Breeding biology and spatial relationships of desert grassland raptors and corvids
AuthorHobbs, Royden J.
Halvorson, William L.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractRed-tailed hawks (Buteo jamaicensis), Swainson's hawks (Buteo swainsoni), great horned owls (Bubo virginiaus), and ravens (Covus corax and C. cryptoleucus) occur sympatrically in desert grasslands in Arizona. Desert grasslands have been invaded by trees since Anglo-American settlement. They may also be subject to greater human disturbance than historically, because of recent increases in illegal immigration along the U.S.-Mexico border. These changes may affect the abundance, diversity, competitive interactions, and reproductive success of raptors and corvids in desert grasslands. I studied raptors and corvids on the Santa Rita Experimental Range (SRER) and Buenos Aires National Wildlife Refuge (BANWR) in southern Arizona. My objectives were to (1) assess how spatial relationships among nesting raptors and corvids affect reproductive success, (2) identify characteristics of the environment selected by members of the assemblage for nest sites and home ranges, (3) identify similarities and differences in nest site and home-range characteristics among species, and (4) investigate how anthropogenic changes in desert grasslands have affected raptors and corvids. Productivity (x̄ [95% CI]) was high for red-tailed hawks on the SRER (1.82 [1.41, 2.23] young per breeding pair [YPB]), but low for all species on the BANWR (great horned owls: 0.96 [0.54, 1.38] YPB; ravens: 1.75 [1.39, 2.10]; red-tailed hawks: 1.04[0.83, 1.24]; Swainson's hawks: 0.91 [0.67, 1.16]) relative to range-wide averages (great horned owls: 1.42 [1.27, 1.56]; ravens: 2.39 [2.70, 3.07]; red-tailed hawks: 1.35 [1.20, 1.50]; Swainson's hawks: 1.34 [1.23, 1.45]). All species on both sites selected nest sites with taller nest trees and greater tree volume than available at random. Swainson's hawks selected home ranges with greater grass volume than available on BANWR. Overlap in habitat use was high among all species, exceeding 54% for nest trees, 80% for nest sites, and 90% for home ranges. Mesquite-dominated desert grasslands seemed to provide high quality habitat for red-tailed hawks on the SRER, but reproductive success for assemblage members on BANWR was poor. We suggest that competition, resulting from high habitat overlap, and human disturbance by illegal immigrants, has depressed raptor and corvid reproductive success on the BANWR.
Degree ProgramGraduate College