Breeding ecology, survival rates, and causes of mortality of hunted and nonhunted greater sage-grouse in central Montana
Declines in productivity have been implicated in population declines for greater sage-grouse (Centrocercus urophasianus) in several areas, but there is considerable variation in reproductive effort, reproductive success and female survival, both temporally and spatially, and more data are needed. Despite declining populations, sage grouse are still legally harvested in most of their current range, including Montana, and uncertainty about how harvest impacts sage grouse vital rates remains. The reproductive activity, survival rates, and causes of mortality of hunted and nonhunted sage grouse females were monitored year round using radio-telemetry in central Montana during 2004 and 2005. Data on nest survival and brood survival were also collected. Nest survival was greater for renests, 0.56, than for first nests, 0.32. Brood survival to 30 days posthatch was estimated as 0.79. Reproductive effort and reproductive success were higher in 2005. Female survival during the nesting season was constant, 0.94 monthly.Female survival during July of both years was similar on both sites, 0.99 to nearly 1.00, but survival was lower during August and declined between 2004 and 2005 from 0.94 to 0.84 on the hunted site and declined from 0.98 to 0.94 on the nonhunted site. This decline in survival between years in August was likely due to West Nile virus, as it was first detected in sage grouse in this area in August 2005. Female survival during the hunting season was lower for females that spent more days brood-rearing than those that spent few or no days brood rearing, and females on the hunted site had lower survival than females on the nonhunted site. However, lower survival rates on the hunted site could not be attributed to hunter kill, because no radio-marked females were bagged or reported by hunters and no evidence of hunter kill was observed. During the hunting season, monthly survival estimates ranged from 0.87 for hunted-site females that invested heavily in brood rearing to 0.99 for nonhunted-site females that invested little or no time in brood rearing. Overwinter survival was different between years, and monthly survival during winter 2004-05 was estimated as 0.98 and as 0.97 during winter 2005-06.