ANTHROPOGENIC EFFECTS ON WINTER BEHAVIOR OF FERRUGINOUS HAWKS

Little information is known about the ecology of ferruginous hawks (Bu teo regalis) in winter versus tile breeding season and less about how the species adapts to fragmented grassland habitats. Accordingly, we s tudied the behavior of 38 radiotagged ferruginous hawks during 3 winte rs from 1992 to 1995. We used 2 adjacent sites in Colorado that were c haracterized by low and high levels of anthropogenic influence and hab itat fragmentation: the Rocky Mountain Arsenal National Wildlife Refug e RMANWR; low-level influence), and several adjacent Denver suburbs (h igh-level influence). Relative abundance of ferruginous hawks differed by treatment area and year (P < 0.001); hawks were most numerous wher e 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) over bar = 4.71 km(2), SE = 1.33, n = 25) an d suburban hawks ((x) over bar = 2.30 km(2). SE = 0.50, n = 13). The n umber of perches occupied per day between the sites was not different (P = 0.14), but hawks at RMANWR used pole and ground perches more freq uently and for a greater portion of the daily time budget (P < 0.05). Hawks at RMANWR spent less time roosting after sunrise ((x) over bar = 61 min) than did suburban hawks (x) over bar = 138 min: P = 0.004) an d spent less time roosting during the day (RMANWR = 100 min; suburb = 189 min; P = 0.009). Prey acquisition and associated intra-and intersp ecific interactions were not different (P > 0.05) at RMANWR and suburb an sites. Ferruginous hawks appear to modify their behavior in fragmen ted, largely human-altered habitats, provided some foraging habitats w ith adequate populations of suitable prey species are present.