SAGE-GROUSE AND THE HUMAN FOOTPRINT: IMPLICATIONS FOR CONSERVATION OF SMALL AND DECLINING POPULATIONS

Implementing conservation in the face of unprecedented landscape change requires an understanding of processes and scales that limit wildlife populations. We assessed landscape-level processes influencing sage-grouse (Centrocercus urophasianus), to a migratory population in the Milk River Basin (MRB), northeast Montana, USA, and south-central Saskatchewan, Canada. A regional analysis of leks (e.g., communal breeding sites) documented that populations impacted by the increasing extent of agricultural tillage, roads, and energy development out to spatial scales larger than previously known. Using bird abundance as a novel way to evaluate human impacts revealed relationships that would have been missed had we not incorporated lek size into analyses. For example, large leks are 4.5 times less likely to occur than small leks when agricultural tillage fragments 21% of land within 1.0km of breeding sites. Sage-grouse in the MRB met or exceeded demographic rates of stable or increasing populations, and thus, are not likely the cause for annual declines. Spring and summer survival of radio-marked females was higher in 2008 (0.91), than in 2007 (0.55), the year we documented an outbreak of West Nile virus. Nest sites in the MRB had lower shrub cover (15%) than range-wide estimates (15-56%), and overall shrub cover instead of sagebrush cover, was a better predictor of nest-site selection. Plains silver sagebrush (Artemesia cana cana) made up half of total shrub cover (7.1%) at nest sites, suggesting that other shrubs compensate for lower sagebrush densities in the MRB. We discovered the longest migratory event observed for sage-grouse, with females travelling 40km to120km from breeding to wintering areas in Wyoming big sagebrush (A. tridentata wyomingensis) habitats in Montana. Habitat may be sufficient to maintain a small population in the MRB, but its ability to persist through time and to buffer against stochasticity is depressed now that this once-large population has become small and isolated. For example, impacts of disease are compounded when acting on fewer individuals and working synergistically with fluctuations in growth rates. Consequently, conservation of sage-grouse in the MRB will depend on maintaining the current habitat base, and on restoring sagebrush-dominated grasslands currently occupied by agricultural tillage.

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