THE cuckoo has been a herald for spring for centuries but its numbers are in such decline that it could soon join the list of most endangered species.

Research from the British Trust for Ornithology suggests that the bird is unlikely to return to many of its favourite annual haunts.

In the 1960s there were some 35,000 breeding pairs spread throughout Britain, but experts believe that the population has declined to between 10,000 and 20,000 pairs.

One possible reason for the drop in population is a lack of “foster parents” to rear the cuckoo’s chicks. The bird lays its eggs mainly in the nests of the dunnock, the meadow pipit and the reed warbler. The number of dunnock, which tend to thrive in rural gardens, declined by 40 per cent between 1967 and 2002. Similarly the meadow pipit, which nests in upland, moor and healthland, is down by 40 per cent.

While the reed warbler has increased by 80 per cent in the same period, they nest near wetlands and marshes. These tend to be remote places away from populated areas and so cuckoos reared in these areas are not easily spotted or heard.

The cuckoo, Cuculus canorus, is also believed to suffer from drought in northeast Africa where it spends the winter. Other species wintering in this area may also be affected by the lack of water and insects to eat. Experts are concerned about the red-backed shrike, which is now virtually extinct in the UK, the marsh warbler, which is down to between 4 and 30 breeding pairs, the lesser whitethroat, which has 64,000 pairs but is down by 20 per cent in 25 years, and the wood warbler, which dropped 63 per cent between 1994 and 2003 and is down to between 9,000 to 11,000 pairs. There is also a loss of habitat in many parts of Britain that is affecting the number of black hairy caterpillars, the cuckoo’s food of choice.

David Glue, a BTO researcher, has noticed the decline in cuckoos after monitoring the species for 35 years. Last year not one cuckoo appeared at his own Common Birds Census plot at the Aylesbury sewage treatment works in Buckinghamshire. He believes that this is because of the lack of caterpillars for food. These thrive on damp pasture, thickly hedged farms, heaths, commons, large mature gardens and woodland fringes, but there has been a loss of these habitats following new farming patterns.

The BTO wants to collect more details about the plight of the cuckoo, so that conservationists can help to retain “the cuckoo’s charismatic sight and sounds”. The bird is on the amber list, which notes concern about a species, but it may be included in the red list of most threatened birds next year.

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