Factors associated with nest survival of Black-throated Sparrows, desert-breeding nest-site generalists

Black-throated Sparrows (Amphispiza bilineata) are common breeding birds throughout the desert regions of North America and can be considered nest-site generalists. Information about how spatial (e.g., vegetation) and temporal factors influence nest survival of these sparrows is lacking throughout their range. Our objective was to examine the spatial and temporal factors associated with nest survival of Black-throated Sparrows at the nest and nest-patch scales in the predator-rich environment of the northern Chihuahuan Desert of New Mexico. We used a logistic-exposure model fit within a Bayesian framework to model the daily survival probability of Black-throated Sparrow nests. Predation was the leading cause of nest failure, accounting for 86% of failed nests. We found evidence of negative associations between nest survival and both vegetative cover above nests and shrub density within 5 m of nests. We found no support for other habitat covariates, but did find strong evidence that daily survival rate was higher earlier in the breeding season and during the egg-laying stage. A decline in nest survival later in the breeding period may be due to increased predator activity due to warmer ambient temperatures, whereas lower survival during the incubation and nestling stages could be a result of increased activity at nests. A generalist approach to nest-site selection may be an adaptive response to the presence of a diverse assemblage of nest predators that results in the reduced influence of spatial factors on nest survival for Black-throated Sparrows.