PLUMAGE BRIGHTNESS OF PREY INCREASES PREDATION RISK: AN AMONG-SPECIES COMPARISON

Abstract

The risk to passerine birds of predation by the Sparrowhawk (Accipiter nisus) was analyzed with respect to differences in plumage brightness, body mass, and density of prey species, while taking into account phylogenetic relatedness of species. Data were collected from published sources in five separate areas along a south–north geographical gradient in Finland and consisted of 2214 prey remains collected from Sparrowhawk nests. Prey plumage brightness was the most important factor determining vulnerability to predation. In adults, male brightness was more important than female brightness in explaining prey vulnerability. Prey abundance did not affect the relationship between predation vulnerability and plumage brightness, because both rare and common species with bright plumage suffered higher predation. Prey species with large body mass were more vulnerable to predation in northern Finland, suggesting that in northern harsh conditions, Sparrowhawks may prefer large prey in order to fulfill their daily energy requirements. Our analyses provide evidence that predation may impose viability costs on sexually selected traits such as plumage brightness and body size.