Food Habits of Bald Eagles Breeding in the Arizona Desert

-of 1814 foraging attempts, prey captures, or nest deliveries by Bald Eagles (Haliaeetus Zeucocephalus) in 14 Arizona breeding areas during 1983-1985, 1471 observations were identifiable to at least class: fish (76%), mammal (18%), bird (4%), and reptile/ amphibian (2%). Forty-five species were recorded: catfish (Zctalurus punctatus, fylodictis olivaris), suckers (Catostomus ins&k, C. clarki), and carp (Cyprinus carpio) were most common. Mean population dietary heterogeneity was 2.03 (SD = 0.43). During 1983-1985, 22 successful sites had a wider dietary breadth than nine unsuccessful ones (3.73 vs 1.92). Fish and mammal classes varied by month (P < 0.001) and breeding area (P < 0.001) and were negatively correlated (R = -0.993, P = 0.001). Of 484 discrete foraging locations, only four (~1%) were frequented in more than one year. Within-season shifts in foraging locations were typical within breeding areas to accommodate changing prey availability. Foraging activity varied hourly and among prey classes, peaking 08:0&10:00 and 16:0019:00 h MST (P < 0.001). Perches east (NE-E-SE) of foraging sites were used more often before 13:00 h MST (59.3%, N = 118), while perches west (SW-W-NW) were used more often after 13:00 h (58.4%, N = 113; P = 0.013). Most foraging occurred near shore in shallow river waters. The mean straight-line distance between Verde River nest sites was 14.4 km (SD = 3.5) with a ratio of river: straight-line distance of 1.4: 1. Opportunistic and breeding area-specific foraging was evident throughout the population. Received 2 May 1994, accepted 11 Nov. 1994. Bald Eagles (Huliaeetus leucocephalus) typically nest along marine coastlines and large interior lakes and rivers where they have evolved as a fish-eating sea eagle. Food habits have been studied extensively throughout the Bald Eagle’s range (Grubb and Hensel 1978, McEwan and Hirth 1980, Cash et al. 1985, Brown et al. 1991); their opportunistic foraging habits are well known (Brown and Amadon 1968). Hunt et al. (1992) summarized the progressive accumulation of food habits data in Arizona through the mostly unpublished research of Rubink and Podborny (1976), Hildebrandt (1981), Haywood and Ohmart (1986) and Grubb (unpubl. data). The purpose of this paper is to document more fully the food habits results of interagency cooperative research led by the USDA Forest Service on Bald Eagles breeding in central Arizona during 19831985 (Grubb, unpubl. data), which was an extension and expansion of previous Arizona studies. In this study observations of food habits (foraging attempts, prey captures, nest deliveries), supplemented by prey remains collected from nests, were used to determine dietary composition USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, 2500 S. Pine Knoll Drive, Flagstaff, Arizona 86001,