Spatial patterns of egg laying and multiple parasitism in a brood parasite: a non-territorial system in the great spotted cuckoo (Clamator glandarius)

We analysed the spatial and temporal pattern of egg laying in great spotted cuckoo females using microsatellite typing to determine parentage of the e ggs and nestlings found in host (magpie) nests. The results showed that the re were no exclusive laying territories in the study area. Cases of multipa rasitism could be due to single females laying two or more eggs in a nest,o r to several females using the same nest. In the latter case multiparasitis m was due to a shortage of available host nests. We argue that the need for very large laying areas and the likely small cost of sharing parental care for chicks make the costs of defending territories higher than the benefit s, which has constrained the evolution of territoriality in this species.