion or intensification of agriculture. Historically, conversion of land to agriculture is believed to have been among the factors in the decline of Burrowing Owls. However, extent of agriculture has largely stabilized in Canada, although there is still some expansion on the wintering range, especially in Mexico (e.g., lettuce, agave). Severity varies by ecological context and scale. Some studies have shown an increase in Burrowing Owls where agriculture and irrigation expand (e.g., Salton Sea area), largely believed to be a function of converting relatively barren landscapes into more productive ones. Some Burrowing Owls in Canada are also known to nest successfully in hay and other crops. Scobie (2015) found no negative effect of crops on Burrowing Owls in a review of 850 nesting attempts over 2 years in Alberta and Saskatchewan. While the effect may be neutral or even positive in some cases, the historical context and potential for direct negative effects of agricultural practices combine to result in an overall moderate-slight severity.
2.2 Wood & pulp plantations blank cell blank cell blank cell blank cell blank cell blank cell
2.3 Livestock farming & ranching blank cell Not a Threat Pervasive (71-100%) Neutral or Potential Benefit High (Continuing) Most Burrowing Owls will be exposed to ranching at some point in their life cycle. Typically the species fares well where there is grazing, and has disappeared from areas where grazing was stopped; the severity is therefore neutral or potentially beneficial.
2.4 Marine & freshwater aquaculture blank cell blank cell blank cell blank cell blank cell blank cell
3 Energy production & mining CD Medium - Low Restricted (11-30%) Serious - Moderate (11-70%) High (Continuing) blank cell
3.1 Oil & gas drilling blank cell Negligible Small (1-10%) Negligible (<1%) High (Continuing) Relatively few Burrowing Owls are likely to be affected by oil and gas drilling, though this in part may be a function of previous displacement; current downturn in oil/gas economy also limits expansion plans in the near future. Mitigation measures (e.g., timing restrictions, setbacks) are enforced to reduce any effects at such facilities, therefore severity is likely to be negligible. No published studies have demonstrated an effect on Burrowing Owls.
3.2 Mining & quarrying blank cell Negligible Negligible (<1%) Negligible (<1%) High (Continuing) Potash and gravel mining occurring in Alberta and Saskatchewan, but likely to affect very few Burrowing Owls. Mitigation measures would be required for any such developments. While habitat loss would result, footprint is generally small enough that owls can move to other locations nearby; therefore severity is negligible.
3.3 Renewable energy CD Medium - Low Restricted (11-30%) Serious - Moderate (11-70%) High (Continuing) Big push in Alberta for expansion of wind and solar energy production, with 2000-3000 turbines expected to be built over the next 10-15 years; 75% of applications to date are within Burrowing Owl range, though not necessarily near owls. Potential effects include habitat fragmentation and loss (especially with large solar installations) and direct mortality (primarily from wind turbines). Data from Altamont wind farms in California indicate that Burrowing Owl is among the leading victims of turbine collisions (see Smallwood et al. 2007). Solar and wind developments are also underway throughout much of wintering and migration range.
4 Transportation & service corridors C Medium Pervasive (71-100%) Moderate (11-30%) High (Continuing) blank cell
4.1 Roads & railroads C Medium Pervasive (71-100%) Moderate (11-30%) High (Continuing) Almost all Burrowing Owls expected to be exposed to roads. The species is known to be vulnerable to vehicle collisions, with two studies suggesting mortality rates of 15% and 31%.
4.2 Utility & service lines blank cell blank cell blank cell blank cell blank cell Direct effects unlikely; increase in predation related to expansion of such lines is treated under section 8.2
4.3 Shipping lanes blank cell blank cell blank cell blank cell blank cell blank cell
4.4 Flight paths blank cell blank cell blank cell blank cell blank cell blank cell
5 Biological resource use blank cell blank cell blank cell blank cell blank cell blank cell
5.1 Hunting & collecting terrestrial animals blank cell blank cell blank cell blank cell blank cell While Burrowing Owls have potentially been shot on occasion, it is not believed that this is an ongoing threat. Effects of unintentional poisoning (e.g., through pest control) are addressed under 7.3.
5.2 Gathering terrestrial plants blank cell blank cell blank cell blank cell blank cell blank cell
5.3 Logging & wood harvesting blank cell blank cell blank cell blank cell blank cell blank cell
5.4 Fishing & harvesting aquatic resources blank cell blank cell blank cell blank cell blank cell blank cell
6 Human intrusions & disturbance blank cell Negligible Restricted (11-30%) Negligible (<1%) High (Continuing) blank cell
6.1 Recreational activities blank cell Negligible Small (1-10%) Negligible (<1%) High (Continuing) A small part of the population (particularly in parks or other protected areas) may be exposed to disturbance by the public, including photographers. While this may cause temporary disturbance, there is no evidence that severity is more than negligible.
6.2 War, civil unrest & military exercises blank cell Negligible Small (1-10%) Negligible (<1%) High (Continuing) The Suffield National Wildlife Area supports around 8 pairs of Burrowing Owls (~3% of known population); potential for occasional mortality or destruction of burrows as a result of military activity, but likely rare and of negligible severity overall.
6.3 Work & other activities blank cell Negligible Restricted (11-30%) Negligible (<1%) High (Continuing) Grasslands National Park has around 17 pairs of Burrowing Owls (~7% of known population); both the owls and other species in their habitat (e.g., Black-tailed Prairie Dogs) are subjects of research, but care is exercised to limit disturbance, and severity is expected to be negligible. Burrowing Owls are also monitored (including banding) at various locations outside the park, with similarly limited effects.
7 Natural system modifications B High Pervasive (71-100%) Serious (31-70%) High (Continuing) blank cell
7.1 Fire & fire suppression blank cell Unknown Large (31-70%) Unknown High (Continuing) The natural fire cycle in the prairies is approximately 25 years, but with fire suppression has increased to as much as 250 years; vegetation build up may be detrimental to Burrowing Owls (e.g., foraging more efficient in areas with low litter). Prescribed burns in some areas (e.g., Grasslands National Park) are likely beneficial. Fire occurring while nesting could have negative effects, but at other times is likely positive; overall severity is unknown.
7.2 Dams & water management/use blank cell blank cell blank cell blank cell blank cell blank cell
7.3 Other ecosystem modifications B High Pervasive (71-100%) Serious (31-70%) High (Continuing) Most Burrowing Owls are exposed to areas where rodenticides and insecticides affect prey availability and condition. Loss of prey base can have a considerable impact on the owls; if fossorial species that provide suitable burrows are affected as well, this can influence habitat suitability for owls even more. Undergrazing (i.e., vegetation too tall for effective hunting) can also make otherwise potentially suitable habitat unattractive. Effects of invasive plants on Burrowing Owls are not well documented, but may also be a concern if they reduce bare ground cover. Native predators are addressed under 8.2.
8 Invasive & other problematic species & genes CD Medium - Low Pervasive (71-100%) Moderate - Slight (1-30%) High (Continuing) blank cell
8.1 Invasive non-native/alien species blank cell Negligible Small (1-10%) Negligible (<1%) High (Continuing) Primarily feral cats; potentially also some effect by domestic dogs, and by Raccoons which have expanded into the Prairies. Mortality most likely to affect nestlings or young fledglings, and therefore little direct effect on the population.
8.2 Problematic native species CD Medium - Low Pervasive (71-100%) Moderate - Slight (1-30%) High (Continuing) Burrowing Owls may be experiencing greater predation pressure from larger raptors due to general increase in the population of those species. The situation may be exacerbated in areas where new perches / nest sites become available through development of facilities (e.g., utility lines and poles). Abandonment of human dwellings and barns also provides nesting sites for Great Horned Owls and other native predators. Almost all Burrowing Owls are likely to be exposed to increases in predator numbers, but the degree of severity is not well documented; likely in the moderate-slight range.
8.3 Introduced genetic material blank cell blank cell blank cell blank cell blank cell blank cell
9 Pollution blank cell Negligible Small (1-10%) Negligible (<1%) High (Continuing) blank cell
9.1 Household sewage & urban waste water blank cell blank cell blank cell blank cell blank cell blank cell
9.2 Industrial & military effluents blank cell blank cell blank cell blank cell blank cell blank cell
9.3 Agricultural & forestry effluents blank cell Negligible Small (1-10%) Negligible (<1%) High (Continuing) There is potential for strychnine to kill juvenile and adult owls, although research has shown this to be unlikely when used at recommended concentrations. DDE is also a threat that affects prey species. It can have a particularly negative impact on malnourished fledglings because they will tend to metabolize fat & protein stores where this chemical is stored.
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9.5 Air-borne pollutants blank cell blank cell blank cell blank cell blank cell blank cell
9.6 Excess energy blank cell blank cell blank cell blank cell blank cell blank cell
10 Geological events blank cell blank cell blank cell blank cell blank cell blank cell
10.1 Volcanoes blank cell blank cell blank cell blank cell blank cell blank cell
10.2 Earthquakes/tsunamis blank cell blank cell blank cell blank cell blank cell blank cell
10.3 Avalanches/landslides blank cell blank cell blank cell blank cell blank cell blank cell
11 Climate change & severe weather C Medium Large (31-70%) Moderate (11-30%) High (Continuing) blank cell
11.1 Habitat shifting & alteration blank cell blank cell blank cell blank cell blank cell blank cell
11.2 Droughts blank cell Unknown Restricted (11-30%) Unknown Moderate (Possibly in the short term, < 10 yrs) Droughts appear to be beneficial to owls in Canada, likely due to high prey availability (ground squirrels and grasshoppers). However, elsewhere drought has been associated with declines in reproductive success, and effects of drought on wintering grounds are not well documented. Some part of the population is likely to be affected, but severity is unknown
11.3 Temperature extremes blank cell blank cell blank cell blank cell blank cell blank cell
11.4 Storms & flooding C Medium Large (31-70%) Moderate (11-30%) High (Continuing) Storm severity could increase with climate change. A large part of the population is likely to be affected by storms at some point in their life cycle (40 mm of rain is a threshold for flooding, but starvation may occur already with 20-40 mm of rain). The effect is greatest on nestlings, but there may be a moderate effect on adults too.

Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).

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