Migratory Birds, Intermountain West Joint Venture, Region 6
Water scarcity in semiarid environments provides an ideal system to evaluate the role of water-rich mesic habitats in structuring the distribution and abundance of wildlife. We used remote sensing and point process analyses to evaluate how spatiotemporal variability in scarce sage-grouse (Centrocercus urophasianus) summer habitat controls overall sage-grouse distributions in Oregon, California, and northwestern Nevada, from 1984–2011. Spatial patterns in sage-grouse population density were linked to changes in summer habitat availability over time, space, and land tenure. Despite encompassing 80 percent of breeding populations clustering within 10 km of these mesic sites. Wet years likely contribute to pulses in recruitment that are evident in sage-grouse population cycles. In wet years, sparse populations are gathered closer to summer habitats (5.5 km) than dense populations are in dry years (6.1 km), reducing a habitat constraint that limits recruitment. In dry years, reliability of succulent vegetation in wet meadows and other irrigated agricultural lands likely maintains populations when recruitment is low. Natural, unirrigated, summer habitats are equally proximal to populations in dry years, suggesting that long-lived females maximize fitness by anticipating wet years. In wet years, more abundant natural summer habitats were twice as close to sage-grouse populations than irrigated agricultural sites, providing conditions for abundant food resources and increased populations. Private ownership of 81 percent of all mesic resources inextricably links sage-grouse conservation to ranching in the West. A holistic conservation strategy inclusive of private lands through voluntary and incentive-based approaches may reduce conversion of summer habitats to non-compatible land uses.
The study has been completed across >32 million acres of sage-grouse range (dark gray) in the westernmost portions of their distribution. Funding has been secured to expand the study rangewide (>145 million acres; light gray). Efforts to complete rangewide work are underway.