Control of rabbits to protect island birds from cat predation

Both introduced predators (e.g. domestic cats) and introduced small grazers (e.g. rabbits) are harmful to many island vertebrate species. The effects of cats on indigenous species are direct (predation), whereas the most obvi ous effects of rabbits are often indirect and in the longer term. Thus, in situations where both cats and rabbits are present, priority is frequently given to control of cats. However, the presence of rabbits can allow an inc reased predator population which can lead to extinction of the indigenous a nd less well adapted prey species, and increase the difficulty of predator control. Through a mathematical model, we show that control of introduced p rey facilitates the control of the introduced predator population. Moreover , predator control may fail to protect the indigenous prey if control of th e introduced prey is not undertaken simultaneously. Therefore, control of b oth introduced species is the best strategy. (C) 1999 Elsevier Science Ltd. All rights reserved.