Factors affecting natal and breeding magpie dispersal in a population parasitized by the great spotted cuckoo

Understanding the causes and consequences of avian dispersal is important since dispersal movements may influence individuals’ survival and reproductive success. Although obligate interspecific brood parasitism has obvious detrimental effects for its avian host, few empirical studies have addressed the question of how brood parasitism may influence host dispersal. We studied factors affecting, and consequences of, natal and breeding dispersal movements in a population of magpies, Pica pica, parasitized by the great spotted cuckoo, Clamator glandarius, by monitoring dispersal of individuals and cuckoo parasitism over 6 years. Recruitment probability increased with fledging weight and was higher for individuals hatching early in the breeding season. Heaviest recruits at fledging settled closer to their natal nests and bred in more saturated sites within the study area. Natal dispersal distance did not predict the magpie’s productivity or risk of cuckoo parasitism in its first reproductive attempt. Females and parasitized males decreased their breeding dispersal distance when breeding close to other pairs, whereas nonparasitized males breeding close to other pairs dispersed more in subsequent years. Females, but not males, breeding closer to their previous breeding places had larger clutches than those breeding further away. Dispersing longer or shorter distances between breeding attempts had no consequences in terms of cuckoo parasitism avoidance for magpies. Our results suggest a minor role of great spotted cuckoo parasitism on magpie dispersal movements at the spatial scale analysed. Instead, our study revealed density-dependent dispersal in our parasitized magpie population.