DOMESTIC CATS - WILDLIFE ENEMY NUMBER ONE OR CONVENIENT SCAPEGOATS?
In January 2001, it was claimed that domestic cats kill about 275 million other animals in Britain each year. The victims include declining species such as water voles, dormice and house sparrows. Alarmist reports with an anti-cat bias appeared in The Times, Sun and Guardian newspapers and on Monday Feb 5th, renowned wildlife photographer Chris Packham was interviewed on BBC Radio 4 and asserted that cats should be shot. In fact the survey figures are open to interpretation and should be put in perspective against the number of small mammals killed by humans and by habitat destruction.
These flawed statistics have already been used to fuel a debate against cats, with people advocating shooting them. Even before the survey RSPB members regularly wrote to magazines and radio news programs (often using the most tenuous link to other topics) to condemn cats and BFSS (the bloodsports supporters' body) were attempting to claim that bloodsports are 'more humane' than cats. The flawed conclusions from this latest survey are calculated to add fuel to the fire.
In fact the data presented by the survey is extremely poor, coming as it does from such a small sample of the feline population, over such a short timescale. It did not take into account the percentage of the cat population which has no access to prey and hence it would be more accurate to call it propaganda, not statistics. Some of the conclusions drawn fail to take into account important facts about the ages, locations and territories of the surveyed cats. Such a small-scale survey cannot be representative of an entire feline population. Either the survey results have been over-simplified to produce alarmist but statistically unsound extrapolations (in actual fact propaganda) or the survey itself is seriously flawed in concept.
UNREPRESENTATIVE SAMPLE AND TIMESCALE
The Mammal Society, which published "Look What the Cat Brought In" argued that cats pose a serious problem for wildlife but admit that they have no idea whether the cats studied are representative of cats in general. Human activities have been, and still are, a far more serious threat to our wildlife. However, by spotlighting the domestic cat we humans can conveniently ignore, or are even encouraged to ignore, our own often devastating effects on wildlife and wildlife habitats. Michael Woods of The Mammal Society summarised the results of the survey which ran for the 5 months up to August 31 1997. The survey looked at the kinds and numbers of animals killed by domestic cats but the small sample size and short timescale makes his extrapolated data of dubious value.
The Mammal Society looked at the kill or capture records of 964 cats, amounting to more than 14,000 prey items. The mean number of catches or kills per cat over the five month period was 16.7 which gives an annual average per cat of 40 victims. Assuming that this tiny sample was representative of the general feline population of Britain the figures were scaled up. Multiplying the pet industry's estimate of 7.5 million domestic cats by 40 suggested that the British cat population could be killing at least 300 million animals and birds every year. The survey notes that this does not include the animals that cats killed and ate away from home nor the kills of the 800,000 feral cats believed to be living in Great Britain and suggests that the figures are therefore an underestimate.
In fact the converse - an overestimate - may very well be true. Of Britain's 7.5 million pet cats, some 10% (a figure which is increasing) live indoors and have no access to prey. A similar percentage of cats are in the care of animal shelters at any one time - these have no access to prey. Kittens, elderly cats and cats with certain physical disabilities are ineffective hunters; while I have no actual figures of how may cats are too young, too old or too disabled to hunt or how many do not have a predatory disposition, 10% is as good a guess as any. In addition, how many of the alleged 'kills' were already dead and were scavenged by an opportunist cat? Did the Mammal Society ascertain the cause of death of any of the kills?
As many as 30% of our 7.5 million cats do not hunt. The total number of prey animal kills should be reduced by 30% and even this could be an over-estimate.
SMALL SAMPLE SIZE = INACCURATE RESULTS
To demonstrate the uselessness of extrapolating annual figures for 7.5 million cats from a survey of 964 cats over 5 months, I'd like to present some equally dubious statistics. A certain cat shelter near me has approximately 100 cats in care at any one time. Over a 5 month period, the cats in care account for nil prey items. Scaling this up for a feline population of 7.5 million means that cats in general kill nil prey or what about results extrapolated from a sample of 15 free-roaming domestic cats surveyed over several years? Of the 15 cats observed, only 2 hunted successfully. The first averaged 1 prey animal per year, discounting invertebrates such as slugs. The second averaged 2 prey animals per year. Their averages were closer to 30 prey animals in a lifetime, not 30 per year. The remaining 13 cats did not hunt although one scavenged winter-killed birds from the garden on two or three occasions. 6 of those cats showed an interest in wildlife from an indoor windowsill even though they had the option of going outdoors at will. My garden attracts birds, frogs and house-mice and a nearby wood harbours squirrels, wood-mice and a wider variety of birds.
Obviously these results are ludicrous because I know that the samples are unrepresentative, but it does illustrate how dubious statistics can be obtained from a small sample. A small sample can be carefully selected to give you just about any results you want in order to prove whatever conclusion you want them to prove. A sample of less than 1000 cats is not much better as there is still scope for selecting unrepresentative cats.
The survey hasn't been adjusted for the percentage cats which are confined, those which scavenge already-dead mammals and birds and those which do not hunt due to their age, temperament or physical condition.
TOWN CAT, COUNTRY CAT
Many of Britain's urban ferals, live on handouts from humans and scavenging from refuse although some also prey on rats and mice attracted to the same refuse. Cats - pet and feral - in urban areas have far less access to wildlife - our towns and cities are pretty inhospitable to most species except for those which can live on our refuse and the vermin attracted to that refuse. They may prey on those garden birds which manage to live in gardens.
In rural areas, cats have a far wider range of prey although this is dependent on the local geography. This sort of prey is also attracted into gardens by food placed there by well-intentioned householders. The householders, in effect, lure the prey within easy reach of a cat which would not otherwise hunt. The cat's instincts tell it not to miss an easy meal! It's worth noting that this supplementary feeding can keep some prey populations at artificially high levels hence the higher numbers of those species in the kill tally.
It is ironic that in the past, cats were valued for their predatory abilities. In fact it was these very predatory skills which led to feline domestication in granaries in parts of Egypt and independently in what is now Pakistan. A cat's worth was once calculated in relation to their proven ability to catch mice. In rural areas they are still highly valued as ratters and rabbiters. Cat shelters in more rural locations still receive requests for cats with proven hunting skills or for working cats (including ferals/semi-ferals).
It is generally felt that there are more cats living in urban and suburban areas than rural ones so The Mammal Society used the presence of nearby arable fields to indicate whether the cat in question lived in a rural habitat. Using that criterion, 39% of the cats surveyed lived close to arable land ("country cats") while 61% were "town cats". During the 5 month survey the country cats killed 18 items on average but the town cats managed only 12.5 items.
Has the survey chosen cats with an already proven track record in catching prey? Not one of my own cats managed 12.5 items in a period spanning several years despite ample access to prey! Carefully selected survey subjects are sometimes deliberately selected to produce alarmist statistics (as happens in Australian surveys produced by anti-cat factions) or was the selection of good hunts accidental because the Mammal Society was simply unaware of the mix of hunting skills or of the percentage of cats with no access to live prey?
I have worked in a rurally located cat shelter close to fallow fields and stables (whose feed bins attract a large number of rats); at one point we had 10-12 neutered ferals roaming free around the shelter. Two thirds of this population relied on human handouts at regular feeding stations. Only one third actively hunted. Three of the hunting cats were littermates - some cats are genetically more predisposed to hunting than others - and caught mice, rats, frogs and pigeons. Since I cleaned out their sleeping quarters, I got a clear picture of what these cats were killing each evening from the debris.
Kill rates generally decline as cats get older and slower and their senses less acute. The Mammal Society survey noted that 2 year old cats killed most, although some of the most successful hunters were the grizzled and really experienced 8 and 9 year olds who had well-honed hunting strategies and probably established territories which they defended against other cats. Once again, it was not stated whether location and prey abundance contributed to the kill record. The lack of an age breakdown for the cats surveyed means that the age-related kill-rate cannot be put in perspective i.e. were all 8 and 9 year old cats more successful than the other cats or were there only one or two 'specialists'?
Michael Woods, the Mammal Society’s co-chairman, claimed that "The potential effect of cats gives considerable cause for concern, especially as cats will not bring home all the animals they kill, so this study is probably an underestimate. Cats can roam more than half a mile away each night and have a home range of up to 28 hectares. "Many owners think that when their cat brings home a mouse it is suppressing the local rodent population but this is clearly not the case. Cats are killing animals on a much wider scale."
How many cats actually roam over these distances? Once again, the results are presented in such a way as to suggest that all cats behave in the same way. My own cats, for example, have a home range limited to my front and back gardens and do not roam at night. Far from being an underestimate of all prey killed, the assumption that the small sample is representative of the entire cat population leads to an over-estimate.
ARE COLLAR BELLS EFFECTIVE?
The bell-wearing status of 740 of the surveyed cats was recorded. 232 (31%) of those cats wore bells and 508 (69%) didn't. However, those wearing bells killed an average of 19 small mammals while those not wearing bells only averaged 15. The raw data would lead to the conclusion that belled cats are better hunters, killing a similar number of birds to non-belled cats but killing 33% more mammals. Are they better hunters because they have to be more stealthy in order to keep their bells quiet? Anyone who has watched a stalking cat will realise that its economy of movement does not cause a bell to jingle. By the time it pounces - and the bell jingles - it is already to late for the prey.
The figures are misleading. They have not been broken out by the age or temperament of the bell-wearers or the hunting skill of the normally belled cats when not wearing bells and vice versa. There are simply far to many variables for any accurate conclusions to be drawn from the sample.
Cats which are less prone to roaming (home-bodies) are less likely to wear ID collars. Most ID collars have bells attached by the manufacturer and it can be quite an effort to detach the bells. The majority of owners use collars as a means of identity; relatively few use them as a means of reducing kill-rates. Cats which go out more and range further are more likely to wear ID collars; they are also the cats most likely to hunt.
Some owners bell their cats in the hope of reducing the number of kills. They are belling already proven, stealthy hunters. The survey did not provide figures for the number of prey killed by a good hunter when it wears a bell compared to when it does not wear a bell. I would consider the figures on bells to be invalid as the belled cats may be catching more prey simple because they are better hunters.
The other reason that non-belled cats appear less successful hunters is most likely due to them being less inclined to hunt and staying closer to home (including more time spent indoors).
THE TOLL ON RABBITS, RATS, MICE AND OTHER SMALL MAMMALS
Not surprisingly, mice were the most popular prey , with the sample killing 4196. Most of us live in close proximity with house mice or field mice without realising this; therefore the prey is close at hand. It is also because mice are more nocturnal than the other species and cats are most active at dusk and dawn. In fact the mouse is one of the reasons we started keeping cats in the first place! Voles were the next highest, with almost 1949 field and bank voles reported. 946 shrews were killed.
Only 162 rat kills were reported; rats fight back and rat-killing is a specialised skill. There are cats who specialise in ratting, but these might have figured in the survey. The rat toll in the survey suggests that they are poor ratters, killing just over 3 million rats a year; however some factory cats and stables cats dispatch as many as 4 or 5 rats every night. With 326 million rats born every year, the rat population is not in imminent danger. Rats are routinely poisoned and cats will tackle dying rats (often fatally ingesting the poison themselves); once again there is the possibility that some of the rats "killed" were actually retrieved in a dead or dying state.
Less common species which featured in the survey were water shrews, harvest mice, yellow-necked mice and protected species such as water voles (20) and dormice (12). The scaled up figures from the survey suggest a serious impact on harvest mice with an estimated 1.5 million harvest mice a year, taking into account their limited distribution and reproduction rate (11 million harvest mice are born annually). However the harvest mouse habitat is squeezed by modern agricultural methods and their decline has more to do with humans than with cats. An unknown number of harvest mice are slaughtered by modern harvesting methods.
The figures suggest that about 15 million rabbits are killed annually, though it did not say whether the rabbit distribution had been taken into account. It represents a small percentage of rabbits which breed extremely quickly. Once again, there are cats which specialise in rabbiting (killing one or more rabbits or, more often, rabbit young per night), though these might not have appeared in the survey.
The relatively low number of rabbits killed compared to the high number of mice and voles has a surprisingly simple answer. A single rabbit provides a more substantial meal. A cat consumes a certain weight of prey per day. It requires more mice or voles to make up this weight than it requires rabbits. Hares were not represented on the published results, though cats will take unattended leverets. Hunting, beagling and hare-coursing exact a more serious toll on adult hares.
In general, cats tackle creatures smaller than themselves. Though there are exceptions, none were reported in the published figures. Surprisingly enough, cats have sometimes come into conflict with foxes, usually while scavenging, and have occasionally killed or fatally wounded the fox.
Cats were found to be killing some larger mammals, including squirrels, weasels, stoats and two hamsters (these presenting a very easy target for intelligent cats who learn how to break into a hamster cage). There were also "a worrying number of bats" (30 bat kills were reported). The Mammal Society considered the bat records very serious as bats are slow to reproduce. They suggest that British cats could be killing 230,000 bats a year, but this is improbable considering the scaling-up of a statistically poor sample size.
REPTILES, AMPHIBIANS AND FISH
If the cats in the Mammal Society survey are anything like average killers (which they are not) then the figures for amphibians and reptiles (herpetofauna) are alarming. Every year, cats might be getting through 4 million frogs, 180,000 toads, 170,000 newts, 370,000 lizards, 700,000 slow-worms and 80,000 grass-snakes. It is claimed that they are putting pressure on reptiles which find gardens a haven away from inhospitable agricultural land. As we've seen, the Mammal Society's figures come from a sample so small in relation to the general feline population and over such a short timescale that the data produced is statistically poor.
Though some small cat species specialise in fishing (and the Scottish Wildcat is known to fish), the domestic cat is not generally an enthusiastic fish-catcher. Cats will tackle fish in shallower water or those confined to ponds. Goldfish are often confined in garden ponds which are often too shallow or too small or otherwise poorly oxygenated that the fish spend time at the surface gulping air and presenting very easy targets. They are also bright and move about, generally providing irresistable targets for any cat inclined to hunt (for non-hunting cats they are merely fun to watch).
The cats in the survey who managed to catch 31 goldfish might be helping with the conservation of frogs as goldfish eat tadpoles and frogspawn. The depleted number of goldfish in a garden pond might not be due to the cat though, herons have also learnt to exploit this conveniently captive source of food. The number of invertebrates killed by cats was not recorded, though cats will kill, retrieve or eat slugs, worms and insects.
Bird catching is made much easier for cats whose owners habitually feed garden birds at ground level, especially where garden shrubs provide cover for cats. Cats who would not normally hunt, or who are generally unsuccessful hunters, are presented with a veritable smorgasbord of unwary avian prey. The survey did not provide a comparison of bird kills according to whether or not the cat(s) owner fed the birds, thus attracting them into close proximity to the cat.
3,383 birds were taken by 964 cats in the survey. It was not stated how many of these were adults, juveniles or nestlings (since the latter may have been ousted from the nest before being taken by the cat). Many cats will also retrieve dead birds, but this fact was not given in the published survey results and there appeared to be no attempt to distinguish between retrieved birds and killed birds. My own cats have retrieved already dead birds, including birds which had flown into house windows and been killed or stunned or birds which had been struck by cars.
Of the supposed bird-kills, 961 were reported as "house sparrows" but could have been any of a number of small brown birds while 503 were recorded as unidentified species. More than 30 individuals each from 13 bird species were accounted for in the survey: 961 house sparrows/small brown birds, 344 blue tits, 316 blackbirds, 228 starlings, 145 mistle/song thrushes, 142 robins, 114 pigeons, 105 wrens, 82 greenfinches, 70 chaffinches, 52 great tits, 34 dunnocks and 33 collared doves. These species were apparently killed no because they are common, but because they turn up in gardens; once again the feeding of birds by the homeowner is probably a contributory factor.
A number of the species reported seem to be chance kills - such as yellow wagtails, bullfinches, nut-hatches, tree-creepers, goldcrests, swifts, swallows, red grouse, green and great spotted woodpeckers, jays, gulls and even budgerigars. The survey suggests that a sample of double the size would have found another dozen species taken in ones and twos. Some bird species, such as the reported 22 swallows, were taken by a very few cats which appeared to have developed specialised strategies such as hooking these birds off a pond as they swooped low over water.
The survey concedes that the 14 pheasants and probably the red grouse, were injured birds from shoots, so why does it not concede that many of the other 'kills' (and this applies to both birds and mammals) were retrieved in a dead or dying state e.g. from roadsides? I would assume that the gull was already injured, perhaps by a car, since gulls have vicious beaks and are well able to defend themselves. Few cats will tackle healthy adult gulls. Species not numbered in the results, but which I have known cats to prey on, include magpies, crows and jackdaws.
The thrush population is in general decline because of agricultural practices and in gardens its favoured foods - slugs and snails - are routinely poisoned with slug pellets and powder.
The survey claims that cats could be adding to the pressure being put on thrushes and other birds, however the impact from human practices is probably far greater as we continue to eliminate its food supply and nest sites.
HUMANS - AN EVEN WORSE DANGER TO WILDLIFE POPULATIONS
Although it is unlikely that cats alone will cause any species to become endangered in Britain, for those which are already under pressure for other reasons, such as thrushes, harvest mice, grass snakes and slow worms, the Mammal Society believes that cat predation could become significant. Population crashes are sudden rather than gradual and here cats could make all the difference. However are they merely deflecting attention away from the even more devastating effects of humans?
The greatest pressure on many of these creatures are human activities. Changed agricultural methods have displaced the harvest mice from our crop fields. The removal of hedges to create large combine-harvester-friendly fields is a major habitat loss. The move towards monocultures on farmland have made these places into veritable deserts which do not support the food sources needed to sustain healthy populations of small mammals or of songbirds.
According to Felicity Lawrence's work "Not on the Label", since the 1950, Britain has lost around 60% of ancient woodland, 97% of meadow (habitats rich in flora and fauna), 200,000 miles of hedges and 50% of birds that depended on traditional (non-intensive) agricultural fields. Instead of a wide variety of fruit trees with different seasons (supporting insects) only a few varieties are grown in order to provide uniform produce for supermarkets. Modern crop fields are huge monocultures (often growing alien crops such as sunflowers and oil seed rape) treated with fungicides, insecticides and fertilizers. Small mixed farms have gone and vast tracts of land are, from a wildlife viewpoint, sterile deserts. Many orchards have been grubbed up because supermarkets have forced the prices down so far that fruit growing has become uneconomical. The now-vanished hedgerows and field margins of long grass once supported small mammals and great numbers of insects. The only verges and hedgerows left are those bordering roads where millions of creatures are killed each year by traffic. This is what is really killing Britain's birds and small mammals. In trying to produce ever greater amounts of food ever more cheaply we have turned our once wildlife-rich country into habitat hostile to wildlife. However, since it is hard for wildlife lovers to change modern farming methods and markets or supermarkets demanding cheap, uniform produce, so they attack easier targets instead. Unless they are prepared to address the root causes of wildlife loss they cannot halt or reverse the loss.
Even our gardening methods - especially the physical and chemical war on weeds - are to blame. The building of housing estates, construction of bypasses through sites which support diverse wildlife, the pollution of rivers with farm slurry or industrial chemicals, the widening of existing roads and grubbing up of roadside hedges and filling in of ditches to improve driver visibility - these have a far greater impact on wildlife than do cats. The population of small mammals, birds, reptiles and amphibians has lived alongside cats and native carnivores (and birds of prey) for centuries.
Humans are also responsible for introducing the mink, a voracious predator, into Britain. Mink are efficient hunters and pose a threat to small mammals and to birds which nest on river banks. Human activities have upset this balance, but rather than modify our own activities, we use dubious statistics to find and blame a scapegoat.
We have ripped up or built over natural habitats, we have filled in ponds, dammed rivers, caused pollution of land, water and air; our livestock farming and arable farming methods have become more intensive and changed the landscape; even our gardening methods have changed. Rather than modify our own activities, we find it easier to select a scapegoat so that we can continue to destroy natural habitats unabated.
AN ANTI-CAT MOVEMENT IN BRITAIN?
The "Look What the Brought In" survey results, though flawed, provide fuel for those who already have reason to dislike cats. I have read letters in the RSPB magazine calling for cat controls. The same people have written to national newspapers recommending that cats be confined, shot, declawed, defanged and goodness knows what. The lack of balance in the results, especially the failure to take a number of important factors into consideration, appears calculated to whip up anti-feline feeling in Britain.
The scaled up figures are alarmist and unrepresentative yet they are taken at face value by those who have little understanding of cat behaviour or of cat-keeping practices in Britain (e.g. the growing trend towards indoors-only). On Monday 5th Feb, wildlife photographer Chris Packham announced on BBC Radio 4 that domestic cats ought to be shot. In fact gamekeepers do shoot domestic cats, perceiving them to be a threat to gamebirds bred for sports shooting.
Back in the mid 1990s I had the dubious honour of speaking to a gamekeeper who shot cat. He found that those cats which wore a collar, especially a reflective collar make easy targets for gamekeepers. It would appear that the cat is fair game for a gamekeeper's gun for sitting on the wrong side of a boundary fence (or on the boundary fence, according to this particular gamekeeper), even if not engaged in any predatory activity or is retreating. The gamekeeper I spoke with had a quota system and had to provide evidence of meeting it. He found it all too easy to shoot a collared cat (a drawback of this type of identification), the probably much-loved pet of someone living on neighbouring land, and to remove the collar so it could be presented as a feral cat on his quota.
He wasn't particularly fussy about the cat being on his side of the boundary. He could simply claim that the shot and injured cat had crawled away. Where a post mortem shows the cat to have been killed outright and it was not on the gamekeeper's side of the boundary, the gamekeeper could be sued for damage to property (a cat is considered property) and potentially for a firearms offence. Should he lose his shotgun, and consequently his job, it would bring home the fact that they cannot shoot people's pets willy-nilly in order to meet some quota of predators killed. Microchipping could help to prove the ownership of an illegally shot cat.
If I appear to have little sympathy for gamekeepers it is because of their impact on wildlife in the name of protecting gamebirds which are intensively farmed for the shoot. This is a sport rather than a food source and large numbers of carcases are buried in pits. The intensively reared birds potentially compete with native species whose populations are already in decline. The intensively reared birds also carry bacterial infections, such infections might be spread to other creatures. Anything which might compete with the gamebirds is considered fair prey - even protected species.
A number of gamekeepers have been convicted for shooting or poisoning protected species of mammal or bird (e.g. kite), so their credibility is in doubt anyway. In Scotland, gamekeepers caused the near extinction of the Scottish Wild Cat whose population only recovered when the shooters were drafted into the army during wartime. The Scottish Wildcat is now protected, but this will not save it from the gun of a gamekeeper to whom it is just another ruddy cat.
The figures obtained from the survey have been scaled up with no regard for the percentages of cats which do and don't hunt. Even among ferals, some are fully reliant on humans to provide food. The sample size is miniscule and unrepresentative, the timescale too short and the conclusions statistically unsound.
Compared to human activities, the numbers pale into insignificance and the cat is serving primarily as a scapegoat. The prime causes of mammal and bird decline are habitat loss (building, farming methods), pollution (including pollution of rivers by slurry from farms), pesticide/chemical use and various other human activities including individuals who shoot wildlife. Probably the most successful 'predator' in the British Isles is the car - as well as the roadkill on or beside or highways, many animals die of their injuries. The most common roadkilled mammals appear to be foxes, badgers, hedgehogs, rabbits and squirrels, though smaller mammals and also reptiles are not uncommon (though are harder to identify in their squashed form). Where there are trees and hedges close to the road, a high number of birds are also killed as they fly from cover straight into passing vehicles.
The Mammal Society plan to extend their survey to address this problem and make the results available. Perhaps next time they will adjust the figures to take into account the percentage of the feline population which do not hunt and perhaps they will properly analyse the figures, rather than making sweeping generalisations based on a uselessly small sample.