Causes of interspecific variation in susceptibility to cat preda­tion on birds

Generalist mammalian predators hunt for prey in different ways than raptors, often relying on ambush attack. Such differences in predator behavior can have profound effects on susceptibility of different species of prey to predation, but can also modify the behavior of prey. We investigated susceptibility of common birds to predation by domestic cats Felis catus, relying on an extensive data set on prey abundance and prey availability as determined by standardized bird counts. Susceptibility to cat predation for different species of birds was not significantly cor- related with susceptibility to predation by sparrowhawk Accipiter nisus, but with susceptibility to goshawk Accipiter gentilis predation. Susceptibility to goshawk predation was independently pre- dicted by susceptibility to cat and sparrowhawk predation. We cross-validated our estimate of sus- ceptibility to cat predation by showing that the frequency of birds with tail loss increased strongly with susceptibility to cat predation. Male birds were disproportionately preyed upon, especially if having song posts low in the vegetation, and if having short flight distances when singing. Colo- nially breeding species were less susceptible to predation than solitary species. Bird species with high levels of innate immune defense against bacterial infections had high susceptibility to cat predation. These findings suggest that predation by cats has been an important selection pressure affecting anti-predation behavior, sexual display and immune function in common birds.