Cats and wildlife: The hunter of suburbia

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Ground-breaking new research is following domestic cats to find out what impact these predators are having on our wildlife. James Fair investigates.

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Domestic cats: the hunter of suburbia article spread

Ground-breaking new research is following domestic cats to find out what impact these predators are having on our wildlife. James Fair investigates. Photographs by Steve Orino

There is something about the feline form that is innately beautiful to the human eye, as cameraman Gordon Buchanan observed on the BBC’s recent Lost Land of the Tiger series while staring through his lens at the languid, liquid shape of a leopard cat. “Whether it’s a cat this size or a tiger, they’re just perfect,” he murmured.
 
It’s true. As my partner and I watched the programme, she turned to look at the equally gorgeous and highly evolved carnivore curled up on the sofa next to us, head hidden under a furry paw, butterscotch belly exposed as if waiting to be tickled.
 
“You’re a hunter, too,” Louise cooed with palpable satisfaction.
 
The reluctant predator
 
The extent to which Esme qualifies as a ‘hunter’ is a matter of sometimes bitter dispute in our household. She hasn’t brought in any prey items for the best part of two-and-a-half years, and all anecdotal evidence suggests that she spends the nights fast asleep on the sofa or on our bed.
 
Nevertheless, Louise likes to imagine Esme as a fierce and skilful predator, dispatching woodmice, voles and rabbits in the wilder corners of our country garden.
 
Even if this were true (and I don’t believe it is), she is a well-fed tabby who has the luxury of being able to hunt as a leisure pursuit, rather than because she really needs to. She is the feline equivalent of a big-game trophy hunter who wants a buffalo head for his Appalachian log cabin back home.
 
Killers in our midst?
 
I think Louise is fairly typical of how many British people view their pets. We love the idea of a killer in our midst, whatever the toll on our native wildlife.
 
That impact has been much discussed in conservation circles over the past decade, certainly since a report published by the Mammal Society in 2003 concluded that British cats had taken an estimated 92 million prey items over a five-month period.
 
When the researchers factored in kills that had not been ‘returned’ (brought back to the cat’s owner), it was extrapolated that the overall tally could be as high as 275 million individual animals every year. 
 
It is a figure that is widely accepted, and quoted by many organisations including the RSPB, the British Trust for Ornithology (BTO) and the Bat Conservation Trust.
 
Tiddles' diary
 
Now new research, due to be published in 2011, is taking a closer look at what our domestic cats are up to.
 
Rebecca Thomas, a PhD student in environmental biology at the University of Reading, persuaded 210 people in the town (and their 250 cats) to take part in a study in which they kept a ‘prey diary’ of exactly what Tibbles and co brought in over a two-year period.
 
One of the study’s aims was to generate data for every season and for more than one year, as opposed to just a few months, so that Rebecca could make a more accurate estimate of how many individual animals cats were killing.
 
 Clyde poses with one of his latest 'returns' - a woodmouse.
 
 
Revised figures
 
With the fieldwork complete, several things have become clear. By including prey returns over the winter months, when catches are reduced, the study has produced an average number of kills per cat that is lower than that normally quoted.
 
Rebecca found that each cat returned an average of 4.39 animals a year, which, if true for the UK’s estimated 10.3 million cats, would result in a kill total of 45.22 million mammals, birds and amphibians.
 
But you also have to factor in the kills that are not returned, something that is yet to be properly investigated. One study estimated a ‘return rate’ of 30 per cent, but that was based on data from only 11 cats.
 
Still, using this figure as a starting point, you arrive at a killing spree of 150 million animals. It’s a lot – but much less than 275 million.
 
A guessing game
 
Rebecca is uncomfortable with this sort of extrapolation, partly because we have no idea if the 30 per cent figure is accurate or not. “And you can’t really compare urban and suburban cats with rural ones,” she adds. “People will extrapolate and that’s fine, but I won’t.”
 
And the overall figure is relatively unimportant, as one of the authors of the original 2003 report, Robbie McDonald, points out.
 
“A cat population of millions, multiplied by any number of wild animals caught, will result in an impressively large headline tally, and whether this is 100 or 200 million is rather immaterial. The issue, in conservation terms, is calculating the impact, which is a notoriously difficult problem.”
 
Leaving that aside, what else has Rebecca discovered?
 
She was surprised by the sheer number of birds that some of her cats were catching, particularly during the cold winter of 2009/10. “One cat that lived beside a woodland brought in a blue tit every single day for a fortnight.”
 
Additional kills may have been occurring because birds visiting feeders provided easy pickings.
 
Even more shocking were the terrible trio that between them brought back a weasel, three miraculously intact woodpigeon eggs and a blue tit nest – complete with chicks.
 
Alpha males
 
Rebecca’s other findings are also intriguing. There wasn’t much difference between males and females in terms of hunting success, she says, but there was great variation between males. In other words, there were some true alpha males – and some utterly useless ones.
 
There are many more factors to consider, too. The sub-lethal ‘fear effect’, for example, may mean that anxiety of being predated will affect a species at a population level more than predation itself. If a robin is afraid of the local tabby stalking his patch, he will be less likely to visit the ground to feed, possibly affecting his fitness and breeding success.
 
On the other hand, it may be that cats are simply targeting the sick and injured, much as lions take out lame wildebeest in the Serengeti. And consider that our native fauna evolved to live alongside Felis silvestris, the wild ancestor of the domestic cat.
 
Reducing predation
 
Does any of this matter? No political party will ever legislate to curb cat ownership on the basis of their impact on rodents, birds and frogs.
 
And we already know some of the chief ways in which cat predation can be reduced – not allowing your cat out at night is one simple thing anyone can do.
 
The BTO’s Mike Toms says that there are probably other things, too. What if we were able to position our birdfeeders or manage our gardens in such a way that we reduced the threat that cats pose to wildlife? Would it be better, for example, to eliminate dense foliage where robins like to forage but which cats prefer for hunting?
 
“You can’t stop people from owning cats,” says Mike, “but you can improve the outlook for their prey.”
 
Sparrows on the menu
 
We might also think about whether we should help those species that are more vulnerable than others. House sparrows have suffered huge declines in recent decades, especially in cities.
 
As Rebecca says, “I’m not sure that cats are reducing population levels, but they may be adding to problems that already exist.” For a group of sparrows in an urban area, a high density of cats could be the final claw.