The ferocious killer dressed up as a pet

Let out to the lawn for her late-night pee, the dog is likely to rocket off into the dark like an Exocet, outpacing even her own hysterical yelpings. How, at that speed, she can negotiate the acre's tangled labyrinth is beyond imagining, and in pursuit of what, we can never be sure. It could be a fox or a hedgehog (nimbler in a sprint than you'd think), but chances are it's a cat, on patrol from the farm next door.

It's now 10 years since we lost the last of our supposedly "outdoor" cats that spent most of their time at the porch windowsills, lobbying for access to the kitchen or a bed. An allergy to cat dander brought a regretful decision not to renew the line, a deprivation eased by the hope that what we lost in feline company we might make up in a richer life with birds.

That expectation, at least, has worked out well. Around the house this morning, blackbirds and song-thrushes roved through the grass without a backward look; a party of goldfinches took a break from the nut-feeder to rummage for seeds on the paths; a wren ran about like a mouse on the open gravel, totally focused on its hunt for morsels of microscopic animals.

For the moment, and in daylight hours, at least, we seem to have given the birds back the freedom of the ground. But as the spring wears on, and they spend more time at low level to find food for their young, we will often see one or other of the burly cats of the townland prowling the acre in hope of prey.

It's remarkable, really, how we blandly exclude the domestic cat from the roster of carnivorous mammals. Nobody knows how many cats there are in Ireland, although the pet-food industry may think it has some idea. In Britain, it offers the awesome total of 7.5 million domestic cats, plus 800,000 living wild. Multiplied by average catches, as recorded in a recent Mammal Society study, this suggests the British house-cat population could be killing 300 million animals and birds every year.

Tony Whilde, the ecologist who lived beside Lough Corrib and wrote The Natural History of Connemara (1994), once kept track of the prey his two cats brought home to his back porch over a period of 41 months. Of almost 500 small mammals and birds, getting on for 200 were field mice and more than 90 were pygmy shrews - animals more at home in rough grassland and scrub than in suburbia. Among the birds, 32 robins and 19 chaffinches topped the list.

In the Mammal Society study, the kills-or-capture records of 964 cats spanned only five months but yielded an annual average figure of 40 victims per cat. Country cats killed substantially more than town cats, having, perhaps, greater opportunity and obtaining more of their own food. There were far more mice, voles and shrews than birds, and these were largely "bird-table" species, led by housesparrows, blue tits, blackbirds and starlings.

The figures for amphibians and reptiles are more surprising. In the extrapolated totals, Britain's cats may be killing an annual four million frogs, 180,000 toads, 170,000 newts, 370,000 lizards and 700,000 slow-worms. "Out of how many?" is the question to be asked when trying to weigh up real pressure on a species.

A total of 230,000 bats could be significant, since they are slow to reproduce. The same number of tiny, roof-dwelling pipistrelles would not matter as much as the inroads made on much scarcer or more vulnerable species already under threat from man-made causes.

Where particular bird species are in decline for other reasons, the fact that cats kill adult birds in winter could come to matter; most other predators take a toll of young birds or eggs. But one small comfort is that cats do not, in general, go in for the "surplus killing" common to such predators as foxes, mink or stoats. Once a cat is full, it stops killing, even if it continues to stalk and catch, and perhaps seem to play with its prey (the shrew, in particular, which has distasteful skin glands).

Does it help to tie a bell on a cat? Apparently not: 232 of the cats in the Mammal Society study were bell-wearers, yet they caught as many birds and rather more mammals than the cats without them. I wonder if the cats had been belled because they were such dedicated hunters in the first place?

SOME of the biggest killers in the study were the grizzled eight and nine-year-olds. And among the most convincing hunters of my own experience have been the ageing, feral tomcats of the Connacht countryside.

Once, on a gloomy day in early spring, I met one of these powerful creatures prowling through the garden, having earlier massacred a couple of our ducks. But what registered even more was its alien untouchability: nothing in those mean yellow eyes invited me to stretch out a hand.

Domestic cats are descended from the North African Felis sylvestris lybica, but did we ever have its wildcat cousin, Felis silvestris, native to Britain and Europe? Its bones have appeared in a Mesolithic campsite at Lough Boora in Co Offaly and again in Bronze Age sites at Newgrange and Tipperary, but its apparent and strange extinction after that is one of Ireland's mammalogical mysteries.

Killer cats will not, one hopes, figure too largely in the all-Ireland Nest Record Study just established by Gavin Fennessy at the zoology and animal ecology department of UCC. He has been making a special study of the nesting of robins for some years and now, with sponsorship from the Heritage Council, he is extending it ambitiously to common birds in general.

His website (www.nestireland.com), the first of its kind in these islands, encourages the public to monitor local nests and provides forms on screen to record such things as choice of nest site, time of building, clutch size, survival of chicks, and so on. For those who prefer paper, his study cards and leaflets are available from him at the Zoology and Animal Ecology Department, Lee Maltings, Prospect Row, University College, Cork.

viney@anu.ie