Brood parasitism and proximity to human habitation

Humans provide safe refuge against many species such as birds of prey because such species keep a safe distance from humans. We hypothesized that many suitable host species for brood parasites similarly seek refuge in the proximity of humans to avoid parasitism. In 2 study areas sized 50 km2 in Denmark and France that consist of half urban habitats and half rural habitats, more than 77% of all birds were located within a distance of 100 m from the nearest inhabited house. Consistent with our hypothesis we found that brood parasitic common cuckoos Cuculus canorus kept a longer mean distance from human habitation than did numerous potential host species that generally nest close to human habitation. Thus, parasitism rate increased with increasing distance from human habitation. In an intraspecific study of the Oriental reed warbler Acrocephalus orientalis, we showed that parasitism rate increased with distance from the nearest human habitation, and individuals of this species were disproportionately aggregated near human habitation. Because numerous bird species have evolved close proximity to humans, we hypothesize that avoidance of brood parasitism is an important selective force having contributed to this pattern of microgeographic distribution.