Post-Nesting Movements of Female Blue Grouse

Abstract

Four radio-marked adult female blue grouse, Dendragapus obscurus, had brood ranges 1 km to more open brood ranges. Cumulative movements of 7 of 20 brood hens exceeded 1 km in the first week post-hatch; two adults remained within 0.5 km of their nests but five yearlings moved beyond that. Mean daily movements of brood hens in the first week post-hatch were 0.14 and 0.11 km/day for yearling and adult females, respectively. Mean bimonthly sizes of home ranges of brood hens were relatively constant throughout summer but mean cumulative sizes increased steadily. Eleven of 30 hens moved 1 to 3.2 km from their nest sites immediately after losing their clutches or broods; 10 entered dense forest. Post-nesting home ranges of 12 of 28 broodless hens were >0.5 km from their nests. Mean sizes of pre-migratory bimonthly home ranges of most broodless females remained constant following loss of eggs or chicks and were the same size as those of brood hens; mean cumulative sizes increased steadily until departure from breeding range. Hens with broods used more open vegetative cover than those without broods and remained on breeding range until late August or early September. Hens without broods remained on breeding range from 3-54 days after loss of nests or chicks and, on average, left breeding range about one month before hens with broods. Movements of brood and broodless hens from breeding range (postbreeding migration) were largely unidirectional and began with a sudden move toward upland forest. Migratory movements ranged from 1-1.8 km/day. We suggest that: 1) some yearling females may nest in sub-optimal habitats that not adjacent to acceptable brood ranges because of saturation of optimal habitats by adults and other yearlings, and 2) that broods may remain on breeding ranges longer than broodless females because of resources required by chicks. Hannon et al. (1982) provided evidence that most yearling female blue grouse, Dendragapus obscurus, settle for nesting only after most adults laying or incubating eggs. They suggested that restriction of movements by nesting adult females tends to reduce interactions between the two age-classes and might explain settling patterns among yearling females. We studied post-nesting movements of radio-marked female D. obscurus with and without broods to examine the relationship between preand post-nesting home ranges. The principal question we asked was: are sites settled by females in spring chosen to provide brood range for chicks? This question bears on a suggestion of Sopuck (1979) that adults may be excluding some yearlings from prime nesting habitat. Secondary objectives were to compare post-nesting movements, post-nesting use of cover, and migration from breeding range of brood hens to those of broodless hens, for these comparisons might provide clues as to needs of hens with chicks. Studies were conducted in the springs and summers of 1976 and 1977 in the foothills and nearby mountains of east-central Vancouver Island, British Columbia.