CONTRASTING HOME RANGE CHARACTERISTICS AND PREY OF SYMPATRIC HAWKS (BUTEO SPP) NESTING IN THE UPPER COLUMBIA RIVER BASIN

Abstract

Abstract Between 2007 and 2021 we monitored adult hawks (Buteo spp.) nesting in the upper Columbia River Basin of Washington and Oregon using global positioning system (GPS) telemetry on 17 Ferruginous Hawks (B. regalis), 9 Red-tailed Hawks (B. jamaicensis), and 14 Swainson's Hawks (B. swainsoni). Our main objectives were to: (1) provide contemporary home-range estimates using fixes generated by the global positioning system to better inform protective buffers on Buteo ranges in the Columbia River Basin; and (2) describe prey analyzed from pellets collected at 47 Buteo territories. Breeding home ranges (Brownian bridge movement model, 95% isopleths) of Ferruginous Hawks (B. regalis) were substantially larger (x̄ = 378, sx = 133 km2) than those published previously, as were home ranges of Swainson's Hawks (x̄ = 276, sx = 146 km2) and Red-tailed Hawks (x̄ = 28, sx = 12 km2). Diets of Ferruginous Hawks on the study area were dominated (60%) by Northern Pocket Gophers (Thomomys talpoides), whereas Swainson's Hawks primarily (83%) ate grasshoppers (Apote notablis and Melanoplus spp.). Red-tailed Hawks ate a less-specialized diet of reptiles (40%), mammals (38%), and birds (13%). We provide models that show the probable degree of protection afforded by different-sized buffers when applied to species-specific home ranges and core areas for hawks in the Columbia River Basin.