mesopredator release The South Island piopio Chatham rail New Zealand merganser Lyall's wren New Zealand lesser short-tailed bats mammals predator domestic mammal
On islands, birds can contribute as much as 60% of a cat's diet. In nearly all cases, the cat cannot be identified as the sole cause for reducing the numbers of island birds, and in some instances, eradication of cats has caused a "mesopredator release" effect; where the suppression of top carnivores creates an abundance of smaller predators that cause a severe decline in their shared prey. Domestic cats are a contributing factor to the decline of many species, a factor that has ultimately led, in some cases, to extinction. The South Island piopio, Chatham rail, and the New Zealand merganser are a few from a long list, with the most extreme case being the flightless Lyall's wren, which was driven to extinction only a few years after its discovery.
One feral cat in New Zealand killed 102 New Zealand lesser short-tailed bats in seven days. In the US, feral and free-ranging domestic cats kill an estimated 6.3 – 22.3 billion mammals annually.
