ARCTIC Autumn and Winter Movements and Sexual Segregation

ABSTRACT. Willow ptarmigan (Lagopus lagopus alexandrue) in northern British Columbia leave their breeding areas during autumn and winter. The movements differ between males and females. In this study I examine the causes and extent of these differences. Ptarmigan did not leave their breeding grounds immediately after the breeding season, but remained on or near their territories until December. After chicks fledged, part of the population moved uphill from their territories. Coincident with moult into winter plumage, ptarmigan moved farther from their territories. Both movements were probably to areas with better protection against predators. After moulting, all tagged males and half of the tagged females returned to their te ritories, and males resumed territorial display. Ptarmigan remained on their t rritories until increasing snow cover depleted cover, forcing them to leave. Males left the breeding grounds later than females and returned earlier in spring. In winter females moved farther than males, supporting the reproductive strategy hypothesis, but segregation was not complete. Sexual segregation may not be related to migration alone, but could occur at any time ptarmigan are in flocks. Key words: willow ptarmigan (Lagopus lagopus alexandrue), autumn territoriality, winter movements, sexual segregation, northern British Columbia RÉSUMÉ. Le lagopede des saules (Lagopus lagopus alexandme) de la Colombie-Britannique septentrionale quitte son aire de nidification durant l’automne et l’hiver. Les dkplacements du mille different de ceux de la femelle. Ces recherches portent sur le degr6 et les causes de cette difference. On a trow6 que le lagopede ne quitte pas son aire de nidification imm6diatement aprks la saison nidificatrice. Il reste sur son territoire ou 1 proXimit6 jusqu’au mois de d6cembre. Aprks que les jeunes se sont emplum6s, une partie de la population migr