No evidence for variable duration of sympatry between the great spotted cuckoo and its magpie host

Abstract

BROOD parasites and their hosts are thought to engage in a revolutionary arms race in which parasitism selects for adaptive defences by the host (such as egg rejection), which in turn select for counter-adaptations by the parasite (such as egg mimicry)^1,2. Soler and Mø11er have tested whether the duration of coevolution (measured by the duration of sympatry at three different geo-graphic areas) in a host–cuckoo system affected egg-rejection behaviour by hosts³. They found that the extent of both rejection and recognition of parasitic eggs covaried positively with the duration of sympatry. Here we show that, in the absence of strong historical evidence, field data do not support the existence of variations in the duration of sympatry at the two areas where the distributional ranges of the cuckoo and its hosts overlap. The reported differences in egg rejection by hosts might alternatively reflect flexible behavioural responses to the presence of the adult parasite near the nest.