The Dusky Grouse (until recently known as the Blue Grouse) is the largest of Montana's three species of mountain grouse. Both sexes have long, square tails which are unbarred. Males have slate-colored upper parts, white-based neck feathers around the air sacs, and yellow-orange eye combs. Females tend to be browner than males and have barring on the head, neck, and back. Both sexes have uniform blue-gray breasts and bellies, and feathered legs. Adult males range from 18.5 to 22.5 inches in length and 2.5 to 3 pounds in weight; adult females range from 17 to 19 inches in length and average about 2 pounds in weight.
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
Dusky Grouse are most likely to be confused with Spruce (Franklin) Grouse in Montana. Male Spruce Grouse, however, are considerably smaller than male Dusky Grouse and have a black breast patch. Female Spruce Grouse have white under parts with conspicuous black barring, while female Dusky Grouse are bluish-gray beneath.
Dusky Grouse winter at high elevations in conifer stands. In early spring, they descend to lower altitudes, where they prefer forest edges and openings. Broods may be found quite far from timber during summer and early fall. In the Bridger Mountains in early summer, broods were often observed in grass-forb areas (with arrow-leaf balsamroot being dominant); increased use of deciduous thickets was observed in late July to August (Mussehl 1958). See also Martinka 1970 for habitat comments from the Sapphire Mountains.
In winter they eat mainly conifer needles. In summer they eat a mixed diet of insects, green plants and berries. The young eat mainly insects (Mussehl 1971).
Brood movement in summer is generally less than 0.5 mile. Brood break-up appeared concurrent with fall dispersal, in late August to early September and had lateral and altitudinal components. Brood range densities were 27 (1957) and 34 (1958) in a 1 square mile area (Mussehl 1958).
Hatching dates in the Bridger Mountains ranged from May 25 to July 11, with the peak the 3rd week of June (Mussehl 1958). Near Fortine, hatching dates were June 10 to August 15; broods ranged from 1 to 10 young.