The onset of spring in Britain may come quietly this year due to dwindling numbers of cuckoos, conservationists said. The Woodland Trust said numbers of the gray birds, beloved by Britons for announcing the end of winter with their distinctive cooing, has fallen by up to 60 percent since the 1970s. Amid fears cuckoos are falling victim to an ever more unsettled climate and aggressive modern farming methods, the charity asked Britons to go on alert for the noisy birds. "Everyone is needed to listen out for the first cuckoo they hear," the Trust said in a statement. "Even if you usually hear the cuckoo, but don't hear one this year, please let us know." Infamous for their habit of laying eggs in other birds' nests—a hen cuckoo can swap another bird's egg with her own in just 15 seconds *—the birds have always held a special place in British hearts as harbingers of spring. The Woodland Trust and the British Trust of Ornithology want nature-goers to send them information about cuckoo-sightings for a survey on changes to Britain's seasons. They have also asked for news of the arrival of swifts, swallows, bumble bees, queen wasps, and daisies.