The distinctive call of the cuckoo was heard at the National Trust's Wicken Fen National Nature Reserve, in Cambridgeshire, for the first time this year (Monday 19 April), when three male cuckoos were spotted and heard calling from the trees over looking the mere on Adventurer's Fen.

Popular folklore says that the return of the cuckoo announces the arrival of spring. The Wicken Bird Ringing Club has been keeping detailed records of the arrival of the cuckoo and other migrant species dating back over 35 years. Analysis of these records reveals an average arrival date of 19 April each year for the cuckoo.

The European cuckoo is about the size of a dove and both sexes have bluey-grey backs and heads, with brownish white barred chests. They spend most of the year in Southern Africa returning to Britain in April to breed. The cuckoo population has declined by a worrying sixty percent in the last 30 years but thankfully Wicken Fen remains one of their strongholds with around 8 breeding females returning to the fen each spring.

Throughout the breeding season male cuckoos can be seen perched prominent in tree tops, its tail cocked and wings drooped calling to attract a mate. A good place to spot cuckoos is from Wicken's Tower Hide overlooking Adventurer's Fen

Cuckoos are one of a handful of species throughout the world that are parasitic breeders. They lay their eggs in the nests of another species, leaving all the nurturing to the host species. Individual female cuckoos can only dupe one host species. At Wicken Fen, the hosts are reed warblers, but elsewhere throughout Britain the host species include dunnocks, meadow pipits and pied wagtails.

A female, heavy laden with egg, stakes out the warblers tiny intricate nests from the trees above the reed lined Lode banks and ditches where they nest. The moment they leave the nest unguarded she will swoop down lay her egg and remove one warbler egg, the whole process taking as little as 10 seconds. Her egg will mimick the warblers greenish eggs, albeit somewhat larger.

It is perhaps one of nature's great mysteries - why do the warblers incubate an egg clearly much larger than their own - or look after a chick so obviously unlike their own. Once hatched the cuckoo chick has one thing on its mind - murder! Naked and blind it struggles to remove any un-hatched eggs and young warbler chicks from the nest to eliminate competition for food. In only two weeks, the young cuckoo will have virtually outgrown the nest and will already be about three times the size of the adult warbler with an appetite to match.

The last calls of the cuckoo are heard in early July as the adult birds depart after their brief stay for their return journey to Southern Africa. Their young fledglings will remain under the care of the warblers and will eventually head south themselves in August or September -hopefully to return to Wicken Fen next spring.

Notes to Editors

1. The table shows the mean arrival dates for some of Wicken's leading migrant bird species.

2 Wicken Fen was purchased by the National Trust in 1899, the first Nature Reserve owned by the Trust. It is widely regarded as the most species rich nature reserve in the country with over 8200 recorded species.

3.The National Trust is Europe's biggest conservation organisation and looks after special places across England, Wales and Northern Ireland for ever, for everyone. People and places are at the heart of everything it does. 3.5 million members, 50,000 volunteers, 500,000 school children, and millions of visitors, donors and supporters help the Trust look after its 300 historic houses and gardens, 700 miles of coastline and 250,000 hectares of open countryside.