As the numbers of abandoned cats in towns and cities increase, complaints of property damage, unpleasant odours and noise tend to rise. Cats reproduce quickly and are able to survive without the aid of an owner. This resilience lends itself to increasing competition for food and territory and to the transmission of disease among other stray cats.
In UK there are at least 1.2 million domestic cats living out a feral life.
In the USA, in 2009 there is a estimated 82-88 million pet cats of which 80-85% are sterilized. In addition, 10-90 million free-roaming (community) cats, of which around 2% are sterilized. Feeding unowned community cats is a common activity: between 8% and 26% of households in five States feed unowned cats and about 50% of community cat feeders do not own cats.
In Australia, feral cats in national parks live predominantly on rabbits. In dry years, when rabbits are scarce, cats are forced to concentrate on native animals or die of starvation. Such small native fauna includes dunnarts, lizards, snakes, grasshoppers and spiders. The average weight of feral cats was under 4 kg, no exceeding 6 kg, which is about the same as an average house cat.