Survival and summer habitat selection of male greater sage-grouse (Centrocercus urophasianus) in southwestern Montana

Abstract

During the 20th century, Greater Sage-Grouse (Centrocercus urophasianus) populations in North America have declined by 69-99%. In southwest Montana little is known about the factors leading to declines in sage grouse populations; as a result, there are strong concerns regarding sage grouse population trends and habitat quality. I used radio-marked male sage grouse to obtain known-fate survival data and provide locations for habitat analyses. The objectives of the study were (1) to estimate survival rates of marked birds, and (2) to characterize the habitat used by sage grouse in southwestern Montana and compare it with available habitat. I used known-fate data to estimate annual survival, and I measured habitat attributes associated with aerial locations of instrumented sage grouse (use sites) and a series of randomly chosen locations within each study site (available sites).

From 2001-2005, 45 male sage grouse were instrumented and monitored. The estimated annual survival rate was 0.34 (95% CI: 0.21 to 0.47). In 2004 and 2005, I measured vegetation characteristics at 78 habitat plots (43 used, 35 available). I used logistic regression to model habitat selection; grass height was an important predictor of use, but the negative relationship between the probability of a site being used and grass height was opposite of what I had predicted. Further research is needed to determine whether this behavior is adaptive. An important predictor of use in my exploratory analysis was solar radiation index (SRI). The negative effect of SRI on habitat selection may have been a result of sampling only during summer daylight hours, and SRI may have acted as a proxy for microsite temperature. Further research is needed over a wide variety of conditions to determine how habitat components relate to or interact with each other, habitat selection by sage grouse, and survival of sage grouse.