McCown's longspur (Calcarius mccownii) COSEWIC assessment and status report: chapter 5

Habitat

Breeding habitat requirements

McCown's Longspurs breed in open, arid grasslands with dry, sandy soil (Stewart 1975, Wershler et al. 1991), little litter accumulation (Felske 1971), and sparse low vegetation (With 1994a), such as that provided by shortgrass prairie or heavily grazed mixed-grass prairie (Dechant et al. 1999). Nesting areas are dominated by blue grama grass (Bouteloua gracilis) and buffalo grass (Buchloe dactyoides), which grow to a maximum height of 0.5 m (Brown 1985) and are often interspersed with cactus (e.g., Opuntia sp.) and bare ground (With 1994a).

Responses to grazing management

McCown's Longspurs in southern Alberta are detected in higher numbers on native grasslands that are grazed on a continuous basis (April through October) than those managed with complementary or rotational grazing (Prescott and Wagner 1996). This is likely related to range quality, as the latter grazing regimes result in higher, denser vegetation than is preferred by this species. Heavily grazed pasture may best approximate the historical shortgrass prairie in which this species evolved (With 1994a) and may explain why several studies have recorded McCown's Longspurs on moderately to heavily grazed grasslands but not ungrazed sites (Maher 1973, Kantrud and Kologiski 1982, Wershler et al. 1991, Sutter 1997).

Attraction to cultivated fields

Even within grassed landscapes, McCown's Longspurs are often detected on cultivated lands (McMaster and Davis 1998, Dale et al. 2005) such as conventionally tilled wheat fields (Martin and Forsyth 2003) and fallow fields (Dale et al. 2005). Survey data suggest that this attraction to agricultural land is not only a response to habitat saturation (S. Davis, pers. comm.), but may also be because the structural similarities between cultivated lands and native grasslands make differentiation between the two habitats difficult for birds settling in spring (e.g., Lloyd and Martin 2005). This is of concern because breeding success may be poorer in cultivated fields than in native habitats and there is a greater chance of direct exposure to agricultural pesticides (Martin and Forsyth 2003). Thus, cultivated fields may be an "ecological trap" for McCown's Longspurs (Best 1986, Martin and Forsyth 2003). It also appears to be a relatively recent phenomenon, as historically McCown's Longspurs avoided cultivation (DuBois 1937, Mickey 1943).

Wintering habitat

On their winter range, McCown's Longspurs are most abundant on lightly grazed shortgrass pastures dominated by Bouteloua-Buchloe. In Mexico, their winter habitat includes plateaus and deserts (Peterson and Chalif 1973, With 1994a).

Microhabitat requirements

McCown's Longspurs build their nests on barren south or southwestern facing hillsides (Felske 1971) with nests oriented northward (With and Webb 1993). Nests are built in a depression in the ground and are often placed near some sort of vegetation, such as a clump of grass or a shrub (With 1994b). 

Annual variation in precipitation may affect general habitat suitability. Prescott and Wagner (1996) suggested that the decline in numbers of McCown's Longspurs detected over the duration of their study could, in part, be due to above average precipitation that resulted in increased vegetation growth. Conversely, drought conditions in the early 2000s were correlated with an upsurge in numbers of McCown's Longspurs detected at Suffield National Wildlife Area in Alberta (B. Dale, pers. comm.).

Habitat trends

Grasslands have been heavily impacted by agriculture. By 1991, approximately 75% of the original native prairie in Canada had been converted to agricultural or other land uses (Statistics Canada 1992, Samson and Knopf 1994). Since then, habitat loss has continued at an estimated rate of 1%/year (Statistics Canada1997), although it is not clear what proportion of this habitat is suitable for McCown's Longspurs. The recent observations of McCown's Longspurs in cultivated fields (McMaster and Davies 1998; Martin and Forsyth 2003) suggests, however, that they may be partially responding to habitat loss and land use changes because historically they avoided cultivated land (DuBois 1937, Mickey 1943).

Fire suppression may have also reduced the quality of habitat for McCown's Longspurs. Historically, native shortgrass prairie was subjected to frequent wildfires, along with periodic intense grazing by indigenous herbivores such as bison (Bison bison; Knopf 1994). Both types of disturbance resulted in habitat with patches of bare ground, a factor associated with higher numbers of McCown's Longspurs (Martin and Forsyth 2003). Fire suppression has been suggested as one possible reason for declines in the distribution and abundance of McCown's Longspurs (Oberholser 1974).

Habitat protection/ownership

In Alberta, approximately 40,000 km² of native grassland remains and 23,606 km²is under Crown ownership. Although most of this land is not considered protected, the Crown has been somewhat successful in preventing permanent loss of native grassland habitat. Crown land represents only 24% of the Alberta Grassland Natural Region but has 56% of the total remaining native grasslands. The majority of the Crown lands are used for grazing leases or community pastures. Approximately 2% of the native grasslands are officially protected. Some of the larger protected lands that have McCown's Longspurs include the Suffield National Wildlife Area (458.7 km²), the Onefour Heritage Rangeland Natural Area (92 km²), and the Twin River Heritage Rangeland Natural Area (150 km², Alberta Sustainable Resource Development 2000).

In Saskatchewan, just over 32% of the remaining grassland is protected in conservation areas including national and provincial parks, Nature Conservancy land, migratory bird sanctuaries and wildlife refuges, Ramsar sites, ecological reserves, land under the Wildlife Habitat Protection Act and PFRA community pastures. The total land protected is 22,636 km² or 9.4% of the Saskatchewan Prairie Ecozone (Gauthier et al. 2002). The most important lands to protect for McCown's Longspurs are those in the southwestern corner of the province, south of the South Saskatchewan River and west of Regina.

In addition, 4,415.5 km² of private land has been enrolled in the Permanent Cover Program (PCP) in Alberta, Saskatchewan, and Manitoba (McMaster and Davis 1998). The potential exists to modify some of these PCP sites to create suitable breeding habitat for McCown's Longspurs.

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