Do Predators Always Capture Substandard Individuals Disproportionately From Prey Populations?

Predators are commonly thought to capture substandard individuals (those in poorer condition than the average individual) in higher than expected proportions, but evidence for this paradigm is scant, biased, and inconsistent. I describe the outcomes of 447 attacks by a trained Red—tailed Hawk (Buteo jamaicensis) on three species of typical mammalian prey (eastern chipmunks, cottontail rabbits, and gray squirrels). A strong correlation existed between the difficulty the hawk had capturing individuals of each species and the difference between the proportions of substandard individuals in the hawk's diet and the prey populations. The degree to which substandard individuals of a particular prey species are taken disproportionately by a predator seems to be a direct function of how difficult it normally is for the predator to capture and kill individuals of that species. A review of other studies shows a similar relationship between vertebrate predators and their prey.