Why does a cat wag its tail when it is hunting a bird on a lawn?

The scene is familiar to most cat-owners. Through the window they see their cat stalking a bird by creeping stealthily towards it, head down and body low on the ground. This cautious crouching attempt to be as inconspicuous as possible is suddenly and dramatically ruined by the animal's tail, which starts swishing uncontrollably back and forth through the air. Such movement acts like a flag being waved at the bird to warn it of approaching danger. The intended victim takes off immediately and flies to safety, leaving a frustrated feline hunter staring up into the sky.

Cat-owners witnessing this scene are puzzled by their cat's inefficiency. Why does the cat's tail betray the rest of the body in this self-defeating way? Surely the wild ancestors of the domestic cat could not have survived such a serious flaw in their hunting technique?

We know that conspicuous tail-wagging in cats is a social signal indicating acute conflict. It is useful when employed between one cat and another and is then an important part of feline body language. But when it is transferred into a hunting context, where the only eyes that will spot the signal are those of the intended prey, it wrecks the whole enterprise. So why has it not been suppressed in such cases?

To find the answer we have to look at the normal hunting sequence of the cat. This does not take place on an open lawn and is less well known to cat-owners than it might be because it involves a great deal of waiting and hiding. If owners do happen on a hunt in progress they will automatically disrupt it, so that there is nothing more to observe. The disturbed prey escapes and the cat gives up. So for a casual observer the whole sequence is not easy to study. It requires some systematic and secretive catwatching. When this is undertaken, the following points emerge:

First, the cat makes a great deal of use of cover. It spends much time lying half-hidden in undergrowth, often with only its eyes and part of its face visible. The tail is usually completely hidden from view.

Second, it never attempts to pounce on a prey until it is very close to it. It is not a prey-chaser. It may make a few stalking-runs, rushing forward in its flattened posture, but it then halts and waits again before pouncing. Third, its normal prey is not birds but rodents. A careful study of feral cats in the United States revealed that birds accounted for only 4 per cent of the diet. The excellent eyesight of birds and their ability to fly straight up in the air to escape make them unsuitable targets for domestic cats.

Together these points explain the dilemma of the suburban cat hunting a bird on a lawn. To start with, the open, manicured lawn robs the cat of all its natural cover, exposing its whole body to view. This is doubly damaging to its chances. It makes it almost impossible for the cat to creep near enough for its typical, close-quarters pounce without being seen. This puts it into an acute conflict between wanting to stay immobile and crouched, on the one hand, and wanting to rush forward and attack, on the other. The conflict starts its tail wagging furiously and the same lack of cover that created the conflict then cruelly exposes the vigorous tail movements to the frightened gaze of the intended prey.

If the attempt to hunt a bird on an open lawn is so doomed to failure, why does the cat keep trying? The answer is that every cat has a powerful urge to go hunting at regular intervals, but this urge has been severely hampered by advances in human pest control. In town and cities and suburbs, the rodent population that used to infest houses and other dwellings has been decimated by modern techniques. Garden birds may be pests, but their appeal to human eyes has protected them from a similar slaughter. As a result, the rodent-hunting cat finds itself today in an unnaturally mouse-free, bird-rich environment. It cannot utilize its natural hunting skills under such conditions. It is this state of affairs that drives the cat on to crouch hopelessly but compulsively on open lawns, staring longingly at elusive birds. So when it waves its tail at its prey on these occasions, it is not the cat which is a stupid hunter, but we who have unwittingly forced a clever hunter to attempt an almost impossible task.