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SOCIAL ORGANIZATION, MOVEMENTS, AND HOME RANGES OF BLUE GROUSE IN FALL AND WINTER

SOCIAL ORGANIZATION, MOVEMENTS, AND HOME RANGES OF BLUE GROUSE IN FALL AND WINTER,JAMES E. HINES

SOCIAL ORGANIZATION, MOVEMENTS, AND HOME RANGES OF BLUE GROUSE IN FALL AND WINTER   (Citations: 1)
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ABsTRKr.-Social organization, movements, and home ranges of Blue Grouse (Den- drugupus obscurus) were investigated on Hardwicke Island, British Columbia from 1979 to 1982. Most broods disbanded by the end of September, and young grouse did not associate with their mothers or siblings in winter. The tendency to form flocks was lowest in fall. Grouping increased gradually until midwinter and then declined until spring. Approximately half of the grouse observed during winter were in groups that usually consisted of 2 or 3 birds (X = 2.9 + 0.1 (SE), N = 210). Daily movements were usually small during winter (median = 69 m) and home ranges averaged 16.8 f 2.3 ha (N = 2 1). Although Blue Grouse did not show the strong segregation of sexes found in some other tetraonines, birds most frequently associated with individuals of their own sex and age. The partial segregation of grouse by sex and age may have resulted because females wintered at lower elevations than males and juveniles migrated longer distances than adults. Segregation of sexes of other species of grouse may be explained by a similar mechanism. Block formation is most frequent in species of grouse that winter in open areas and less frequent in species that winter in forests. Received 20 Sept. 1985, accepted I8 Feb. 1986. Studies of the social organization of grouse and other birds have usually emphasized the breeding season, with mating systems drawing particular attention (Wiley 1974, Wittenberger 1978, Oring 1982). The nonbreeding season is thought to be a critical period for mortality in avian populations (Lack 1954, 1966; Bendell 1972; Fretwell 1972), and selective pressures during fall and winter may be important in shaping the overall patterns of avian sociality. During winter, many species of grouse tend to form single sex flocks. A possible proximate explanation for this segregation is that the sexes migrate different distances or prefer different kinds of habitats and hence are not in contact with each other during winter (Koskimies 1957, Weeden 1964, Irving et al. 1967, Hoffman and Braun 1977, and others). Other possibilities are that males and females avoid each other or that members of the same sex are attracted to each other (de Vos 1983). The relative importance of any of these factors in determining the fall and winter sociality of grouse has received little attention, as winter studies are seldom undertaken and it is difficulty to identify different sex and age classes in the field. From 1979 through 1982, I studied Blue Grouse (Dendrugqus obscu-
Published in 1986.
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