Cat survey reveals impact on birds

10 January 2013 by Tom Marshall

Some pet cats are killing a lot of birds around the UK, a new study shows. Most don't do much harm, but millions of marauding felines add up to what could be a serious problem for the nation's wildlife.

Domestic cat

The study's authors say owners could do more to stop their pets scoffing increasingly-threatened bird populations. Sadly they don't seem keen to do so; conservationists have more work to do engaging with pet lovers and persuading them to take action.

Scientists have long suspected cats are partly to blame for the decline of many British wild birds, but until now they've had little hard evidence. The animals' popularity as pets means they're kept at very high densities in many towns and cities - much higher than they'd reach in the wild. Birds living in these urban areas face a relentless threat.

Dr Rebecca Thomas wrote the recent paper in PLoS ONE based on the results of her doctoral research at the University of Reading. She surveyed cat owners around town to find out how many prey their pets brought home, as well as what they thought about this predatory activity and whether they were prepared to do anything about it.

One finding is that cats' hunting prowess varies greatly. Only 20 per cent brought back four or more dead animals a year; 22 per cent of owners had to manage with no prey gifts at all throughout the entire multi-year length of the study. It turns out that a relatively small minority of felines is responsible for most of the havoc. They bump the average up to an estimated 18·3 kills per cat per year. Previous studies suggest cats bring home around one in three things they kill, letting scientists estimate overall kill numbers from data on prey returns.

"The density of cats in urban environments is the biggest issue," Thomas says. "Even if a cat isn't killing often, there are so many of them in a small area that they can have a very serious impact. Owners might think their cats only catch two or three birds a year and that won't make any difference, but they need to understand all the other pressures that wildlife is under from habitat loss and environmental change."

As well as surveying the dead things cats brought back to their no-doubt grateful owners, the team investigated general awareness of cat-related conservation problems, as well as willingness to consider various possible countermeasures.

It turns out that people's understanding of the problem is variable, and willingness to consider steps to solve it is limited. 46 per cent of non-cat-owners think cats are a nuisance, compared to a surprisingly high 19 per cent of cat-owners. Owners in particular are often not aware of the conservation issues; 16 per cent reckon cats have no effect on local bird populations and another 51 per cent only a small effect.

Owners and non-owners alike were asked what they thought of various options that could reduce cat predation, ranging from banning cat-ownership in ecologically-sensitive areas, or even in all towns and cities, requiring all cats to wear a bell or other anti-predation device, keeping cats indoors during the day, registering them with the local council, sterilizing or even declawing them.

65 per cent of interviewees would consider mandatory bells for cats, and more than 60 per cent could be willing to countenance mandatory sterilization. More than half of those asked were also prepared to consider compulsory registration. But the other options were extremely unpopular, particularly with cat-owners; fewer than 16 per cent of individuals supported a daytime curfew.

Bells look like one of the few real options. There is some evidence that cats learn to compensate for the bells, so they can still sometimes hunt successfully. But recent studies suggest that bells are a serious hindrance and do reduce hunting effectiveness.

Controlling the problem will probably involve voluntary agreements and negotiation with cat-owners, Thomas says, since there's little political possibility of sweeping reforms from central government, such as nationwide compulsory cat-registration. Another smart and potentially palatable move would be to encourage cat owners to keep their cats inside at dawn and dusk, the times at which birds are most vulnerable. Thomas adds that as well as trying to keep cats under control, people can also help improve urban biodiversity directly by creating wildlife-friendly gardens and feeding birds.

'Spatio-Temporal Variation in Predation by Urban Domestic Cats (Felis catus) and the Acceptability of Possible Management Actions in the UK' - RL Thomas, MDE Fellowes, PJ Baker (2012). PLoS ONE 7(11): e49369. doi:10.1371/journal.pone.0049369