The best estimate of the number of pet cats in the UK is 8 million, according to the Pet Food Manufacturers Association, plus an unknown number of feral cats (those living wild).
There is a species of wild cat, found in Scotland, which is native to the UK, but domestic cats are not part of our native fauna. They are maintained by people and do not need to hunt to survive.
Cats are individuals: their behaviour varies widely. Some will be prolific hunters; some may catch nothing at all. Town cats live at higher densities than country cats. Although each town cat will catch fewer prey overall than a country cat, their prey will include a higher proportion of birds.
Most cats are opportunistic hunters they will catch whatever they come across rather than actively hunting a particular species. This means whatever is most abundant or vulnerable is most likely to be caught. Cats will catch prey even if they are not hungry.
According to a recent major survey by the Mammal Society, birds comprise a relatively small proportion (about 20%) of all the creatures caught by cats. Most of the rest of their catches will be mice or voles. Most of the birds are taken around dawn and dusk, during the breeding season and mid-winter.
It often seems that cats catch more birds than small mammals. This is because birds are mainly caught during the day, so you are more likely to see it, while mice and voles are mainly caught at night.