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Contact: Catherine Puckett
United States Geological Survey

Southwestern bird and reptile distributions to shift as climate changes

A few winners, but many more losers

Dramatic distribution losses and a few major distribution gains are forecasted for southwestern bird and reptile species as the climate changes, according to just-published research by scientists with the U.S. Geological Survey, the University of New Mexico, and Northern Arizona University.

Overall, the study forecasted species distribution losses - that is, where species are able to live - of nearly half for all but one of the 5 reptile species they examined, including for the iconic chuckwalla. The threatened Sonoran (Morafka's) desert tortoise, however, is projected to experience little to no habitat losses from climate change.

Breeding bird ranges exhibited greater expansions and contractions than did reptile species. For example, black-throated sparrows and gray vireos are projected to experience major gains in breeding habitat, but pygmy nuthatches, sage thrashers and Williamson sapsuckers are forecasted to experience large losses in breeding habitat, in some cases by as much as 80 percent. Thus, these three species might be expected to experience large future population declines.

The iconic pinyon jay is expected to experience from one-fourth to one-third loss in breeding habitat in the future, as its welfare is tied to declining pinyon pine habitat.

"Not surprisingly, whether a species is projected to be a winner or a loser depends primarily on its natural history and habitat needs and requirements," said USGS scientist Charles van Riper III, the lead author on the study. "Land managers should be aware of these potential changes so that they can adjust their management practices accordingly."

To conduct the study, scientists coupled existing global climate change models with newly developed species distribution models to estimate future losses and gains of 7 southwestern upland bird species and 5 reptile species. The study area focused on the Sonoran Desert and Colorado Plateau ecosystems within Arizona, western New Mexico, Utah, southwestern Colorado and southeastern California, but also included the rest of the Western United States. Focal wildlife species included resident and migratory birds and reptiles, which make up most of the vertebrate biodiversity in the region.

Temperatures in this region are projected to increase 6.3-7.2 F (3.5-4°C) within the next 60-90 years while precipitation is projected to decline by 5-20 percent.

"Changes of this magnitude may have profound effects on distribution and viability of many species," noted Stephen T. Jackson, director of the Interior Department's Southwest Climate Science Center. "Temperature matters a lot, biologically, in arid and semi-arid regions."

One very practical result of the project is a website with a series of range maps projecting the potential effects of climate change on bird and reptile distributions in the Western United States for three different time periods in the next 90 years. These predictions can help managers and policy makers better prioritize conservation effects, van Riper said.

"Wildlife resource managers need regionally specific information about climate change consequences so they better identify tools and strategies to conserve and sustain habitats in their region," said Doug Beard, director of the USGS National Climate Change and Wildlife Science Center that supported the project. "Managers can use these results to help plan for ways to offset projected effects of climate change on these species."

Detailed Bird Species Projections:

Overall: Black-throated sparrow and gray vireo are projected to experience major gains in breeding habitat. In contrast, pygmy nuthatches, sage thrashers and Williamson sapsuckers are projected to experience large losses in breeding habitat. Thus, these three species might be expected to experience large future population declines.


Overall: Future climate change will negatively affect the distributions of reptiles in the Western and Southwestern U.S. The one exception is the Sonoran desert tortoise, which is forecasted to expand, and, if a decrease happens, only by about one percent.

Reptiles can't move as easily as birds nor can they regulate their body temperature, so they can only move minimally in response to changing climates. The authors found that the greater the projected distributional gain or loss in a reptile species was directly tied to the warmth of its current range. Thus, the less mobile reptiles will be more greatly affected by increasing temperatures.


The report, Projecting climate effects on birds and reptiles of the southwestern United States, is authored by Charles van Riper III, USGS; James Hatten, USGS; J. Tom Giermakowski, University of New Mexico, Jennifer A. Holmes and Matthew J. Johnson, Northern Arizona University, and others.

For more information on the USGS National Climate Change and Wildlife Science Center, please visit its website at https://nccwsc.usgs.gov/.

USGS provides science for a changing world. Visit USGS.gov, and follow us on Twitter @USGS and our other social media channels.

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