Is the cuckoo clocking in too late?

May 2010: Breeding cuckoo numbers have dropped by two thirds over the past 25 years - and researchers believe climate change may be to blame.

Birds whose nests cuckoos will traditionally use, such as the dunnock and meadow pipit, are nesting earlier, and researchers at the British Trust for Ornithology wondered if the cuckoo was now arriving back in the UK too late.


The cuckoo is one of the UK's best-known summer visitors, returning from West Africa during late April and early May to breed. It is a brood parasite, laying its eggs in other birds' nests. The top four host species are dunnock, pied wagtail, meadow pipit and reed warbler and this latest study examines whether changes in the abundance of these species, or the timing of their breeding were having an impact on the cuckoo's decline.

Yet of the four main host species there has been a decline only in the meadow pipit, which researchers say accounts for just one per cent of the falling number of cuckoos. Dunnocks, pied wagtails and reed warblers are all now nesting five to six days earlier, but although dunnock and pied wagtail nests were likely to be less available to the cuckoo as a result, said researchers, the reed warbler breeds late, and so when it nests early it works to the cuckoo's benefit.

Cuckoo decline remains a mystery
Researchers concluded that neither the abundance of the host species, nor their change in breeding patterns were significant enough to fully account for the rapid decline in cuckoo numbers.


Stuart Newson, Senior Research Ecologist at the BTO said: ‘Host availability does not appear to be a major drive of cuckoo declines, so we are left with a smaller number of possible explanations. Given cuckoo breeding ecology and migration strategy, these include reduced prey (mainly caterpillars) availability during the breeding season or the deterioration of conditions along migration routes or on over-wintering grounds in sub-Saharan Africa. These should be the focus of future work into the decline of this charismatic species.'

Cuckoos which breed in Britain during the summer overwinter in West Africa, where increasing agriculture and forest clearance are causing significant land-use changes and loss of habitat. These regional changes reflect a growing global demand for food, timber and bioenergy. BTO's long-term research partner, JNCC, is investigating the impacts of such drivers on global ecosystems and their impacts on local biodiversity, including migratory species which visit Britain.

The BTO is carrying out research on migrant birds in West Africa to identify the pressures these birds face there during the winter months. For more information visit www.bto.org/appeals/out_of_africa_appeal.htm