COSEWIC Assessment and Status Report on the Savannah Sparrow Passerculus sandwichensis princeps subspecies in Canada – 2009

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Document Information

List of Figures


Document Information

Savannah Sparrow Passerculus sandwichensis princeps subspecies

Photo of a Savannah Sparrow Passerculus sandwichensis.

Special Concern – 2009

COSEWIC -- Committee on the Status of Endangered Wildlife in 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. 2009. COSEWIC assessment and status report on the Savannah Sparrow princeps subspecies Passerculus sandwichensis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 21 pp.

Previous report(s):

COSEWIC. 2000. COSEWIC assessment and update status report on the Savannah Sparrow princeps subspecies Passerculus sandwichensis princeps in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 13 pp.

Horn, A.G. 2000. Update COSEWIC status report on the Savannah Sparrow princeps subspecies Passerculus sandwichensis princeps in Canada, in COSEWIC assessment and update status report on the Savannah Sparrow princeps subspecies Passerculus sandwichensis princeps in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 1–13 pp.

McLaren, I.A. 1979. COSEWIC status report on the Ipswich Sparrow Passerculus sandwichensis princeps in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 14 pp.

Production note:
COSEWIC would like to acknowledge Andrew G. Hornfor writing the status report on the “Ipswich”subspecies of the Savannah Sparrow princeps subspecies Passerculus sandwichensis princeps in Canada, prepared under contract with Environment Canada, overseen and edited by Jon McCracken, Co–chair, COSEWIC Birds Species Specialist Subcommittee.

For additional copies contact:

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

Tel.: 819–953–3215
Fax: 819–994–3684
E–mail
Website

Également disponible en français sous le titre Évaluation et Rapport de situation du COSEPAC sur le Bruant des prés de la sous–espèce princeps (Passerculus sandwichensis) au Canada.

Cover illustration/photo:
Savannah Sparrow -- Photo courtesy Ian A. McLaren.

© Her Majesty the Queen in Right of Canada, 2010.
Catalogue CW69–14/275–2010E–PDF
ISBN 978-1-100-15055-0

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COSEWIC Assessment Summary

Assessment Summary – November 2009

Common name
Savannah Sparrow

Scientific name
Passerculus sandwichensis princeps subspecies

Status
Special Concern

Reason for designation
This songbird is largely restricted to the sandy dune systems of Sable Island, NS. The population has increased over recent decades and now shows signs of stability because the island has reached carrying capacity. The bird is not prone to human disturbance because the breeding location is well protected. The subspecies is also multi–brooded and currently experiences good nesting success, which confers good reproductive potential to cope with potential catastrophic events. Nevertheless, its breeding range is restricted to a very small area of Canada, and it has a relatively small population. It is also exposed to ongoing threats associated with development of its shoreline wintering habitat in the eastern U.S., and is vulnerable to sea–level rise and increasing frequency and intensity of Atlantic storms that are projected to occur as a result of climate change.

Occurrence
Nova Scotia

Status history
Designated Special Concern in April 1979. Status re–examined and confirmed in May 2000 and in November 2009.

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COSEWIC Executive Summary

Savannah Sparrow Passerculus sandwichensis princeps subspecies

Species Information

Passerculus sandwichensis princeps is a subspecies of the Savannah Sparrow that is commonly known as “Ipswich sparrow.” It is distinguished from the other subspecies of Savannah Sparrow mainly by its larger size and greyer, paler plumage. A recent genetic study of variation in mitochondrial DNA shows no strong genetic difference between Ipswich sparrows and other Savannah Sparrows. Nevertheless, a recent morphological study suggests that the subspecific status should be retained.

Distribution

Ipswich sparrows do not breed outside Canada. They nest almost exclusively on Sable Island, Nova Scotia. A few individuals, perhaps fewer than 10 per year, interbreed with the more common subspecies of Savannah Sparrow on the adjacent mainland. The birds winter in coastal areas from southern Nova Scotia to northern Florida.

Habitat

The birds breed on virtually all vegetated areas on Sable Island, including heathy terrain and areas dominated by Marram Grass. In winter, they occur in coastal dunes, especially in areas with dense beach grass. The availability of breeding habitat on Sable Island appears to have been stable over time. In contrast, much wintering habitat may have been lost historically, although the trend has slowed in recent years. Sable Island is protected as a Migratory Bird Sanctuary, and much of the wintering range is either protected or under regulations that prevent degradation of dune habitat. The degree of protection of wintering habitat is hard to evaluate, however, without more detailed information on the bird’s microhabitat needs.

Biology

The ecology and demographics of the Ipswich sparrow have been well studied. Males are polygynous, and each season a pair can raise up to three broods of about five young each. Predation rates are low because Sable Island has no terrestrial predators. Thus, reproductive rate, and in turn the ability of the population to recover from temporary declines, is high. Overwinter survival appears to be the most important limiting factor.

Population sizes and trends

Censuses during the breeding season and Christmas Bird Count data from the wintering range both suggest that the population size has doubled over the past two decades, and remained relatively stable over the past decade. The current population is estimated to be about 6000 mature individuals.

Limiting factors and threats

The restriction of the entire breeding population to one small island makes it vulnerable to local and chance events. The most important threats to the population are destruction and degradation of wintering habitat and harsh weather during the migration or wintering periods. The island is particularly vulnerable to sea–level rise and increases in the frequency and intensity of Atlantic storms that are projected to occur as a result of climate change.

Special Significance of the Species

The Ipswich sparrow is perhaps Canada’s best known “endemic” breeding songbird, well known and valued by naturalists, especially in the eastern US. Also, since its discovery, it has been at the centre of an ongoing controversy over how bird taxa should be defined at the species level.

Existing protection

Ipswich sparrows are protected by Canada’s Migratory Birds Convention Act, 1994 and the United States’ Migratory Bird Treaty Act, 1918. COSEWIC assessed this species as Special Concern in May 2000, and it is currently listed as Special Concern in Schedule 1 of the Species at Risk Act. Sable Island is a Migratory Bird Sanctuary, which further protects the birds and their nests, and may soon be designated as a National Wildlife Area, which may increase regulation of activities on the island.

COSEWIC History

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.

COSEWIC Mandate

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 Membership

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.

Definitions (2009)

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)
A wildlife species that no longer exists.

Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A wildlife species facing imminent extirpation or extinction.

Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)**
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)***
A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

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

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COSEWIC Status Report on the Savannah Sparrow Passerculus sandwichensis princeps subspecies in Canada – 2009

Species Information

Name and classification

The “Ipswich” subspecies of the Savannah Sparrow (Passerculus sandwichensis princeps), or Ipswich sparrow, as it is more usually known (informally, and thus uncapitalized), is a locally distributed subspecies of the Savannah Sparrow, a species found throughout North America. It is a member of the subfamily Emberizinae, a taxon that includes New World sparrows and Old World buntings and is part of the largest family in the Order Passeriformes, the Emberizidae. The Savannah Sparrow includes several other geographical and morphological variants whose subspecific and even species status is disputed. Until 1973, the American Ornithologists’ Union (AOU) considered the Ipswich sparrow to be a distinct species, based on its morphology, plumage, and restricted, isolated breeding range. In 1973, the AOU relegated the race to subspecies status, because of reports of interbreeding with “typical” Savannah Sparrows on the mainland of Nova Scotia (Stobo and McLaren 1975). Recent genetic work (see below) supports this taxonomic status, although whether the population should be considered a subspecies or a full species is still uncertain.

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Morphological description

Ipswich sparrows are superficially similar to other types of sparrow, such as the much more familiar and widespread races of the Savannah Sparrow or the Song Sparrow, Melospiza melodia. Like them, they are small songbirds with conical beaks, and are dull coloured overall with streaked breasts. Ipswich sparrows are similar to other Savannah Sparrows, with a distinctive yellow area between their eye and beak and a notched tail, but they are much paler and greyer overall, with narrower breast stripes that have a pinkish cast. Ipswich sparrows are also larger and heavier set than almost all other races of Savannah Sparrow (Rising 2001) and usually walk rather than hop while foraging (Hailman 1958). Their song is similar to that of other Savannah Sparrows in their range, but perhaps slightly lower–pitched (Horn unpub. data). It varies among individuals, but is invariably a two–second long series of thin short notes followed by a trill and then a flourish, one possible rendering being “tsip tsip tsiptsip pcheeeeeeweecheuw.”

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Genetic description

Savannah Sparrows vary in morphology and plumage across their range, such that 28 subspecies have been named (Wheelwright and Rising 2008). Most of this variation is clinal, however (Rising 2007), so Wheelwright and Rising (2008) list only 17 distinguishable subspecies, including the Ipswich sparrow. Ipswich sparrows rarely but perhaps regularly interbreed with Savannah Sparrows on or from the adjacent mainland in Nova Scotia, where the predominant subspecies is P. s. savanna. The frequency of interbreeding has been measured twice. First, in the only census to search all of Sable Island from end to end, in summer 1971, seven "typical" (i.e., mainland) Savannah Sparrows (some of which were dark enough to possibly be of the subspecies P. s. labradorius) were found among 2424 Ipswich sparrows. Second, on the Nova Scotia mainland west of Sable Island, in the same summer, an intensive search of 13 km of coastal habitat revealed two mixed pairs, only one of which raised flying young (Stobo and McLaren 1975). Further evidence of the rarity of interbreeding comes from the Maritime Breeding Bird Atlas (Erskine 1992; MBBA 2008). During the first atlas project (1986–1990) only one bird was found breeding on the mainland (feeding young in Guysborough County; S. Blaney, pers. comm. 2008). To date, the second atlas project (2006–2008) has yielded only one record with evidence of possible breeding (a bird found in suitable breeding habitat during the breeding season in Halifax County; MBBA 2008).

Stobo and McLaren (1975) suggest that gene flow from Sable Island to the mainland might be greater than gene flow in the reverse direction, because Ipswich sparrows have a longer breeding season than mainland birds and because hybrid offspring would be less likely to return to Sable Island than to the mainland. Interestingly, all five Ipswich sparrows that have been found on the mainland during the breeding season were female (based on lack of singing and other territorial behaviours), which weakly suggests a reproductive isolating mechanism related to mate choice (Stobo and McLaren 1975) or perhaps sex differences in dispersal patterns.

In the only genetic study of differentiation between Ipswich sparrows and other Savannah Sparrows, Ipswich sparrows were not reciprocally monophyletic from “typical” Savannah Sparrows collected from sites scattered widely across North America, from Newfoundland to Alaska (Zink et al. 2005). Indeed, Savannah Sparrows as a whole fell into two main groups (mitochondrial DNA haplotypes) that co–occurred throughout North America; the only exceptions were birds from two morphologically distinct populations in California and Mexico, at least one of which may be a distinct species (Figure 1). Thus, while the genetic results suggested that there is little gene flow into Sable Island’s “Ipswich” population and that this population is of relatively recent origin, the study did not provide evidence for distinguishing Ipswich sparrow as a distinct species (Zink et al. 2005).

Nonetheless, the methods used (analysis of the mtDNA control region) were based on a small portion of the genome and are an indirect and perhaps weak test of reproductive isolation (Remsen 2005), especially considering the distinctiveness of Ipswich sparrows in other respects (Zink 2006). Indeed, a recent analysis of the bird’s distinctive morphological features in the context of variation within Savannah Sparrows across North America has already supported its taxonomic status as at least a subspecies (Rising 2007; Wheelwright and Rising 2008).

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Designatable units

The information reviewed above shows that the Ipswich sparrow represents a single designatable unit for several reasons: 1) it has been consistently acknowledged to be distinct from other Savannah Sparrows, either at the subspecies or species level; 2) its breeding range is geographically disjunct from that of other subspecies; 3) its gene flow with other subspecies is extremely limited, and 4) it shows distinctive features, such as lighter plumage, that may be an evolutionary result of its restriction to sandy beach and dune habitats.

Figure 1. Neighbour–joining tree of pair–wise distances of Savannah Sparrow haplotypes sampled from across North America, with percentage of bootstrap replicates supporting nodes given if > 60%. Sable Island (Ipswich sparrow) haplotypes are labeled “SAB” (from Zink et al. 2005; further details therein).

Neighbour-joining tree diagram of pair-wise distances of Savannah Sparrow haplotypes sampled from across North America, with percentage of bootstrap replicates supporting nodes given if greater than 60 percent.

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Distribution

Global range

The breeding range of Ipswich sparrows is almost exclusively restricted to Sable Island, Nova Scotia. The birds winter in coastal dune habitats, particularly those with direct seaward exposure, from southern Nova Scotia to northern Florida (Figure 2). In the 1970s, a census across the wintering range and an analysis of Christmas Bird Count (CBC) data showed the highest concentration of birds to lie between New Jersey and Virginia (Stobo and McLaren 1971). Since then, an analysis of CBC data suggests that the centre of abundance of wintering birds appears to have shifted about 160 km south, but changes in neither the northern limit, southern limit, nor centre of occurrence were statistically significant (Dale 2007).

Vagrant individuals have occurred at various locations, mainly slightly inland of the North American Atlantic coast, with exceptional sightings near Port Stanley in southern Ontario, Quebec City in Quebec, and Portland Bill in Devon, United Kingdom (McLaren and Horn 2006).

Figure 2. Summer breeding range (Sable Island) and wintering range (greyed coastline) of the Ipswich sparrow (after Stobo and McLaren 1971; Horn 1999; Dale 2007).

Map showing summer breeding range and wintering range of the Ipswich sparrow.

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Canadian range

Although virtually all individuals breed on Sable Island, as noted above, in at least some years some individuals breed along the Nova Scotia mainland coast.

The area of occupancy is the vegetated area of Sable Island (except areas of sandwort), which is 10 km² (Stobo and McLaren 1975). Using the International Union for Conservation of Nature (IUCN) standard grid size of 2X2 km to overlay this vegetated area yields an index of area of occupancy of 80 km². The bird’s extent of occurrence in Canada, the minimum convex polygon enclosing this area, is 90 km².

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Habitat

Habitat requirements

Ipswich sparrows breed in nearly all vegetated areas on Sable Island, particularly heathy areas dominated by shrubs, which are characteristic of stable terrain on the island, as well as areas where Marram Grass (Ammophila breviligulata) is particularly dense. The only areas they clearly avoid are those dominated by Sandwort (Honckenya peploides; Stobo and McLaren 1975). Heathy terrain is settled first (and thus presumably preferred), has higher densities of birds, and yields higher breeding success than marram–dominated habitat (Stobo and McLaren 1975; Ross 1980a). The suggestion in the previous status report that breeding habitat was a limiting factor (Horn 1999) was clearly premature. It was based largely on low reproductive output in 1995, a year that had more censused birds than in any previous year (Temple 1996). Since then, however, the breeding population appears to have nearly doubled in size, so, in retrospect, habitat was not limiting.

During winter, Ipswich sparrows are found strictly on coastal beaches and dunes, particularly their seaward portions. The only study of winter habitat use, a census conducted throughout the wintering range, found more individuals in locations with extensive areas of thick beach grass, a weak association with access to freshwater, and no significant correlation with topographical relief (McLaren and Horn 2006, re–analyzing results of Stobo and McLaren 1971). Otherwise habitat use in winter has not been studied.

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Habitat trends

Despite some reports that Sable Island’s vegetation is eroding or being destroyed by the island’s resident population of horses, there is no evidence that the amount of vegetated habitat or its composition has changed appreciably over the past century (Gray 1992; McCann and Byrne 1994; Byrne and McCann 1995; Freedman 1996; Stalter and Lamont 2006).

The habitat needs of Ipswich sparrows in winter are poorly understood. Thus, trends in wintering habitat can only be inferred from more general data on overall trends in dune beach habitat, much of which has been destroyed historically by dense human settlement along the eastern seaboard of the US. For example, by 1975, 21% of barrier islands in the mid–Atlantic states had been developed (Watts 1999). Even as recently as between 1970 and 1990, the human population in the coastal zone increased 5–90% among states in the wintering range of Ipswich sparrows, with only one state reporting declines (New York; 5%) and states in the centre of the birds’ range (Maryland, Virginia, and North Carolina) reporting increases of 12%, 40%, and 39% (Bernd–Cohen and Gordon 1998). In these three states, 9%, 26%, and 15% of shoreline was determined to be “critically eroding” in 1970 (Bernd–Cohen and Gordon 1998).

The ecological value of beach and dune habitat is now being recognized and management of them has thus improved, but inventories are too incomplete to estimate habitat trends (Davis 2003). Also, how these new management efforts affect the particular habitat needs of Ipswich sparrows is unclear. In particular, the limited data available on those needs suggest that the bird might prefer habitats that are less pristine than those that are the targets of most conservation efforts (Stobo and McLaren 1971).

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Habitat protection/ownership

Sable Island, where virtually all individuals breed, is a Migratory Bird Sanctuary, so the birds and their nests are protected by the Migratory Bird Sanctuary Regulations of the Migratory Birds Convention Act. Access to the island and activities on it have been regulated by the Canadian Coast Guard through the Canada Shipping Act. Management of the island is now the responsibility of Environment Canada, which drafted a conservation strategy for the island in 1998 (Beson 1998). Designation of the island as a National Wildlife Area is pending; this will offer no additional protection per se but will require development of a management plan that specifies which activities are allowed, which require a permit, and which are prohibited. The island is also a globally Important Bird Area, which again does not offer additional protection, but does formally recognize the island’s significance, in part because it holds the entire breeding range of the sparrow.

Protection of wintering habitat varies through the wintering range, but not all wintering sites have been identified, so the quality and extent of protection can only be roughly estimated. Over 90% of coastal beach and dune habitats along the US east coast are privately owned. Some of these lands are private refuges, and the others are under various provincial, state, and municipal regulations directed at preventing dune destruction and erosion (Bernd–Cohen and Gordon 1998). Most publicly owned sites are State Parks, National Wildlife Refuges, National Parks, and National Seashores, all of which offer strong protection of habitats in their natural state (Bernd–Cohen and Gordon 1998). Most Ipswich sparrows found in the winter survey by Stobo and McLaren (1971) and reported in Christmas Bird Counts are on public lands, but these areas are also the ones most likely to be surveyed.

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Biology

Intensive studies in the late 1960s and 1970s (Stobo and McLaren 1975; Ross 1979, 1980a,b, 1981) yielded a thorough understanding of the bird’s biology, especially its ecology and demographics. Since then, several studies focused on particular topics have appeared, including several published since the previous status report (Horn 1999) was written.

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Life cycle and reproduction

Ipswich sparrows arrive on Sable Island in mid– to late April, and males start defending their 1– to 2–hectare territories soon thereafter. About 25% of males are bigamous (< 5% are trigamous; Stobo and McLaren 1975), which might slightly reduce the effective population size, relative to a monogamous population. Females lay clutches of three to five eggs in a concealed nest on the ground. Incubation, by the female, lasts about 13 days, and young are fed by both parents. Young leave the nest about 11 days after hatching, and are fed, especially by the male, for two to three weeks thereafter. Females can start another nest and lay within days after young have left the previous nest. Thus, first egg dates generally range from mid–May to mid–August (Stobo and McLaren 1975).

Ipswich sparrows appear to have high survival and fecundity. They breed in their first year, adult return rates are 28–42%, fledging success appears to be very high in most years (72–84% in Stobo and McLaren 1975), and females can successfully produce two broods per year (90% of females in Stobo and McLaren 1975), with many producing up to three (40% of females in Stobo and McLaren 1975). As with other island populations without introduced predators, predation rates are low for a ground nesting passerine, varying from 0% to 20% (Ross 1979, 1980a; Horn 1999; C. Dale pers. comm. 2008).

Overwinter survival appears to be the most important limiting factor on the population. Some evidence for this comes from unusually low CBC totals from 1976 to 1979, which were preceded by three harsh winters and low overwinter survival (McLaren 1979; Ross and McLaren 1981). More generally, overwinter survival, measured as the population size in spring relative to its size late in the previous summer, decreases significantly across years as precipitation in the winter range increases, again suggesting that fewer birds return after harsher winters (McLaren and Horn 2006). Moreover, this pattern across years is significantly stronger the more birds there are at the start of the winter, suggesting that winter survival is density dependent (McLaren and Horn 2006).

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Herbivory/predation

Ipswich sparrows eat a wide range of seeds and insects, primarily the seeds of Marram Grass in the summer and Sea Oats (Uniola paniculata) in the winter (Stobo and McLaren 1971, 1975). As far as is known, nestlings and fledglings are fed only insects.

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Physiology

No physiological studies have been conducted.

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Dispersal/migration

Birds leave wintering grounds in mid–March and most arrive in Nova Scotia in the first two weeks of April, when they concentrate along mainland shores west of Sable Island, departing for the island on days with good weather and tailwinds (Stobo and McLaren 1975). They begin leaving Sable Island again by late September or early October, with most birds passing through Nova Scotia in mid–October, reaching the southern half of the wintering range sometime in November (Stobo and McLaren 1975).

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Interspecific interactions

Potential predators on Sable Island are all birds, and include gulls (mainly Herring Gull, Larus argentatus and Great Black–backed Gull, L. marinus), American Crows (Corvus brachyrhynchos), Common Grackles (Quiscalis quiscala), and several species of migrant and vagrant raptors (Ross 1979). Ross (1979) also lists European Starlings (Sturnus vulgaris) and Red–winged Blackbirds (Agelaius phoeniceus) as potential predators, although this seems unlikely. Indeed the only identified predator was a Great Black–backed Gull that depredated one nest (Horn 1999). Ross (1980b) also reported, but did not quantify, a few cases in which nests were trodden on by horses. Raptors are presumably the main predators during migration and in winter (Stobo and McLaren 1975).

About 200–350 horses roam freely on Sable Island, undoubtedly affecting sparrow habitat. Exclosure experiments suggested they may affect the composition but do not reduce the extent of vegetation on the island (Welsh 1976). Specifically, on the consolidated heathland habitats, they arrest succession to woody shrubs (Welsh 1976), which are avoided by Savannah Sparrows elsewhere (Potter 1974; Weatherhead 1979).

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Adaptability

Ipswich sparrows are strictly associated with coastal dune habitat. Their small area of occupancy during the breeding season leaves them vulnerable to chance events, although their high reproductive rate helps the population recover quickly from short–term declines. The birds appear to be very tolerant of human activities near their nesting areas (Stobo and McLaren 1975).

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Population Sizes and Trends

Search effort

The breeding population was first formally censused in annual counts between 1967 and 1979, and again in 1995 (McLaren 1979; Horn 1999). Up to 16 areas averaging 3 ha in size and roughly rectangular in shape were censused by at least three counters walking in parallel. The areas were selected to have roughly uniform habitat while collectively representing the proportions of habitat types on the island as a whole. The number of birds flushed in each habitat type was then multiplied by the proportion of each habitat known (from aerial photos) to be on the island (Stobo and McLaren 1975).

In 1998, the population was censused by walking across the island along four to five transects placed at random intervals within each of seven bands that evenly divided the island and thus stratified the transects based on habitat and topography. Randomization allowed calculation of confidence intervals for the population estimate, which previous censuses did not. A stratified random, rather than random, selection of transects was used because the island’s habitats change across its length, roughly from sparse marram to dense marram to heath as one moves towards the island’s centre (Smith et al. 2003).

In 2006, both the pre–1998 and the 1998 census methods were used, with slight modifications, so that the two census methods could be calibrated to each other (Horn 2007).

The wintering population is surveyed yearly by the Christmas Bird Count (CBC), in which all bird species within 24–km radius “count circles” spaced throughout much of North America are counted by volunteers. Each count circle is surveyed on a single day between December 14 and January 5. For many species, CBCs provide good information on winter distributions and population trends, but for Ipswich sparrows data are sparse. Counting Ipswich sparrows requires walking through dune habitat near outer beaches, so totals probably vary strongly with the shifting motivation of counters, especially under varying weather conditions, and may bear little relationship to search effort expended in other areas of a count circle. For example, a sharp drop in count totals followed the change in the bird’s status from species to subspecies in the 1970s (McLaren 1979; Figure 3). Short of interviewing count participants, arguably the only measure of whether the bird was searched for is whether it was detected at all (Stobo and McLaren 1975; McLaren 1979). Thus in the analyses below, search effort is taken into account by dividing the total number of birds by the number of count circles in which Ipswich sparrows were reported for each year (dividing by the number of participants in those counts yielded similar results, but in less readily interpretable units). Clearly, this is only one possible approach for dealing with these sparse and likely biased data, so its results should be used cautiously.

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Abundance

Regular censuses in early June between 1967 and 1979 showed 2100 to 3300 individuals on the island, except for 1977 and 1978, when 1700 and 1250 individuals, respectively, were estimated. By 1979 the estimate had risen to nearly 2000 individuals (Ross and McLaren 1981). The next census, in 1995, yielded 3400 individuals (Horn 1999).

In 1998, a new census method estimated 5962 ±546.8 individuals (Smith et al. 2003). In 2006, the new method and previous method were used in parallel by one field team. The results were similar – 6789 and 6671 individuals for the old and new methods, respectively – suggesting that the change in numbers between 1967–1979 and 1998–2006 reflected an increase in the population rather than a change in sampling methods (Horn 2007).

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Fluctuations and trends

As noted above, the summer population dipped to 1700 and 1250 individuals in 1977 and 1978, respectively, having held steady between 1967 and 1979 at 2100–3300 individuals. The fluctuation is thought to have been caused by particularly harsh winters (McLaren 1979). CBC data show roughly cyclical fluctuations (Figure 3), which might correlate with the North Atlantic Oscillation, with higher counts following milder summers on Sable Island (I.A. McLaren unpub. data).

As also noted above, summer censuses show a clear increase from 1967–1979 (1250–3300 individuals) to 1995 (3400 individuals), and again to 1998 (5900 individuals) and 2006 (6700 individuals). Hence, based upon summer counts, the breeding population nearly doubled during the 10–year period from 1995 to 2006. CBC totals also show a slight but statistically significant increase over the past two decades of about one bird per count per decade, though this trend might have levelled off in the past decade (Figure 3). Again, however, CBC data for this bird are sparse and subject to various observer biases that are hard to evaluate, so these results should be viewed cautiously.

Overall, both summer censuses and CBC data suggest that the population increased in the 1990s, but may have levelled off in the past decade.

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Rescue effect

Because Ipswich sparrows breed exclusively on Sable Island, and their differences from other races of Savannah Sparrow may be specific adaptations to life on outer coastal dunes for which these other races are poorly suited, there is no chance of rescue from other populations.

Figure 3. Mean number of Ipswich sparrows seen on the wintering grounds, based on Christmas Bird Count count circles that reported them. Large dots are for the past 20 years, for which the linear trend (solid line) is significant (y=0.10x–201.89, F1,18=7.32, P=0.0145, R2=0.29). Filled large dots are for the past 10 years, for which the linear trend (dashed line) is indistinguishable from zero (y=0.02x–41.48, F1,8=0.03, P=0.86, R2=0.00).

Chart showing mean number of Ipswich sparrows seen on the wintering grounds, based on Christmas Bird Count count circles that reported them.

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Limiting Factors and Threats

Although the previous status report underestimated the carrying capacity of the Ipswich sparrow’s breeding habitat, vegetated habitat on the island is still limited to about 1000 ha (Stobo and McLaren 1975). This limitation, along with the concentration of the population in such a small area, make this bird highly vulnerable to any localized threats.

Nonetheless, there is no direct evidence that the population is under any immediate threats, apart from the likely continuing destruction of its wintering habitat and the possibility of harsh weather, particularly during migration and winter, periods for which there is some evidence for effects of weather on the population (see above). Evidence collected since the previous status report fails to support some of the other threats posited there.

Because overwinter survival appears to be the most important limiting factor to the population, any threats to winter habitat might have a particularly severe effect on the population. Protection of dune habitats along the Atlantic coast continues to improve, but is not directed specifically at sparrow habitat, and may in some cases have adverse effects on it. For example, artificial barrier dunes may accelerate plant succession (Schroeder et al. 1976), potentially beyond the dense grassy stages apparently preferred by Ipswich sparrows (Stobo and McLaren 1971).

Harsh weather, especially during migration or winter, as noted above, can have dramatic effects on the population size, because of the population’s small distribution. The harsh winter of 1977–1978 presumably accounted for a crash in the population over that season (McLaren 1979), although the population rapidly recovered, thanks to its high reproductive rate (Horn 1999). Climate change is expected to result in increases in both the frequency and intensity of Atlantic storms. Moreover, because Sable Island is a low–lying sand island, the entire island is vulnerable to the rises in sea–level that are projected to occur as a result of climate change.

Predation was mentioned in earlier status reports as a potential threat, but, while predation rates of Ipswich sparrows vary across years, they are typically low for a ground–nesting passerine. Gull populations on Sable Island appear to have been stable, at least when they were censussed between 1970 and 1997, and other potential avian predators occur only occasionally and in small numbers (Horn 1999). Introduction of mammalian predators is a serious threat for most island birds, but is unlikely to occur on Sable Island given its great distance from the mainland and its restricted access. Historically, the population survived numerous cats and foxes on the island for many years (Elliot 1968).

The previous status report suggested that hybridization with mainland Savannah Sparrows and inbreeding among the birds on the island might be threats to the genetic viability of the population (Horn 1999). As noted above, however, mitochrondrial DNA studies have since found evidence that gene flow between the island and mainland is quite restricted (Mockford et al. 2003; Zink et al. 2005).

Various human activities on Sable Island could be threats to Ipswich sparrows if they were not tightly controlled. Construction of any structures on Sable Island could potentially destroy sparrow habitat, both directly and by increasing the chance of erosion well beyond project footprints, but such activities are under rigorous permitting regulations. Inadvertent or intentional introduction of mammalian predators and non–native, potentially invasive plants, has often occurred on Sable Island in the past, but with today’s tight regulations on travel to the island, such introductions seem unlikely. As well, there is no evidence that grazing or trampling by horses destroys sparrow habitat on Sable Island.

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Special Significance of the Species

Though not a true Canadian endemic species because it winters in the U.S., the Ipswich sparrow is perhaps Canada’s best–known, range–restricted breeding songbird. Its description in bird guides introduces Sable Island to naturalists across North America. Seeking it in winter is one of the highlights of the winter birding season along the Atlantic coast (McLaren and Horn 2006), and since its discovery it has been a central example in the ongoing controversy over species level taxonomy and systematics in birds (Remsen 2005; McLaren and Horn 2006; Zink 2006). Though not studied, it may also contribute to Sable Island’s ecology (e.g., through seed dispersal or control of insect populations).

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Existing Protection or Other Status Designations

The Ipswich sparrow is protected by the Canadian Migratory Birds Convention Act, 1994 and the US Migratory Bird Treaty Act, 1918. COSEWIC assessed this species as Special Concern in May 2000, and it is currently federally listed in Canada as Special Concern in Schedule 1 of the Species at Risk Act, which requires creation of a management plan. It is not listed provincially in Nova Scotia, nor is it listed federally in the United States, but it is listed as Special Concern in Connecticut and Threatened in Rhode Island and New Jersey.

The bird’s status rank in Nova Scotia is S1S2B (Imperiled to Critically Imperiled). Perhaps because of its subspecific status, its designations at the provincial and state level are not thoroughly listed by NatureServe, which lists its Rounded Global Status as T2 (Imperiled), its US National Status as N1N (Critically Imperiled), and its Canadian National Status as N1B (Critically Imperiled; NatureServe 2008). Moreover, a search of species lists given by wildlife department websites of individual states shows that some status ranks incorrectly imply extralimital breeding (with a Breeding Status Qualifier of “B”), no doubt because the population has not been distinguished from local populations of Savannah Sparrows. Specifically, the bird is appropriately listed as S1N (Critically Imperiled) in Connecticut, but listed as S3B (Vulnerable) in New Jersey and S1B, S5N (Secure to Critically Imperiled) in North Carolina, where, in a ranking system specific to that state, it is also considered Significantly Rare.

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Technical Summary

Passerculus sandwichensis princeps

Savannah Sparrow princeps subspecies – Bruant des prés de la sous–espèce princeps

Range of Occurrence in Canada: Nova Scotia

Demographic Information

Generation time 1.5 yrs
Is there an observed continuing decline in number of mature individuals? No
Estimated percent of continuing decline in total number of mature individuals within 5 years Not applicable
Estimated percent increase in total number of mature
individuals over the last 10 years. – Breeding population
increased (nearly doubled) from 1995 to 2006.
Population size is likely influenced by climate; recent
increases are probably due to recent mild winters
(see Population sizes and trends).
Increased; but difficult to quantify
Projected percent change in total number of mature individuals over the next 10 years. Unknown
Inferred percent change in total number of mature
individuals over any 10–year period, over a time
period including both the past and the future. – see Population sizes and trends
Relatively stable, barring localized catastrophic events
Are the causes of the decline clearly reversible and understood and ceased? Not applicable
Are there extreme fluctuations in number of mature individuals? No

Extent and Occupancy Information

Estimated extent of occurrence – see Canadian range 90 km²
Index of area of occupancy (IAO) – based upon 2x2 grid; see Canadian range 80 km²
Is the total population severely fragmented? No
Number of “locations” One
Is there an observed continuing decline in extent of
occurrence? – stable
No
Is there an observed continuing decline in index of area of
occupancy? – stable
No
Is there an observed continuing decline in number of
populations? – stable
No
Is there an observed continuing decline in number of
locations? – stable
No
Is there an observed continuing decline in area, extent
and/or quality of habitat? – breeding habitat is stable,
though declines are believed occurring on wintering
grounds; see Habitat trends
No (breeding grounds)
Yes (wintering grounds)
Are there extreme fluctuations in number of populations? No
Are there extreme fluctuations in number of locations? 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 population

Population N Mature Individuals
Canada 6000
Total 6000

Quantitative Analysis

Probability of extinction in the wild. Not done

Threats (actual or imminent, to populations or habitats)

Destruction of winter habitat, harsh weather during migration and wintering. Restriction to breeding at a single island location exposes it to catastrophic events (e.g., hurricanes).

Rescue Effect (immigration from outside Canada)

Status of outside population(s)? USA: No outside population
Is immigration known or possible? No
Would immigrants be adapted to survive in Canada? Not applicable
Is there sufficient habitat for immigrants in Canada? Not applicable
Is rescue from outside populations likely? No

Current Status

COSEWIC: Special Concern (November 2009)

Status and Reasons for Designation

Status: Special Concern
Alpha–numeric code: Not applicable

Reasons for designation:
This songbird is largely restricted to the sandy dune systems of Sable Island, NS. The population has increased over recent decades and now shows signs of stability because the island has reached carrying capacity. The bird is not prone to human disturbance because the breeding location is well protected. The subspecies is also multi–brooded and currently experiences good nesting success, which confers good reproductive potential to cope with potential catastrophic events. Nevertheless, its breeding range is restricted to a very small area of Canada, and it has a relatively small population. It is also exposed to ongoing threats associated with development of its shoreline wintering habitat in the eastern U.S., and is vulnerable to sea–level rise and increasing frequency and intensity of Atlantic storms that are projected to occur as a result of climate change.

Applicability of Criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable – population has been relatively stable over the past 10 years and shows signs of modest increase over the past 20 years.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable – although extent of occurrence is <5000 km², area of occupancy is <500 km², and population is restricted to <5 locations, there have been no declines or extreme fluctuations in extent of occurrence, area of occupancy, habitat quality, or number of individuals.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable – although the population is <10,000 mature individuals, there is no evidence for a decline in population size.

Criterion D (Very Small or Restricted Total Population): Not applicable – although the population occurs in <5 locations, it is not prone to the effects of human activities or stochastic events that can be expected within a very short time period, as evidenced by its long history of persistence, coupled with a currently good reproductive capacity that would be expected to buffer the population in the foreseeable future.

Criterion E (Quantitative Analysis): Not done.

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Acknowledgements and Authorities Consulted

Acknowledgements

Catherine Dale and Ian McLaren provided invaluable access to unpublished data and manuscripts. Peter Blancher, Dick Cannings, Theresa Fowler, Vicki Friesen, Tony Gaston, Darren Irwin, Richard Knapton, Marty Leonard, Jon McCracken, Julie Paquet, and Peter Thomas gave valuable feedback and editorial assistance on earlier drafts of this report. Thanks to Ian McLaren for permission to use the cover photograph of an Ipswich sparrow. Environment Canada provided funding for the preparation of this report.

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Authorities consulted

  • Blaney, Sean. Assistant Director, Atlantic Canada Conservation Date Centre, Sackville, NB.
  • Boates, Sherman. Wildlife Manager, Biodiversity, NS Department of Natural Resources, Kentville, NS.
  • Boyne, Andrew. Wildlife Biologist, Species at Risk, Environment Canada – Ecosystem Conservation, Dartmouth, NS.
  • Dale, Catherine. Ph.D. Candidate, Department of Biology, Queens University, Kingston, ON.
  • Filion, Alain. Scientific and Geomatics Project Officer, COSEWIC Secretariat, Environment Canada, Ottawa, ON.
  • Goulet, Gloria. Coordinator – Aborginal Traditional Knowledge, COSEWIC Secretariat, Environment Canada, Ottawa, ON.
  • McLaren, Ian. Professor Emeritus, Department of Biology, Dalhousie University, Halifax, NS.

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Information Sources

Bernd–Cohen, T. and M. Gordon. 1998. State Coastal Program Effectiveness in Protecting Natural Beaches, Dunes, Bluffs, and Rocky Shores. Coastal Management 27:187–217.

Beson, K. 1998. A Conservation Strategy for Sable Island. Can. Wildlife Service, Atlantic Region, Dartmouth, NS. [Accessed April 2009]

Blaney, S., per. comm. 2008. Email correspondence to A.G. Horn. November 2008. Assistant Director, Atlantic Canada Conservation Date Centre, Sackville, NB.

Byrne, M.L. and S.B. McCann. 1995. The dunescape of Sable Island. Canadian Geographer 39:363–368.

Dale, C. 2007. Links between the winter and breeding seasons in a short–distance migrant, the Ipswich sparrow (Passerculus sandwichensis princeps). M.Sc. thesis, Dalhousie University, Halifax, Nova Scotia.

Dale, C., pers. comm. 2008. Email correspondence to A.G. Horn. October 2008. Ph.D. candidate, Department of Biology, Queens University, Kingston, Ontario.

Davis, B.C. 2003. Inventory, classification, and analysis of Special Management Areas associated with U.S. coastal programs. Coastal Management 31:339–354.

Elliot, J.J. 1968. Passerculus princeps (Maynard), Ipswich Sparrow. pp. 657–675 in A.C. Bent (O.L. Austin Jr., ed.) Life histories of North American cardinals, grosbeaks, buntings, towhees, finches, sparrows, and allies. Bulletin of the United States National Museum 237, Pt. 2.

Erskine, A.J. 1992. Atlas of Breeding Birds of the Maritime Provinces. Nimbus and the Nova Scotia Museum, Halifax, Nova Scotia.

Freedman, B. 1996. Airphoto assessment of changes in plant cover on Sable Island, Nova Scotia. Unpublished report prepared for Canadian Wildlife Service, Atlantic Region, Dartmouth, N.S.

Gray, D.H. 1992. Where has Sable Island been for the past 200 years? CISM Journal ACSGC 46:265–275.

Hailman, J.P. 1958. Behavior notes on the Ipswich sparrow. Bird–Banding 29:241–244.

Horn, A.G. 1999. Updated status report on the Ipswich Sparrow Passerculus sandwichensis princeps in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa.

Horn, A.G. 2007. Preliminary report on the 2006 census of Ipswich sparrows. Unpublished report for the Sable Island Preservation Trust, Halifax, Nova Scotia.

Maritimes Breeding Bird Atlas (MBBA). 2008. The Maritime Breeding Bird Atlas: Species and Effort Maps. [Accessed November 2008]

McCann, S.B. and M.L. Byrne. 1994. Dune morphology and the evolution of Sable Island, Nova Scotia, in historic times. Physical Geography 15:342–357.

McLaren, I.A. 1979. Status report on the Ipswich Sparrow Passerculus sandwichensis princeps in Canada. Unpublished report prepared for the Canadian Wildlife Service, Atlantic Region, Dartmouth, NS.

McLaren, I.A. and A.G. Horn. 2006. The Ipswich Sparrow: past, present and future. Birding 38:52–59.

Mockford, S., A.G. Horn, J.M. Wright, and M. Leonard. 2003. An examination of genetic variation between typical Savannah Sparrow on the Nova Scotia mainland and Ipswich Sparrow using mitochondrial DNA. Unpublished report prepared for the Canadian Wildlife Service, Atlantic Region, Dartmouth, NS.

NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 4.7. NatureServe, Arlington, Virginia. [Accessed November 2008].

Potter, P.E. 1974. Breeding behavior of Savannah Sparrows in southeastern Michigan. Jack–Pine Warbler 52:50–63.

Remsen, J.V., Jr. 2005. Pattern, process, and rigor meet classification. Auk 122:403–413.

Rising, J.D. 2001. Geographic variation in size and shape of Savannah Sparrows (Passerculus sandwichensis). Cooper Ornithological Society, Camarillo, CA, USA.

Rising, J.D. 2007. Names subspecies and their significance in contemporary ornithology. Ornithological Monographs 63:45–54.

Ross, H.A. 1979. Determinants of fitness in the Ipswich Sparrow. Ph.D. dissertation, Dalhousie University, Halifax, Nova Scotia.

Ross, H.A. 1980a. Growth of nestling Ipswich Sparrows in relation to season, habitat, brood size, and parental age. Auk 97:721–732.

Ross, H.A. 1980b. The reproductive rates of yearling and older Ipswich Sparrows, Passerculus sandwichensis princeps. Canadian Journal of Zoology 58:1557–1563.

Ross, H.A. and I.A. McLaren. 1981. Lack of differential survival among young Ipswich Sparrows. Auk 98:495–502.

Schroeder, P.M., R. Dolan, and B.P. Hayden. 1976. Vegetation changes associated with barrier–dune construction on the outer banks of North Carolina. Environmental Management 1:105–114.

Smith, S.J., Z. Lucas, and W.T. Stobo. 2003. Estimate of the Ipswich Sparrow population on Sable Island, Nova Scotia, in 1998, using a random–transect survey design. Canadian Journal of Zoology 81:771–779.

Stalter, R. and E.E. Lamont. 2006. Historical and extant flora of Sable Island, Nova Scotia. Journal of the Torrey Botanical Society 133:363–374.

Stobo, W.T. and I.A. McLaren. 1971. Late winter distribution of the Ipswich Sparrow. American Birds 25:941–944.

Stobo, W.T. and I.A. McLaren. 1975. The Ipswich Sparrow. Nova Scotia Institute of Science, Halifax.

Temple, M. 1996. The role of density in the natural regulation of the Ipswich Sparrow (Passerculus sandwichensis princeps). Unpublished ms, Dalhousie University, Halifax, Nova Scotia.

Temple, M. 2000. Microsatellite analysis of extra–pair fertilization in the Ipswich Sparrow (Passerculus sandwichensis princeps). Unpublished M.Sc. thesis, Dalhousie University, Halifax, Nova Scotia.

Watts, B.D. 1999. Partners in Flight Mid–Atlantic Coastal Plain Bird Conservation Plan (Physiographic Area #44). American Bird Conservancy, The Plains, Virginia.

Weatherhead, P.J. 1979. Ecological correlates of monogamy in tundra–breeding Savannah Sparrows. Auk 96:391–401.

Welsh, D.A. 1976. Population, behavioural and grazing ecology of the horses of Sable Island. Unpubl. Ph.D. thesis, Dalhousie University, Halifax, N.S.

Wheelwright, N.T. and J.D. Rising. 2008. Savannah Sparrow (Passerculus sandwichensis). In The Birds of North America, No. 45 (A. Poole and F. Gill, Eds.). The Academy of Natural Sciences, Philadelphia, and AOU, Washington, D.C.

Zink, R.M., J.D. Rising, S. Mockford, A.G. Horn, J.M. Wright, M. Leonard, and M.C. Westberg. 2005. Mitochondrial DNA Variation, Species Limits, and Rapid Evolution of Plumage Coloration and Size in the Savannah Sparrow. Condor 107:21–28.

Zink, R.M. 2006. Rigor and species concepts. Auk 123:887–891.

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Biographical Summary of Report Writer

Andrew Gregg Horn grew up in Cambridge, Massachusetts, earned his B.Sc. at Cornell University in 1981, and did his Ph.D. in Zoology at University of Toronto on song complexity in Western Meadowlarks Sturnella neglecta. During post–doctoral work at University of Cambridge, Queens University, and Agriculture Canada, he studied various aspects of parent–offspring interactions and acoustic communication in birds, work he continues as a Research Adjunct at Dalhousie University. He has also conducted various projects in avian monitoring and assessment, including several on Ipswich sparrows. He is the first author of several draft status reports and recovery plans, including the previous status report and the Canadian management plan for the Ipswich sparrow.