Cuckoos, recognisable by their familiar call that for many heralds the start of spring, are summer visitors to locations throughout Britain, especially central and southern England. They are also infamous brood parasites, meaning that females lay their eggs in the nests of other birds, leading to them unknowingly rearing the chick. In the UK host species are primarily the Meadow Pipit, Dunnock, Pied Wagtail and Reed Warbler. Once hatched, the cuckoo will evict the legitimate chicks from the nest, enabling it to dominate the food supply from the host parents. For this to be successful, the timing of the cuckoo laying the egg is crucial, so that the cuckoo will hatch before the other eggs in the nest, allowing it to remove the competition as soon as possible. Research has shown that cuckoos carry out ‘internal incubation’, delaying laying by up to 24 hours, which causes the chicks to develop more quickly and therefore hatch earlier . Despite cuckoos exploiting the parental behaviour of other bird species, a recent study shows that some cuckoo chicks can deter nest predators, which can improve host reproductive success , suggesting this relationship could be mutually beneficial.
— Wildlife Sightings (@wildlife_uk) June 13, 2014
Cuckoos are a red list species due to a dramatic decline in numbers, with over half the cuckoos in the UK being lost in the last 25 years. The reason for this remains unknown, although it has been suggested that declines in host abundance, changes in timing of host breeding and change in land use could be causes. Reduction in host abundance and changes to their breeding time due to climate change could reduce the number of available nests for cuckoos use. During a study between 1994 and 2007, the Meadow Pipit population was the only one to have declined out of the four main host species and this only accounted for 1% of the observed decline in cuckoo numbers. Also, it was found that Dunnocks, Pied Wagtails and Reed Warblers breeding time has shifted forward by 5-6 days, which could have reduced available nests for cuckoos . Another potential cause is land use change and agricultural intensification, which is a major global driver of habitat loss. Research has suggested that cuckoo declines could be due to declines in prey species, predominantly large, hairy moth caterpillars, which have lower abundances in farmland. Therefore increasing prey abundance by maintaining semi-natural habitats may be a potential immediate strategy to conserve cuckoos, and measures under agri-environmental schemes (compensate farmers for any loss of income associated with measures that benefit the environment) that increase moth abundance may offer a longer term solution . Despite the uncertainty over the causes of cuckoo decline, we can be sure that without any intervention the familiar call of the cuckoo will disappear from the UK.
 Birkhead TR, Hemmings N, Spottiswoode CN, Mikulica O, Moskat C, Ban M, Schulze-Hagen K (2010) Internal incubation and early hatching in brood parasitic birds. Proceedings of the Royal Society of Biological Sciences doi: 10.1098/rspb.2010.1504
 Stevens M (2014) Evolution: Predator versus Parasite. Current Biology 24:388-390
 Douglas DJT, Newson SE, Leech DI, Noble DG, Robinson RA (2010)How important are climate-induced changes in host availability for population processes in an obligate brood parasite, the European Cuckoo? Oikos doi: 10.1111/j.1600-0706.2010.18388
Denerley C (2014) The impact of land use change on a brood parasite system: cuckoos, their hosts and prey. PhD Thesis, University of Aberdeen)
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