Cats: furry friends or natural born killers?

In our latest Friday science feature from a lecturer at the University of Huddersfield, Professor Robert Smith looks at so-called ‘wildlife management’ as a way of keeping pests under control and preventing other animals from disappearing

Joanna Lumley loves cats — as do millions of others. You may have seen her TV programme on cats on Sunday.

Cats belong to the group of animals called mammals — the warm, furry animals that most people like.

Dogs and cats are probably our most popular pets. Hamsters, horses and even ferrets also figure in any pet popularity table you might find on the internet.

Yet not all mammals are so popular. Rats are feared and disliked by most people, rabbits are major pests of farming and deer can cause huge losses in both farming and forestry.

Even cats are disliked by many because they kill 50 to 60 million birds every year in British gardens.

One person’s warm, furry pet can be the next person’s natural born killer. It all depends on what the animals are doing, how many there are and also where they are.

Wild animals are often in conflict with people and are then thought of as pests.

Rats are feared because they spread disease. Both rats and rabbits destroy valuable food crops and moles spoil golf courses.

Wild animals can also be a source of food. Rabbit, hare and venison are all popular items on restaurant menus because the meat is both healthy and flavoursome.

Is it possible to “manage” wildlife populations, either to keep pests under control or to ensure a sustainable supply of food from wild animals?

Or do populations of animals go up and down randomly so that it is not possible to manage them sustainably?

About 20 years ago, I set up a new postgraduate course in wildlife management at another university.

The course was based around two key principles. The first of these is that all animal populations are limited by various factors (often food, space, predators or disease) and that animal numbers can be managed by managing the limiting factors.

The second is that almost all animal populations produce surplus offspring, most of which are doomed to die young.

The doomed surplus can be a harvest (if you are culling wildlife such as deer to produce meat, for example) and the harvest is sustainable if you do not take more than the surplus.

Oceanic fisheries were sustainable for centuries until we became too greedy. Many fish stocks are now endangered because fishing fleets have taken the breeding stock as well as the surplus.

The other side of this coin is that, if you want to reduce numbers of a pest such as rats to a lower level, it is no use only removing or killing the doomed surplus because there is no long-term effect.

When animals invade a new environment, they often increase and become a pest if limiting factors such as predators do not travel with them.

Examples in Britain include the grey squirrel from North America and the muntjac deer from Asia.

Both cats and rats have driven birds to extinction on many islands across the world after they walked or swam ashore from ships.

Trapping, poisoning or shooting will have limited effect on these invaders if only the surplus is removed.

Modern wildlife management uses a variety of new methods that are more effective in the long-term than simply killing pests.

For example, feeding badgers to make them healthier may reduce cross-infection of TB between badgers and cattle.

Birth control is being developed to reduce numbers of re-introduced wild boar in Britain.

Research has shown that managing the farm habitat to make it less attractive for rats can be as cost-effective as poisoning.

Animal populations do go up and down in nature, but wildlife managers are now able to keep pests under control and to prevent other animals from disappearing by applying modern scientific principles.

Thus is true that pet cats kill millions of garden birds every year but they do not cause British bird populations to decline because they kill the surplus that would die young anyway.

The sorts of birds that are in decline Britain are affected much more by loss of habitat than by cats.

Cats are still natural born killers but they are also well-loved companions for many of us.