Cute Cat

In the Southern Hemisphere - cats are a particular problem in landmasses such as Australasia, where cat species have never been native and there were few equivalent native medium-sized mammalian predators. Native species such as the New Zealand Kakapo and the Australian Bettong, for example, tend to be more ecologically vulnerable and behaviorally "naive" to predation by feral cats. Feral cats have had a major impact on these native species and have played a leading role in the endangerment and extinction of many animals.
Impact on birds
The domestic cat is probably a significant predator of birds. Current UK assessments indicate that they may be accountable for an estimated 64.8 million bird deaths each year. Certain species appear more susceptible than others; for example, 30% of house sparrow mortality is linked to the domestic cat. In the recovery of ringed robins and dunnocks, it was also concluded that 31% of deaths were a result of cat predation. The presence of larger carnivores such as coyotes which prey on cats and other small predators reduces the effect of predation by cats and other small predators such as opossums and raccoons on bird numbers and variety. The proposal that cat populations will increase when the numbers of these top predators decline is called the mesopredator release hypothesis.