There  is no real likelihood of cats wiping out entire populations of rodents, especially where there are high densities, and food for the rodents is abundant. However, cats can certainly help to keep the numbers of rodents in check, and this can be achieved even when the cats are receiving food from humans. The effectiveness of cats at controlling rats is most obvious when the rodents are breeding, because cats generally target the young rather than adults rats, which are more wary. At certain points in the year, however, cats may switch to hunting young rabbits or birds that can be caught more easily at that time, allowing the rodents population to swell once more