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Wild Animals Killed by Cats

The Mammal Society

To find out more about the killing habits of cats in Britain, The Mammal Society carried out a survey of almost a thousand cats during the spring and summer of 1997. The respondents were everyday cat owners recruited through a big media drive kicked off by BBC Wildlife magazine and followed up with a range of newspaper and magazine articles and radio interviews. Each completed a form with details of their cat including its name, colour, age, sex and the amount of food it was given. But the more important information was included on the reverse of the sheet – the list of what species the cat killed between 1st of April and 31st of August. This initial survey was followed up by a questionnaire to the respondents asking for more details about their cat, where it lived and its general environment. The questions included whether or not the owners fed birds and mammals in their garden, whether or not the cat was kept indoors at night and if it wore a bell. Dr Robbie MacDonald, of Bristol University, analysed the results.

During the survey period our sample killed over 14,000 mammals, birds, reptiles and amphibians. With the current pet cat population in Britain estimated as being in excess of 9 million, our domestic moggies could be killing 250 million creatures a year, or more than 37 prey items each, over that period. Cat lovers leap to the defence of their pets when they hear this and point out that our survey took place at the peak time for prey numbers, especially birds, that many cats live in urban areas and rarely go outside, and that some cats kill nothing at all. In fact sixty six of our responding cats killed nothing and we received more than one apologetic note along the lines of “Sorry, Sammy killed nothing for the survey“. Furthermore our survey did not include the 800,000 or so stray and feral cats nor the prey items of those cats too lazy or wily to carry them home. Moreover, by using other survey work on cat predation over an entire twelve month period, we were able to adjust our figures to reflect the predatory habits of cats over a year.

Cats are undoubtedly mammal specialists and true to the stereotype, mice are right at the top of the list. Our sample killed over 4,000 mice while voles were also high on the menu with almost 2,000 field and bank voles dying too. Cats killed almost as many shrews but most cats seem to be useless at ratting, probably because rats will fight back, and only 162 rats were killed during the survey, a figure which, even when extrapolated, does not begin to dent the brown rat population. The most worrying kill rates were those of scarcer mammals. Less common species, such as water shrews, harvest mice and yellow necked mice, along with protected dormice (12) and water voles (20) also figure in the killing lists. These numbers suggest that domestic cats could be a significant pressure on all of these mammals and may be one of the major predators of dormice.

Cats also took larger mammals including high numbers of rabbits as well as occasional squirrels, weasels and even a few stoats! Two hamsters were killed, hopefully by the cat of their owner! Cats took a worrying number of bats, generally by waiting outside a roost entrance and hooking the tiny animals as they emerged at dusk.

When it came to birds, sparrows were the top prey item by a very long way and all of the more common garden birds featured high on the list, forming the vast majority of the birds killed. Nevertheless, the sheer variety of species was astonishing and included jays, woodpeckers, gulls, treecreepers, goldcrests, swifts and swallows. One cat made a specialism of the last species, hiding beside a pond and grabbing the birds as they swooped down to drink. As for the reptiles and amphibians, frogs were well to the fore, followed by slow-worms. Thereafter the numbers of other species were quite low and, although neither adders nor smooth snakes featured on the list, rare sand lizards certainly did.

Our survey also told us a great deal about Britain’s cat population and our sample was clearly a suburban set belonging to responsible owners, for 98% were neutered and a third wore bells! The amount of food given to a cat made no detectable difference to its kill rate and simply seemed to make it fitter to carry out more recreational killing. Fat cats, however, did tend to kill less. Males, or one time males, killed slightly more than females and older cats certainly killed much less than young ones. Once past the age of two, the kill rates of most cats, except for a few grizzled old experts, dropped dramatically.

Bell wearing cats seem to kill fewer mammals although bells apparently offer little protection to birds. The modern generation of sonic collars appear to be the answer here. A survey carried out by the British Trust for Ornithology showed that CatAlert, a sonic collar which emits a regular signal, made a significant difference to cat predation on birds. Indeed their figures indicate that the numbers of birds killed by cats wearing one of these devices, fell by 65%. The Mammal Society survey also demonstrated that cats, whose owners feed the birds in their gardens, killed fewer birds. It is suggested that this somewhat strange result could be explained by the fact that the many watchful eyes of birds attracted to food in one place, will spot hunting cats more readily and sound the alarm accordingly.

Cats living in flats appeared to kill fewer victims than those in houses. This may simply be the fact that they cannot be bothered to carry their kills up all those stairs. The more likely explanation, however, is that these cats live a more urban existence and spend much or all of their time indoors. Certainly keeping cats in at night would seem to have several advantages, not least the fact that the cat itself is less likely to be run over. Our survey showed that cats confined at night killed fewer mammals although this did not seem to affect their bird kill rate in any appreciable way. A local experiment using two of the bigger killers from the survey has shown that their kill rate fell by a remarkable 80% when they were kept in at night. In fact it seemed to deprive them of the desire to hunt and significantly reduced their daytime killing too.

Research in Australia has shown that suburban cats have comparatively small daytime ranges of only 3.75 ha. based around their home. At night, however, their range can be as large as 28 ha and up to 0.9 kms away in open countryside. Those owners, convinced that their nocturnal prowling feline’s early morning mouse present is a sign that their cat is suppressing the local rodent population, may be looking at the corpse of an animal killed more than half a kilometre away.

While The Mammal Society is far from being anti cat, it has to be recognised that cats are the only pets allowed to roam free. There are 38 times more cats than the estimated pre-breeding population of foxes and 6 times more than all the wild terrestrial predators combined. Uncontrolled by their food supply and kept fighting fit by their owners, it is hard to see how cats cannot be exerting a pressure on our native fauna. Just as mink have devastated the water vole population, already under significant pressure from habitat loss, so cats could be the final push for an as yet unidentified species led to the brink by some totally unrelated factor.

What You Can Do as a Responsible Cat Owner

Apart from living in a flat and keeping only old and obese cats, how can you reduce the number of wild animals killed by your cat?

  1. Fit a collar with a bell, but choose a noisy one rather than some of the tiny ones which rattle rather than jingle.
  2. Fit one of the new sonic collars, CatAlert, made by Willana Lifesciences, has been shown to be effective by the BTO.
  3. Feed the birds in your garden preferably on a well constructed bird table supported on a single pole and made as cat proof as possible. Be sure to site it well away from cover and branches or roofs from which a keen cat could make a surprise attack.
  4. Provide your cat with toys and show it affection rather than ignoring it: both are said to be ways of reducing its boredom and thus its recreational killing.
  5. Keep your cat in at night by locking its cat flap and providing a litter tray, or, even better, consider keeping it in a well built and interesting run during the day.
  6. Look up the websites of the American Bird Conservancy’s Cats Indoors Campaign and the Canadian ‘Cats in Kennels Program’ Cats in Kennels Campaign. You may pick up some interesting ideas.

The Mammal Society – the voice for British mammals, and the only organisation solely dedicated to the study and conservation of British mammals.

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