Anthropogenic and Natural Determinants of the Population of a Sensitive Species: Sage Grouse in Nevada

This paper uses Nevada data to conduct regression analyses of the relationship between sage grouse (Centrocercus urophasianus) population sizes and potential causal factors. This is policy-relevant because of current petitions for listing this species under the Endangered Species Act. A key feature is that, although monitoring of sage grouse has occurred for many decades, data collection methods and level of monitoring effort have not been consistent. To account for this feature we use, as dependent variables, standardized measures such as population counts and harvest (hunting success) per unit of effort. Preliminary findings suggest that such measures have been particularly sensitive to whether or not humans used strychnine for predator control, with normalized measures of grouse populations higher in years when strychnine was employed. Our results also suggest a positive association between the number of cattle on the range and normalized measures of grouse population. This is a controversial finding as some studies suggest a negative impact of cattle grazing on grouse. Our data do not include indications of the timing and precise nature of grazing practices and so should be interpreted with caution.