OOS 2-8
Long-term trends in sage-grouse demography and habitats on the Sheldon -Hart Mountain National Wildlife Refuge complex and adjacent BLM lands: An opportunity to assess impacts of feral horses and regional habitat connectivity
Greater Sage-grouse populations are declining. Grazing by feral horses and livestock have been hypothesized to contribute to declines because of the impacts on vegetation. The effects of grazing by feral horses or livestock on Sage-grouse in the Great Basin are poorly understood, however, because livestock and feral horses often occur together. We are investigating the effects of feral horse grazing on Sage-Grouse demographic parameters in Northern Nevada and Southern Oregon using a historic and contemporary dataset. We surveyed Hart Mountain National Wildlife Refuge, Sheldon National Wildlife Refuge, and Vya-Massacre Rim WSA area to evaluate different levels of grazing. These study sites allowed for isolation of feral horse grazing and domestic cattle. The three levels of grazing include no grazing, grazing by feral horses only, and grazing by feral horses and cattle combined. We captured Sage-grouse during the spring leking period. Males are marked with field readable leg bands and females are radio collared. Using telemetry, we monitored nesting, brood rearing and survival of adult females and evaluated annual survival of males using mark recapture techniques.
Results/Conclusions
We monitored 84 nests across the three sites during the 2013 season. Daily survival rate varied among sites and with hen age (adult or yearling) in our top model. Nest period survival, calculated from the top model, in the absence of grazing was highest at 38.2% (95% CI 19.9, 56.3) while nest period survival on the other two sites with grazing, were similar with 11.5% (95% CI 3.4, 25.2) with feral horse grazing only, and 9.5% (95% CI 1.9, 24.8) with livestock and feral horse grazing combined. Our results suggest that grazing by feral horses and livestock may influence nesting success of Sage-grouse.