London, May 30: The cuckoo’s distinctive song, which heralds spring in Britain, may be heard less and less after the bird was placed on the endangered list today.

Out of 246 regularly occurring birds in the UK, 52 are now of the “highest conservation concern” and figure on the “red list”.

Along with the cuckoo, today’s expanded list of endangered species includes the lapwing and yellow wagtail. They join others such as the turtle dove, grey partridge, house sparrow and starling which were on the previous list drawn up in 2002.

Alarmingly, says the Royal Society for the Protection of Birds, red listed species now account for more than one in five (21 per cent) of all the UK’s bird species. This is a far higher proportion compared to the last assessment when 40 species (16 per cent) were red listed. Most species on the red list have suffered a recent halving of range or population in the UK.

It is not clear why cuckoo numbers have fallen so sharply but, according to Grahame Madge of the RSPB, research by conservationists will examine whether there are problems with habitat either in the UK or in sub-Saharan Africa, where the bird spend their winters, or on their migration route.

The cuckoo relies heavily on hairy moth caterpillars for food, and with many species of butterfly and moth also in decline, lack of food could be responsible.

Madge said: “One fact about the cuckoo most people know is it lays its eggs in other birds’ nests, and two key hosts, the meadow pipit and dunnock, are birds that are also in decline. We’re wondering whether the decline of its hosts could be leading to a decline of the cuckoo itself.”

RSPB conservation director Mark Avery said it was “scandalous” that a growing number of charismatic, widespread and familiar birds needed urgent help.

The “most shocking” decline was that of summer-visiting birds such as the cuckoo, which had seen numbers fall by 37 per cent over the last 15 years, he added.

The latest assessment, formally called “Birds of Conservation Concern 3”, has been compiled by a partnership of organisations including the RSPB, Game and Wildlife Conservation Trust, Joint Nature Conservation Committee, Natural England, Scottish Natural Heritage and the Wildfowl and Wetlands Trust.

India, too, has serious problems with familiar species, notably the vulture, on which RSPB researchers have been working in West Bengal, Assam and others parts of the country.