Winter Use of Douglas-Fir Forests by Blue Grouse in Colorado

Abstract

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 (100200 yr old), and open ( 250 yr old) stands at elevations >300 m, but also used early successional stages (520 yr old) at elevations <300 m more than expected. Hines (1987) suggested that blue grouse use a broader range of conifer habitats in winter than previously reported. Zwickel and Bendell (1972) speculated that winter habitat and food probably did not limit populations because blue grouse disperse over a wide area of conifer forests in winter after leaving the breeding range, and winter food appears abundant. This hypothesis implies that blue grouse either use a wide range of available conifer habitats or a few specific conifer types that are widespread. For species such as the blue grouse that frequently occupy different seasonal habitats, knowledge of year-round habitat requirements is imperative for formulating sound management strategies. Schroeder (1984) identified a lack of quantitative information on winter habitat use. Accordingly, we investigated winter use of Douglas-fir forests by blue grouse in Colorado with the following objectives: (1) to compare use and availability among conifer stands to determine if preferential use was related to topography, species composition, and stand structure; (2) to compare tree species and diameter classes used with availability within stands; and (3) to compare habitats used by males and females. A. L. Cade, M. W. Crosby, J. J. Jeanson, and K. A. Medve provided field assistance. The manuscript benefited from reviews by A. E. Anderson, M. J. Armbruster, D. C. Bowden, C. E. Braun, R. C. Kufeld, R. T. Reynolds, R. A. Ryder, and D. F. Stauffer. Special thanks are extended to the many landowners who allowed us access to lands under their control. This is a contribution of the Colorado Division of Wildlife, Federal Aid to Wildlife Restoration Project