Territorial behaviour of the Hen Harrier in winter

摘要

Observations in central Europe suggest that the Hen Harrier Circus cyaneus shows marked territorial behaviour in the wintering grounds. During the day, dominant females occupy the best feeding areas (with high vole densities) and defend them, primarily against conspecifics but to some extent also against other raptors. Subdominant females and all males are attacked by dominant females and evicted from defended territories, and sometimes their prey is stolen. Territorial behaviour is expressed throughcertain interactive behaviour, specific calls and a distinctive posture termed the 'Kong' display by the author. Males are generally confined to more peripheral or suboptimal areas.The hypothesis that similarity in plumage between young males and adultfemales could represent a form of mimicry is discussed. Agricultural intensification may have increased the natural winter territorial behaviour of Hen Harriers; loss of habitat diversity seems to have had a negative impact on males in particular. The greater risk of predation for males and young birds, combined with the need to expend more energy while hunting, may affect overwinter survival rates and in turn have an impact on population dynamics on the breeding grounds, notably the occurrence of polygyny.