FOOD HABITS OF BALD EAGLES BREEDING IN THE ARIZONA DESERT

摘要

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 (Catostomus 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.