THE EFFECT OF MAGPIE BREEDING DENSITY AND SYNCHRONY ON BROOD PARASITISM BY GREAT SPOTTED CUCKOOS

Nesting density and synchrony by hosts may indirectly serve as a defen se mechanism against brood parasites. Here we examine the relationship s between spatial and temporal distribution of host nests and the prob ability of being parasitized. We use as host species the Black-billed Magpie (Pica pica), a species that is parasitized by the Great Spotted Cuckoo (Clamator glandarius) in southern Europe. We also examined the differences in parasitism rate in nearby plots that differ in magpie social organisation. Results show that increased proximity to other ne sts and specially laying synchrony both reduced the probability of bei ng parasitized. Consequently, magpies breeding synchronously in dense plots may experience an indirect advantage against brood parasitism wi th respect to low density, low synchrony plots.