Ferruginous hawk (Buteo regalis) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

Numerous factors are thought to limit populations of the Ferruginous Hawk. First, the range of the species has been reduced by 50% in Canada (Schmutz et al. 1992). Because hawks that die or vacate territories are replaced quickly by new individuals, Schmutz (1995) deduced that available habitat was saturated. Maintaining prairie grassland was identified as a priority in the recovery plan (Schmutz et al. 1994). Second, as for all raptors, there is a strong relationship between Ferruginous Hawk populations and their prey base (Newton 1979). In Canadian populations, the main prey is ground squirrels, and hawk reproduction is strongly tied to ground squirrel population fluctuations (Downey et al. 2004, Houston and Zazelenchuk 2006). It is possible that although historically populations of Ferruginous Hawks fluctuated with changes in ground squirrel populations, 1) the limited remaining grassland habitat preferred by ground squirrels provides a much-reduced prey base for hawks and 2) the magnitude and spatial scale of fluctuations in ground squirrel populations may be greater due to anthropogenic factors, though there is no firm evidence for this (B. Downey, pers. comm.). The hawk population that remains may be particularly vulnerable to disturbance at nests by humans. Other factors recently identified as possibly contributing to declines in Ferruginous Hawk populations are climate change, and oil and gas pipelines (Stepnisky et al. 2004; Downey 2005).