Despite the large numbers of birds killed by cats in gardens, there is no clear scientific evidence that such mortality is causing bird populations to decline. This may be surprising, but many millions of birds die naturally every year, mainly through starvation, disease or other forms of predation. There is evidence that cats tend to take weak or sickly birds.

We also know that of the millions of baby birds hatched each year, most will die before they reach breeding age. This is also quite natural, and each pair needs only to rear two young that survive to breeding age to replace themselves and maintain the population.

It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season, so cats are unlikely to have a major impact on populations. If their predation was additional to these other causes of mortality, this might have a serious impact on bird populations.

Those bird species which have undergone the most serious population declines in the UK (such as skylarks, tree sparrows and corn buntings) rarely encounter cats, so cats cannot be causing their declines. Research shows that these declines are usually caused by habitat change or loss, particularly on farmland.