Anthropogenic effects on winter behavior of ferruginous hawks

Little information is known about the ecology of ferruginous hawks (Buteo regalis) in winter versus the breeding season and less about how the species adapts to fragmented grassland habitats. Accordingly, we studied the behavior of 38 radiotagged ferruginous hawks during 3 winters from 1992 to 1995. We used 2 adjacent sites in Colorado that were characterized by low and high levels of anthropogenic influence and habitat fragmentation: the Rocky Mountain Arsenal National Wildlife Refuge (RMANWR; low-level influence), and several adjacent Denver suburbs (high-level influence). Relative abundance of ferruginous hawks differed by treatment area and year (P < 0.001); hawks were most numerous where black-tailed prairie dogs (Cynomys ludovicianus) were most plentiful. Daily Minimum Convex Polygon (MCP) home range areas did not differ (P = 0.28) for RMANWR (x?? = 4.71 km2, SE = 1.33, n = 25) and suburban hawks (x?? = 2.30 km2, SE = 0.50, n = 13). The number of perches occupied per day between the sites was not different (P = 0.14), but hawks at RMANWR used pole and ground perches more frequently and for a greater portion of the daily time budget (P < 0.05). Hawks at RMANWR spent less time roosting after sunrise (x?? = 61 min) than did suburban hawks (x?? = 138 min; P = 0.004) and spent less time roosting during the day (RMANWR = 100 min; suburb = 189 min; P = 0.009). Prey acquisition and associated intra- and interspecific interactions were not different (P > 0.05) at RMANWR and suburban sites. Ferruginous hawks appear to modify their behavior in fragmented, largely human-altered habitats, provided some foraging habitats with adequate populations of suitable prey species are present.