Richard W. Hoffman | USGS Science

USGS1993

Differential migration of Blue Grouse in Colorado

We examined migration of adult Blue Grouse ( Dendragapus obscurus ) in north-central Colorado by radio tracking 13 males and 19 females. Elevational changes associated with movements to winter areas were greater for males (median = 488 m, range = 183-671 m) than females (median = 122 m, range = -61-760 m). Males (median = 10.5 km, range = 1.0-29.4 km) also moved farther than females (median = 1.0 km, range = 0.1-28.0 km), resulting in partial segregation of sexes during winter. Directional orientation of movements to wintering areas was nonrandom for long-distance (>3 km) migrants. Median elevational change (122 m) and distance (0.6 km) between the first-winter and first-breeding areas for seven juvenile females were similar to movements of adult females. Males (median = 7 July) departed breeding areas earlier than females (median = 11 August), but arrived (median = 14 October) on winter areas about the same time as females (median = 23 October). Both sexes exhibited fidelity to winter areas. The average distance between winter locations ranged from 94 to 312 m (median = 135 m) for 11 radio-marked adults, suggesting Blue Grouse were sedentary on their winter ranges.

The Auk↗

USGS1990

Winter use of douglas-fir forests by Blue Grouse in Colorado

We studied winter use of Douglas-fir ( Pseudotsuga menziesii ) forests by blue grouse ( Dendragapus obscurus ) from 1981 to 1983 at 2 study areas in northcentral Colorado. Comparisons of used and available stands indicated grouse were concentrated spatially, but there were no consistent differences related to basal area of tree species, conifer stem densities, and topography that were common to both areas. Blue grouse used dense (2,000 stems/ha) second growth (40-75 yr old), open to dense (200-1,900 stems/ha) mature (100-200 yr old), and open (<100 stems/ha) old-growth (200-600 yr old) stands. Stands used were composed of Douglas-fir alone or in association with subalpine fir ( Abies lasiocarpa ), Engelmann spruce ( Picea engelmannii ), lodgepole pine ( Pinus contorta ), limber pine ( P. flexilis ), Rocky Mountain juniper ( Juniperus scopulorum ), and quaking aspen ( Populus tremuloides ). Grouse used stands on mesic northern and eastern aspects, on xeric southern and western aspects, at elevations of 2,530-2,960 m, and on slopes of 1-45°. Preferential use (P < 0.05) of Douglas-fir trees occurred within stands that had an abundance of limber pine (use = availability) and subalpine fir (use < availability). Large Douglas-fir (20-90 cm dbh) were preferred (P < 0.05) within stands that had an abundance of smaller (≤15 cm dbh) trees. Both sexes used similar trees.

Colorado↗