Conservationists fear that the cuckoo is in sharp decline
Spring across much of the UK is noticeably quieter than it used to be. One of the most evocative vernal sounds, the call of the cuckoo, is becoming much rarer.
Since the early 1970s, conservationists say, cuckoo numbers in farmland areas have fallen by 20%, and in woodland by 60%.
They want people across Britain to listen out for cuckoos this year.
The fall in the bird's fortunes emerges from a survey by the British Trust for Ornithology (BTO).
Reed warbler target
Both the Woodland Trust and the BTO are urging people to report sightings - or more likely hearings - of the cuckoo, and also to report its absence from its normal haunts.
They say: "The cuckoo, which resembles a sparrowhawk or a kestrel in flight, can be difficult to identify.
"However, it would be very hard to mistake the distinctive song of the male and the unmistakable bubbling noise of the female as they exchange calls during courtship."
The cuckoo is known chiefly for its habit of laying its eggs in other birds' nests. Among British birds it targets reed warblers, meadow pipits, wrens and dunnocks.
The hen cuckoo spends hours watching its chosen host's nest, and then replaces the original egg with its own in as little as 15 seconds.
Climate change
Occasionally it makes the mistake of choosing a host that has learned how to identify cuckoo eggs and to reject them. But if a young cuckoo hatches successfully, it will spend a lot of energy pushing the host's eggs and chicks out of the nest.
The Woodland Trust believes that trees and woods are very susceptible to climate change, and that this may help to explain the birds' plight.
It says ancient woodland is also becoming increasingly fragmented and isolated, and much less friendly to many birds. It believes cuckoos may be facing a reduction in host nests, a loss of suitable habitat, and an unpredictable food supply.
The Woodland Trust and the BTO want observers to send them information about the cuckoo to feed into a survey of phenology, the study of the timing of seasonal natural events.
The survey will build on data collected since 1736, and the organisers also want information about the time that birds like swifts and swallows arrive in the UK from their winter quarters.
They want to know when flowers such as bluebells, ox-eye daisies and dog roses emerge, and when bees, wasps, ladybirds and other insects appear.