Birds May 2020

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The Birds in Your Garden

Cats!  A “Marmite” topic if ever there was one.

Tabby cat Love them or hate them, they are undoubtedly garden birds’ number one predator, but what is their true effect, are they really responsible for the ongoing decline in bird numbers?

It’s difficult to get a handle on the true situation, but according to both the RSPB and the Mammal Society there is no scientific evidence that cats are responsible for the general decline in many garden bird numbers. Looking through academic (and quasi-academic) papers, the most salient fact is that the majority of trials run are local and lacking in rigour.

Domestic cats are rarely underfed, but most still hunt. There are also many feral and semi-feral cats around – but how many? Most trials count prey brought back to the cats’ home territories, but what percentage is that of what they catch?

TMarmalade cathe most recent figures of how much wildlife is killed by cats are from the Mammal Society. They estimate that cats in the UK catch up to 275 million prey items a year, of which 27 million are birds. This is only the number which were caught and brought home, though. We don’t know how many more cats caught, but didn’t bring back, or how many escaped but subsequently died.

The most frequently caught birds, according to the Mammal Society, are House Sparrows, Blue Tits, Blackbirds and Starlings whilst the most common garden birds are Wrens, Robins, House Sparrows, Woodpigeons (a bit big for most cats!), Chaffinches and Blackbirds. Make what you will of the disparity in the two lists! Bird behaviour has lot to do with which are caught, and I suspect that birds in an area with large numbers of cats will, over time, change their behaviour accordingly.

The RSPB say “We know that of the millions of baby birds hatched each year, most will die before they reach breeding age. This is natural, and each pair needs only to rear two young that survive to breeding age to replace themselves and maintain the population. It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season, so cats are unlikely to have a major impact on populations. Those bird species which have undergone the most serious population declines in the UK (such as Skylarks, Tree Sparrows and Corn Buntings) rarely encounter cats. Research shows that these declines are usually caused by habitat change or loss, particularly on farmland.”.

What can cat “owners” do to reduce predation levels?

Number one must be to keep them in at night: it helps; we did so with our cats all their lives. This is particularly important during the breeding season when there are fledglings around. Inexperienced and hungry young birds, desperate for their first feed of the day are easy prey, and parent birds are all too willing to risk their own lives when feeding offspring. Lights out and cats out at bedtime is not a good idea!

Collars fitted with bells or sonic devices have also been shown to reduce predation rates. It may take a cat a few days to get used to one though…

If you’d like to read further, try Floyd, L., Underhill-Day, J. C. (2013). Literature Review on the effects of cats on nearby protected wildlife sites. Unpublished report by Footprint Ecology for Breckland Council.

If you find the lives of our garden birds to be of interest, and would like to join in and count the feathered occupants of your garden, please contact me or visit the BTO Garden BirdWatch website (www.bto.org/gbw). Membership is free for the duration of the Covid lockdown

Mike Gray

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