FOOD-HABITS OF BALD EAGLES BREEDING IN THE ARIZONA DESERT

Of 1814 foraging attempts, prey captures, or nest deliveries by Bald Eagles (Haliaeetus leucocephalus) 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 (Ictalurus punctatus, Pylodictis olivaris), suckers (Catosromus insignis, 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 08:00-10:00 and 16:00-19:00 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.