The iconic cuckoo is in danger of vanishing from Britain after the population dropped by a fifth in one year, experts warned today.
Numbers of the migrant bird fell by a shocking 21 per cent between 2008 and 2009, according to the Breeding Birds Survey (BBS).
Cuckoos have been designated a ”red-list” species by the Royal Society for the Protection of Birds (RSPB) – meaning that more than half of the population has disappeared in the past 25 years.
Damage to the bird’s winter habitat in West Africa and a decline in the large insect species it eats while on British soil are being blamed for the downturn, although experts still maintain there could be other reasons.
RSPB spokesman Tony Whitehead said: ”There are two possible reasons – the first has to do with the fact that the bird is struggling in the place that it winters, because of course they’re migrants.
”They base their winters in West Africa in an area where there’s a lot of deforestation going on, lots of change to land because of agriculture, and that brings with it all sorts of problems.
”The second reason is that cuckoos when they come here they feast on large insects, especially caterpillars.
”Some of those, such as the caterpillars of the Garden Tiger Moth, are species that are also declining. So it’s almost like a double whammy for the bird.”
The report – published jointly by the RSPB, the British Trust for Ornithology, and the Joint Nature Conservation Committee – also shows that the species is down 44 per cent since 1995 when the BBS began.
The survey is conducted by hundreds of volunteers who monitor randomly-chosen 1km-square zones between April and June.
Volunteers make two early-morning visits to their allocated square and record all birds encountered there while walking two 1km transects.
For the 2008-2009 survey the most significant decline in cuckoo population was recorded in the South West region, where numbers dropped by a shocking 71 per cent.
Mr Whitehead added: ”Many migrants are very, very faithful to the places they go, right through the generations.
”If a population through an English region like the South West is going to a very specific place in Africa and something completely alters that landscape then that population is going to have a problem.
”The South West is declining more than the other regions.
”The cuckoo’s iconic song was once a common sound over much of the region, heralding summer and the return of warmer weather.
”Nowadays though, you’ll be unlikely to hear a cuckoo anywhere away from the region’s uplands and heaths.
”So much more research needs to be done into this. If this trend continues they will either disappear altogether or just hang on in one or two places.”
The survey also found three other red-list species – the Grey Partridge, the Lapwing and the Starling – have decreased significantly between 2008 and 2009.
The Marsh Tit was the only red-list species to have shown a significant increase.
The national population of kestrals, an ”amber-listed” species, plummeted by 36 per cent over the period.
Cuckoos arrive in the UK in late March or early April and depart in July or August, with young birds leaving a month or so later.
They are found across the UK, with an estimated 9,600 to 20,000 pairs breeding every year.
The blue and grey dove-sized birds are brood parasites, with the females laying their eggs in the nests of other birds, especially meadow pipits, dunnocks and reed warblers.