McCown's longspur (Calcarius mccownii) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

Habitat loss and alteration

McCown's Longspurs have a restricted breeding range that has contracted over the past century because of habitat loss and alteration. An estimated 75% of the original native grassland on the Canadian prairies has been lost as a result of human activities (Statistics Canada 1992, Knopf 1994). Only 43% and 21% of native grasslands remain in Alberta and Saskatchewan, respectively, and much of these grasslands are afforded no protection. Although the rate of loss has slowed in the past decade (Statistics Canada 1997), unprotected grasslands continue to be lost to cultivation, residential acreages and urban encroachment, and resource extraction.

Pesticides

Agricultural pesticides may also threaten McCown's Longspurs if they are using cultivated fields. One of the few studies to examine the effects of direct pesticide exposure on grassland birds found that both nestling and adult McCown's Longspurs were susceptible to poisoning from toxaphene, a chemical on the market in the U.S. until the early 1980s that, amongst other things, was used to control grasshoppers in rangeland (McEwen and Ells 1975, P. Mineau, pers. comm.). Congeneric Chestnut-collared Longspurs also had significantly reduced hatching success when exposed to pyrethroid insecticides used for grasshopper control (Johnson et al. 1993). The results of a recent modelling study also showed that the decline of several grassland bird species was associated with the use of agricultural chemicals (Mineau et al. 2005). Although the study did not include McCown's Longspur, it is reasonable to assume that if this species is using cultivated fields, it too, is susceptible to the negative effects of these chemicals (P. Mineau, pers. comm.). 

Attraction to cultivated lands

Recent surveys of breeding birds in Alberta and Saskatchewan have detected a large (20 - 40% of birds) percentage of McCown's Longspurs in cultivated fields, even within grassed landscapes (McMaster and Davis 1998, Martin and Forsyth 2003, Dale et al. 2005). Evidence from work on Chestnut-sided Longspurs suggests that productivity on agricultural lands is generally poorer than in native habitats (Martin and Forsyth 2003), so having such a large number of McCown's Longspurs in cultivated fields is a concern.