Effect of great spotted cuckoo presence on magpie rejection behaviour

Soler & Moller (1990) reported that egg rejection of great spotted cuckoo C lamator glandarius eggs by magpies Pica pica varies between populations dep ending on the duration of sympatry. Here, we test experimentally the idea t hat differences in ejection rates between areas of presumably different dur ation of sympatry could be due to a conditional response by magpies to the presence of adult parasites near the nest. The rate of ejection of mimetic cuckoo egg models was identical in both treatment groups, independently of whether or not the cuckoo was presented at the same time as the model egg. Thus, we conclude that the presence of a great spotted cuckoo near the magp ie nest does not increase the probability of egg rejection.