干旱区生态环境知识资源中心

We located two populations of endangered Aplomado Falcons (Falcofemmalis) in desert grasslands in north-central Mexico in 1992. During spring 1993, we quantified breeding success, habitat use, and prey selection by the easternmost population, which is located 40 km from the United States. We captured 17 individuals (one subadult male, seven adult males, three subadult females, six adult females) and placed tail-mounted radio transmitters on 15 of them. Females weighed 50% more, had tails 9% longer, and had wing chords 11% longer than males. Breeding season ranges of six radio-tagged individuals monitored more than 100 d ranged from 3.3-21.4 km(2). Woody plant density ranged from 11.2-139.5/ha and percentage of ground-cover ranged from 28.9-69.5% in ten falcon territories. Six of seven nests were in yuccas (Yucca elata, Y. torreyi). Seven nesting pairs had a mean clutch size of 2.6, mean hatching success of 1.6, and a mean fledging success of 0.6. We identified 87 prey items from pellets, prey remains, and observed successful hunts; 82 were avian and 5 were insect. Meadowlarks (Sturnella spp.) were most abundant on potential prey transects and in the diet of Aplomado Falcons. Brown-headed Cowbirds (Molothrus ater), Greater Roadrunners (Geococcyx californianus) and hummingbirds (Trochilidae) were identified in diets, but were not detected on transects.