Factors Affecting Ferruginous Hawk. Population declines have been attributed to loss of habitat to cultivation, urbanization, grazing, control of small mammals, mining, and fire management, with cultivation the most significant170. Several of the habitat effects are related to prey availability. For example, cultivation leads to replacement of short grasses by taller crops that conceal prey items more effectively. Additionally, nest tree availability is adversely affected by cultivation and some grazing regimes. Olendorff (1993) asserted that grazing with improper stocking levels could also lead to adverse effects to prey items. However in the Thunder Basin, grazing benefits ferruginous hawks by reducing vegetative cover and making prey more visible171. There is no evidence that overutilization is a factor affecting the species. Eggs were once valuable to collectors, but most collecting occurred during the early 1900s, was not likely a key factor in declines, 163 Xxxxxxx and Xxxxxxx (1995) 164 ibid 165 ibid 166 Olendorff (1993) 167 Xxxxxxx and Xxxxxxx (1995) 168 WGFD (2006) 169 ibid 170 Olendorff (1993), Xxxxxxx and Xxxxxxx (1995), Xxxxxxx et al. (1999) 171 Xxxxxxx and Xxxxxxxxx (1983), Xxxxxx and Xxxxxx (1986) as cited in USFS (2001) and no longer appears to be a threat172. Collection for use in falconry is not a threat as ferruginous hawks are rarely used in falconry173. There is no indication that disease is a factor affecting this species. There are few documented instances of nest predation, although ground predators such as coyotes and badgers may pose a threat to ground- nesting ferruginous hawks174. Poisoning and control of prey items (including prairie dogs) can produce local food shortages leading to interruptions in breeding, decreased productivity, and increased susceptibility of breeding ferruginous hawks to human disturbance175. Poisoning, with rodenticides such as zinc phosphide, is used to control rodent populations with minimal impacts to secondary consumers176. However, there is considerable risk of secondary poisoning to non-target avian and mammalian predators and scavengers from the recently approved use of anticoagulant rodenticides such as RozolTM and KaputTM for prairie dog control. Xxxxxxx and Xxxxxxx (1995) and Olendorff (1993) report reduced productivity of nests near active oil and gas xxxxx, although Xxxxxxx et al. (1999) cites a study from Montana that reported no negative impacts on productivity as a result of petroleum development. Collisions with power lines ...
