CUCKOO: treacherous visitor on a deadly mission

DESPITE their welcome calls each spring, cuckoos would soon be given short shrift if their ruthless trickery was translated to the human world. The cycle of treachery begins with the mother cuckoo sneakily laying her own egg in the nest of another bird and abandoning it to its fate.

This egg is a timebomb which is primed to explode into life as quickly as possible, something often achieved before the eggs of the host bird hatch. From then on the ferocious cuckoo chick concentrates on expelling from the nest all other eggs or chicks it finds around it - and it will not rest until this is accomplished.

Genuine offspring unfortunate enough to be pushed from the safety of the nest are, of course, doomed.

In the grotesque charade that follows, the cuckoo chick somehow manages to dupe its new parents - often tiny meadow pipits or reed warblers - into treating it as their own.

The conned parents exhaust themselves rearing a fledgling that becomes so large it eventually fills the entire nest.

Yet they continue slipping more insects into its gaping mouth until it chooses to leave.

The parasitic behaviour of cuckoos was first observed and recorded in the 18th century by Dr Edward Jenner, the man who went on to discover a vaccination for smallpox.

How cuckoos came to perfect their technique for leeching off other birds remains a mystery but perfect it they have with lethal success.

Even their appearance is a sort of con-trick because adult cuckoos actually look like sparrowhawks in flight and, as such, are given a wide berth by large birds which might otherwise attack them.

This particular trick can sometimes backfire, however, when smaller birds gang up to mob them, as they would an owl or hawk.

Although their distinctive call carries far, cuckoos are surprisingly difficult to spot and I have enjoyed good views of them on only a few occasions.

The male cuckoo actually makes the 'cu-coo' call while the female emits an unusual bubbling sound.

Cuckoos are migratory and normally make it to our shores at the end of April after spending the winter in Africa.

By September, most will have left again.

The diet of adult cuckoos consists of hairy caterpillars which are avoided by other birds because their cumulative effect is poisonous.

Yet cuckoos boast another modification to help them survive even this - an especially thick stomach lining which can be shed and renewed.

A few years ago, an opinion poll was conducted by Mori which asked which bird had the most beautiful song or call.

The winner was the song thrush but the cuckoo still featured in the top 10. Despite its nasty habits, we love the cuckoo's haunting call.