Effect of great spotted cuckoo presence on magpie rejection behaviour

Soler & Moller (1990) reported that egg rejection of great spotted cuckoo Clamator glandarius eggs by magpies Pica pica varies between populations depending on the duration of sympatry. Here, we test experimentally the idea that differences in ejection rates between areas of presumably different duration 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 magpie nest does not increase the probability of egg rejection.