Susceptibility to Predation Varies with Body Mass, Foraging Niche, and Anti-Predator Responses among Bird Species

Simple Summary Predation can have a major impact on animal populations, and yet the factors that affect susceptibility to predation among species are poorly understood given that predation rate is difficult to measure in the field. Using estimates of predation rates from a large number of published radio-tracking studies in birds, I examined the general expectation that species facing fewer predators or those with effective anti-predator responses experience lower predation rates. I obtained 393 estimates of predation rates from 129 species, and the results generally supported the prediction. To obtain a fuller picture, more research is needed to broaden the range of species and habitats included in radio-tracking studies.Abstract Predation is a major source of mortality for many avian species. Species that face more predators, and those with less effective anti-predator responses, are presumably more likely to die from predation over time. Predation rate, as a measure of susceptibility to predation, is difficult to measure in the field. Radio-tracking studies, however, allow researchers to determine the time and cause of death of marked individuals, making it possible to estimate predation rate. I used estimates of predation rates from a large number of published radio-tracking studies in birds to assess in a phylogenetic framework the effect of several potential determinants. I obtained 393 estimates of predation rates from 129 species. Predation rates were lower in areas with fewer predators, such as islands and aquatic habitats, and for species with fewer potential predators, such as larger species. The predation rate was also lower for prey species with effective anti-predator responses, such as those that forage in flocks. Radio-tracking studies provide a unique opportunity to estimate overall predation rate in the field. Broadening the range of species and the range of habitats involved in such studies will help to further elucidate the factors that affect susceptibility to predation.