Recruitment and juvenile survivorship may be primary factors affecting blue grouse Dendragapus obscurus populations. Studies of blue grouse relationships with weather revealed contrasting effects of winter and spring precipitation on populations, and the subsequent need for a better understanding of weather effects on the species. The relationships between winter, spring, and summer weather, and percent immature blue grouse in fall harvest were ascertained to understand potential effects of weather on blue grouse brood recruitment and survivorship. These data were based on 15 years of hunter-harvested grouse wing data obtained from the Oregon Department of Fish and Wildlife in Wallowa County. Fall immature:adult ratios were positively related to monthly mean minimum temperature (P = 0.04) and negatively related to precipitation (P = 0.05) during the breeding period (March-April) (r? = 0.49). The relationship with monthly mean minimum temperature also was present during May (P = 0.03, r? = 0.30), but no relationship existed with precipitation during this time period; weather conditions during April alone were not related to fall immature:adult ratios. Relationships were not detected between population age-ratios and weather during winter (December-February), peak hatch (four weeks centered on peak hatch date), post-hatch (June), summer (July-August), or during any other months. Weather likely affected hen condition and subsequent ability to care for juvenile grouse. It also may have affected food or cover available to juvenile grouse, as well as ability to thermoregulate. Weather likely affects grouse differently in different climatological regions. Increased understanding of weather effects on specific populations may enhance management efforts for grouse.
Key words: age ratios, blue grouse, brood recruitment, Dendragapus obscurus, Oregon, survivorship, weather effects
Eric C. Pelren & John A. Crawford, Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331, USA