Climate change impacts reptiles and birds in the southwest

Arizona Black Rattlesnake, Crotalus cerberus

Awareness and acceptance of climate change is slowly spreading  in American society. In a report released by the USGS’ Department of the Interior reports the results of modeling current and  future breeding ranges of seven bird and five reptile species in the Southwestern United States with sets of landscape, biotic (plant), and climatic global circulation model (GCM) variables. Charles van Ripper and colleagues (2014) considered climatic, landscape, and plant variables to developing and testing probabilistic models. Climatic variables included the maximum and minimum mean monthly and seasonal temperature as well as precipitation for three time periods. Landscape features included terrain ruggedness and insolation. They also considered plant species distributions as candidate explanatory variables where prior ecological knowledge implicated a strong association between a plant and animal species.

Projected changes in range varied widely among species, from major losses to major gains. Breeding bird ranges exhibited greater expansions and contractions than did reptile species. The authors projected range losses for Williamson’s sapsucker and pygmy nuthatch of a magnitude that could move these two species close to extinction within the next century. Although both species currently have a relatively limited distribution, they can be locally common, and neither are presently considered candidates for prospective endangerment. Breeding bird ranges exhibited greater expansions and contractions than did reptile species.

The authors also project range losses of over 40 percent, from its current extent of occurrence, for the plateau striped whiptail, Arizona black rattlesnake, and common lesser earless lizard. Currently, these reptile species are thought to be common or at least locally abundant throughout their ranges.  The total contribution of plants in each distribution model was very small, but models that contained at least one plant always outperformed models with only physical variables (climatic or landscape). The magnitude of change in projected range increased further into the future, especially when a plant was in the model.

Bird species with the strongest association to a landscape feature during the breeding season, such as terrain ruggedness and insolation, exhibited the smallest contractions in projected breeding range in the future. In contrast, bird species that had weak associations with landscape features, but strong climatic associations, suffered the greatest breeding range contractions. Thus, landscape effects appeared to buffer some of the negative effects of climate change for some species.

The magnitude of change in projected bird  breeding range was positively related to the annual average temperature of their baseline distribution, thus species with the warmest breeding ranges exhibited the greatest changes in future breeding ranges. This pattern was not evident for reptiles, but might exist if additional species were included in the model.

The results provide managers with a series of projected range maps that will enable scientists, concerned citizens, and wildlife managers to identify what the potential effects of climate change will be on bird and reptile distributions in the Western United States. The authors  hope that the results can be used in proactive ways to mitigate some of the potential effects of climate change on selected species.

The entire document is available on-line.

Charles van Riper III, James R. Hatten, J. Tom Giermakowski, David Mattson, Jennifer A. Holmes, Matthew J. Johnson, Erika M. Nowak, Kirsten Ironside, Michael Peters, Paul Heinrich, K. L. Cole, C. Truettner, and Cecil R. Schwalbe 2014. Projecting Climate Effects on Birds and Reptiles of the Southwestern United States. Open-File Report 2014-1050, U.S. Department of the Interior, U.S. Geological Survey. 100 pp

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