Fatal felines: killer cats on the prowl

DORCHA, our normally docile cat, killed two baby wrens this week.

Summer brings out the worst in cats. Baby birds are leaving the nests. Just about able to fly and clumsy on their feet, they stand little chance against lethal predators in trim suburban gardens where there are few places to hide.

The anti-cat lobby says that pussies do untold damage to wildlife. Songbird populations are declining and cats, it’s claimed, are to blame for much of this. The purring pets have caused the extinction of 33 bird species worldwide. Cat defenders consider this charge unfair; the problems arose mainly on remote islands in the Indian and Pacific Oceans when cats were introduced by us.

The local birds had never seen mammals and were unable to cope with the predators. Cats, their supporters point out, were domesticated in the Fertile Crescent up to 7,000 years ago and have lived with people ever since. Yet birds such as house sparrows, wrens and tits are still around. So who is right? Assessing the damage cats do is exceedingly difficult. The problem has been studied in the United States, although we must be careful when comparing findings there to the situation on this side of the Atlantic. Stephen Vantassel of the University of Nebraska has identified four cat-keeping regimes, which he describes as ‘indoor’, ‘limited range’, ‘free-range’ and ‘feral’.

’Indoor’ cats are never let out of the house so they can’t kill birds. According to the American Bird Conservancy, this segment accounts for 35% of the cat population. This seems to be an unusually large percentage. It’s unlikely, certainly, that a third of Irish cats are permanently confined to barracks. Pet keeping regimes in America must be rather different from ours.

’Limited-range’ cats are allowed outside but must remain within their owners’ and immediate neighbours’ properties . These kill some birds, but it’s possible to track their movements and many of their victims come to light.

’Free-range’ animals, while fed and cared for by their owners, are allowed to go where they please. Their movements are very difficult to monitor, so nobody has any idea how many birds they kill. Cat enthusiasts claim that well-fed animals don’t bother to hunt but this, apparently, is not the case. Nor does spaying or neutering eliminate the instinct to kill. A cat, which was tracked experimentally, clocked up 1,600 ‘kills’ in 18 months. Its victims were mostly small mammals.

Finally, there are ‘feral cats’, ones which have left home and reverted to the wild state or are the offspring of such outcasts. Vantassel claims that a feral cat’s life expectancy is three to five years, a third that of a pampered house cat. The average ‘home range’ of a feral cat is 3km2.

A female can, in theory, produce up to five litters per year, although three is more usual. Up to four kittens are raised each time, so feral cat populations are self-sustaining. Born without sliver spoons in the their mouths, and with no food handouts or veterinary care, they depend for their survival on the rodents and birds they catch. Their behaviour is secretive and almost impossible to observe, so the number of their bird victims is anybody’s guess.

Vantassel thinks that there are at least 60 million feral cats in the United States, out of a total cat population of around 150m. He estimates a feral animal kills, on average, eight birds per year. However, he doesn’t say how he arrived at this; it seems to have been plucked from the air. A cat living wild would surely kill more than that. This means that American feral cats account for 480m bird deaths annually. When the victims of the ‘limited range’ and ‘free-range’ cohorts are added in, the total cat kill must be considerably higher.

The Royal Society for the Protection of Birds estimates that there are around 9m cats in Britain and that they kill about 55m birds annually. If we have the same ratio of cats to people as Britain, there are in the region of 800,000 cats in Ireland and they kill about 5m birds. It’s an unreliable figure but the best available.