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Technical Report

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The Lower Colorado River and Rio Grande Basins are home to many riparian vertebrate species with different degrees of rarity. In our study, we focused on two species of birds and two species of gartersnakes that are associated with riparian areas: the Yellow-breasted Chat (Icteria virens), the Yellow Warbler (Setophaga petechia), the Northern Mexican Gartersnake (Thamnophis eques megalops) and the Narrow-headed Gartersnake (T. rufipunctatus). While the extent of distributions of these species is relatively large, they are often patchily distributed in populations that are small; in addition, both gartersnake species are listed as threatened under the Endangered Species Act. Aside from detrimental effects of direct habitat loss and degradation throughout the southwestern United States, future changes in water availability might threaten the long-term persistence of populations of any one of these species. To evaluate this vulnerability at a landscape scale, we built species distribution models under current and future projected climates for each species. For modeling, we relied on climatic and hydrological predictions (downscaled CMIP3 climate and hydrology projections) developed by the Bureau of Reclamation and its partners as part of the West-Wide Climate Risk Assessments within the WATERSmart initiative. We also relied on NASAs Moderate-Resolution Imaging Spectroradiometer (MODIS) to derive a spatially explicit index that quantifies riparian vegetation in space and time. Using downscaled climate projections and other landscape data, we were able to project these riparian vegetation metric forward in time. The projected changes in water availability by end of the century will directly affect the availability of permanent water and riparian vegetation creating the habitats of our study species. Our results suggest significant and negative changes in future landscape suitability for all species (up to 64% loss of suitable area), which are in addition to already identified threats facing these species. Best models included the index of riparian vegetation (linked to water availability) as an important component of the predictions, but we also note that finer scale examination of hydrology and climate effects on habitats would be much more useful for effective management.'



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