For centuries, the call of the Cuckoo has been considered a harbinger of spring. The bird’s arrival was once so keenly awaited that April 14 was designated Cuckoo Day because the first Cuckoo was usually heard on or about that day in southern England.
According to an old verse, the Cuckoo sings from St Tiburtius Day to St John's Day — ie, from Cuckoo Day, which is also the feast day of St Tibertius (a Christian martyr in ancient Rome), to June 24, which is Midsummer Day and the feast day of St John the Baptist.
Why the June 24 cut-off? Since the Cuckoo is a brood parasite — relying on other birds to raise its young — it has no breeding territory to defend and so has no need to continue singing further into the summer.
But today the call of the Cuckoo is far from common. The species has been in decline for 50 years or so, and since the early 1980s its population has dropped by two-thirds. In 2009 it was added to the UK red list of Birds of Conservation Concern.
The reasons for the Cuckoo’s decline are not known. Some people have blamed it on the destruction of the habitat of the small birds that find themselves fostering young Cuckoos. However, this is unlikely because none of the main host species — the Meadow Pipit, the Dunnock, the Reed Warbler and the Pied Wagtail — is also in significant decline.
Another possible cause is an increased use of pesticides on farmland. This may have reduced the numbers of caterpillars, which are the Cuckoo’s main prey. But other birds that feed mainly on caterpillars have not shown such a sharp decline.
Climate change has also been suggested as a factor. Global warming has certainly shifted forward the host birds’ breeding by a few days, but there is no evidence of any link to the Cuckoo’s decline.
With no specific evidence of problems in the bird’s summer haunts, we should perhaps be looking elsewhere. Major causes of decline may be the deterioration of conditions along the Cuckoo’s migration routes and problems within its over-wintering grounds in sub-Saharan Africa.