Conservation of priority birds in sagebrush ecosystems
This article is part of a larger document. View the larger document here.Abstract
Sagebrush ecosystems occupy over 62,000,000 ha of the western US. However, they have been degraded or completely eliminated by agricultural conversion, overgrazing by domestic livestock, invasion of exotic plants, expansion of pinyon and juniper woodlands, uncharacteristic wildfires, and fragmentation. This habitat loss has led to an increasing number of special status species, including 630 plant and animal species of conservation concern. In this paper, we focus on the 22 taxa of sagebrush associated birds that are priorities in Partners in Flight Bird Conservation Plans. These range from sagebrush obligates-Greater Sage-grouse (Centrocercus urophasianus), Gunnison Sage-grouse (C. minimus), Sage Thrasher (Oreoscoptes montanus), Sage Sparrow (Amphispiza belli), Brewer's Sparrow (Spizella breweri)-to grassland associates such as Short-eared Owl (Asio flammeus) and Vesper Sparrow (Pooecetes gramineus). Partners in Flight has identified five of these species for the continental Watch List-Swainson's hawk (Buteo swainsoni), both sage-grouse, the Short-eared Owl, and Brewer's Sparrow-which places them among the highest priority species for conservation action in North America. We also examine the extent to which sage grouse may serve as classic umbrella species for shrubsteppe avifauna. These species tended to occur together-83 pairwise correlations of relative abundance were significant (8.55 expected). Factor analysis of these data showed that species formed groups based on habitat associations much as expected, although sage-grouse aligned more closely with the Vesper Sparrow than expected. Population trends for three major physiographic strata that encompass sagebrush ecosystems-the Columbia Plateau, Wyoming Basin, and Basin and Range-showed the Columbia Plateau to have many more declining population trends. Habitat associations for declining species included both sagebrush and grassland types. Historic (1850) and current population sizes were estimated for 12 priority taxa in the Interior Columbia Basin based on predicted areas of historic and current source habitat. Estimated current population sizes are, not surprisingly, drastically reduced from historic numbers. The Western Meadowlark (Sturnella neglecta) showed the least percent reduction and Grasshopper Sparrow the most. For six species that had significant or near significant declines in the Columbia Plateau since 1966 and for which we had historic and current habitat estimates, the estimated historical declines were all remarkably similar to recent trends. Trends and management activities on public lands in Idaho, Oregon, and Washington that may be contributing to disproportionate declines in priority birds include an increase in the area burned annually by wildfire, an increase in the biomass of grazing cattle, and continued fencing and water development that spread negative impacts over an ever greater portion of the landscape. We suggest that conservation of sage-grouse populations in reasonable numbers well distributed across their historical ranges also will provide substantial benefits for many, or even most, other bird species that co-occur with these grouse. Given that more than 57 percent of this habitat is in public ownership and that concern for the future of sage-grouse continues to build, we have all the information and opportunity we need to take action. Indeed, if we cannot successfully conserve sage-grouse and the sagebrush ecosystem in the US given our theory, our knowledge, and our large blocks of public land, then one wonders how we can succeed for other species elsewhere.