Cat Hunting by Jsome at flickr (24960)

There are several subjects which are extremely difficult to discuss because even a mention raises emotions. One such topic is the domestic cat and its impact on the environment.

To explain my standpoint first, I love all animals and as a result have started to design my garden to favour wildlife. So far I have had some success with two hedgehogs living under my shed and dozens of birds visiting my feeders and birdbath daily. There is a threat to my plans however. The vicinity of my home is overpopulated with cats. These are not feral cats as far as I can tell but domestic cats let lose by their owners. Many times these creatures have entered my garden to hunt and have scared the birds away: indeed, many times they have killed the very birds I have been attracting.

As a result I have been researching the best ways to discourage cats from my garden, something I will cover later, but I also started to consider the wider picture: are cats introduced by humans having an overall impact?

Of course I will be looking from my position in Britain but this is clearly a consideration throughout the world. It is difficult to estimate the global domestic cat population, as there are so many feral and stray cats, which indicates one of the problems immediately, but it is estimated there are in excess of 76 million in the USA (the largest singe population) and 7.7 million in the United Kingdom.

The British Mammal Society reported in 2001 that cats were annually responsible for the deaths of an estimated 200 million mammals, 55 million birds, 10 million reptiles and amphibians and 10 million other creatures in this one country alone. Columbia University's Introduced Species Summary Project revealed that the Guadalupe Storm Petrel and at least three other seabirds became extinct in the islands off the California coast through predation by cats. The Audubon Society estimates the US population of cats kills several billion small animals every year. Reports from Australia, New Zealand and Mauritius indicate that several native bird species have also been exterminated in the same way.

The BBC wildlife presenter Chris Packham is a particular critic of cats. "We have got to face up to the fact that the devastation of our wildlife by these serial killers is a serious problem that has to be tackled." He suggests a licensing system similar to that used for dogs and a widening of an Australian scheme that rounds up cats found outside their home properties at night. The British Trust for Ornithology has echoed his views and Wildlife Trusts around Britain have also acknowledged the problem, particularly as cats have threatened bat conservation projects.

Intriguingly The Royal Society For The Protection of Birds is more conciliatory about the impact cats have on the bird 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." They do concede cats are a problem in some vulnerable habitats though. This relaxed attitude may indicate one of the problems of the argument: some environmentalists are cat owners too.

Domestic cats kill not for food but for sport and to satisfy their natural instincts. Frequently they play with their prey for up to thirty minutes before killing them. Derek Conway, the Chief Executive of the Cats Protection League charity, says "Humans should stop playing God with nature. The feline's instinct is to hunt and it is wrong for humans to attempt to intervene in that natural order. Part of the charm of a cat is its natural behaviour." Unwittingly Mr Conway has established the problem. Mankind is playing God by introducing a large number of cats to the natural environment. However 'natural' they may be they are still an invasive species alien to the natural ecosystem. This was always going to upset the delicate natural order and environmental balance. The problem is, as always, with irresponsible cat owners.

Derek Conway also supports a curfew for cats as he recognises a problem irresponsible cat owners have. When such people allow their cat to roam they somehow think it will be safe. Cats regularly disappear however and this is because they are entering the realm of the wild with its dangers including cars and competition. Depending on where you are in the world there are other animals that may consider cats part of the food chain. Equally evolution is ensuring cats do not have it all their own way: I have witnessed magpies attacking and chasing off a cat for example.

There is clearly a need to control cats more, whether you are a cat owner or consider them a problem. However it should be borne in mind cats can have a limited use especially in reducing rat populations.

Cat owners should consider not releasing their pet into the outside world, certainly at night, or at least should fit them with a collar with a bell or electronic alarm so wildlife can hear them approaching.

The Columbia University report notes that sterilization is an option and this has been enforced by several local authorities around the world, particularly against feral cats. On Marion Island off the southern coast of Africa all cats were entirely eliminated. Obviously it would be preferable if owners took responsibility for their own cats and leave the authorities to deal with feral felines.

If you find cats to be a pest in your garden there are several humane methods to discourage them. Electronic sonic devices can be quite effective, as can peppers and sprays, although the latter need respreading after a fall of rain and some brands can discourage other animals and birds too. Some plants can be used particularly prickly varieties, which the cats find uncomfortable. Cats supposedly dislike Rosemary and some mints too. Keeping a dog would also discourage them.

When I started my research into the excess numbers of cats I was expecting to find I was wrong but was surprised at the evidence showing there is a problem. Softhearted cat owners believe themselves to be animal lovers but forget their fluffy pet hunts and kills other animals. No matter where you are in the world if you release your cat outside you endanger much of the wildlife in the vicinity.

Nobresca by irene nobrega at flickr