Abundance and occupancy of the western yellow-billed cuckoo (Coccyzus americanus) in Sonora, Mexico

Abstract

Unveiling factors that determine abundance and distribution of endangered wildlife species has important implications for their conservation across international boundaries. For instance, the Western Distinct Population (as defined by the U.S. Fish and Wildlife Service) of the yellow-billed cuckoo Coccyzus americanus (Linnaeus, 1758) has disappeared in most of the species’ range across western United States and southwestern Canada but little is known about the conservation status at the southern edge of its breeding distribution in Mexico. To fill this information gap, we estimated abundance and occupancy rates of yellow-billed cuckoos using a standard broadcast call survey protocol. We used Bayesian spatial count models to estimate cuckoo population density at survey sites. We used Bayesian hierarchical models to estimate the effects of geography, climate, and vegetation on occupancy rates while accounting for imperfect detection. Mean cuckoo count per transect for all sites was C = 9.00 ± 0.45 cuckoos. Overall cuckoo density was D = 13.18 cuckoos/km2 (SD(D) = 5.61 cuckoos/km2). Overall cuckoo occupancy in Sonora was ψ = 0.538 (95%CrI(ψ) = 0.488–0.600), but showed strong geographic variation. Relatively high occupancy levels suggest yellow-billed cuckoo populations in Sonora may be robust, but they are largely reliant on declining high-tree cover.