Some Birds and Reptiles Vulnerable to Climate Change in the Southwestern United States

Reston, Virginia - With temperatures projected to increase approximately 6 degrees Fahrenheit in the Southwestern United States and precipitation projected to decrease between 5 and 20 percent this century, habitat for some bird and reptile species may be negatively affected, according to new research by scientists from the U.S. Geological Survey, University of New Mexico and Northern Arizona University.

“This study identified better tools and strategies to conserve and sustain wildlife habitats in the Western U.S. using specific information about climate change consequences from models the authors developed,” said Dr. Charles van Riper III, senior research ecologist with the USGS and report co-author. “In conducting this study, we coupled existing global climate change models with newly developed species distribution models to estimate future losses and gains of Southwestern bird and reptile species.”

“Resource managers need scientific products and tools to inform planning and decisions under climate change and habitat alteration,” said Dr. Stephen Jackson, director of the Department of the Interior’s Southwest Climate Science Center. “This study will help managers assess the potential consequences of climate change for bird and reptile species, identify vulnerable species and populations and develop robust plans for climate adaptation.”

Fifteen species of birds and 16 reptile species comprised the study, including well-known species such as the Gila monster, horned lizard, chuckwalla, Sonoran desert tortoise, pinyon jay, pygmy nuthatch, sage thrasher and black-throated sparrow.

Projected changes in bird and reptile ranges varied widely among species:

- One-third of the ranges are predicted to expand, while two-thirds are predicted to contract.

- Several reptile species are projected to lose between 25 and 72 percent of their range, including the Gila spotted whiptail, Arizona black rattlesnake and ornate box turtle.

- Numerous bird species are projected to lose between 78 and 85 percent of their range, including Williamson’s sapsucker, sage thrasher, red-naped sapsucker and pygmy nuthatch.

An important finding by the authors was bird or reptile species that currently occupy warmer locations in any season may experience range gains, whereas species that currently occupy wetter spring or summer locations may experience range contractions.

Another key finding by the authors was that the more fragmented bird and reptile ranges are under today’s conditions, the more vulnerable they appear to the future effects of climate change. The more fragmented a species’ current range, the greater the magnitude of possible future decline.

“Proactive land management actions that enhance landscape connectivity and conserve core areas might lessen the severity of range contractions projected over the coming century for birds and reptiles,” said James Hatten, lead author and research biogeographer with the USGS. “Land management actions that reduce the distance between habitat patches, increase connectivity, and enlarge core areas could be helpful for bird and reptile species across the landscape.”

Numerous studies have examined the vulnerabilities of wildlife to climate change without considering coexistence of plants and wildlife. After plants were incorporated into their models, future predictions for birds and reptiles became even more severe.

When the authors modeled the assumption that reptiles will not be able to disperse fast enough to escape a shifting climate (think of animals with tiny or no legs), all their future ranges contracted. When the authors assumed reptiles can disperse as fast as the climate shifts, such as birds, over half of reptile species’ ranges expanded, but the authors think this is highly unlikely given the life histories of many reptiles. In contrast, several desert-scrub bird species (black-throated sparrow, gray vireo and sage sparrow) are projected to increase their future ranges by over 30 percent.

Additional quotes from the study authors and partners:

Dr. Kenneth Cole, a research professor at Northern Arizona University and report co-author.

“Projected range shifts of plant species in relation to birds and reptiles that rely on them are important for understanding how mutualistic relationships may alter the overall vulnerability of these animal species. The reliance of birds and reptiles on specific plant species may limit their migration and dispersal abilities in the Southwestern United States over the next century due to slow migration rates of certain plant species. This lag effect highlights the importance of plants in conservation planning for animal species that rely closely on specific plants for some aspect of their life or natural histories, for example, food, hunting and breeding.”

Lisa Thomas, National Park Service program manager for the Southern Colorado Plateau Network.

“Climate-related biodiversity disruption is likely to be a central theme of natural areas stewardship in the 21st century. By using an integrated modeling approach, the authors were able to evaluate exposure and sensitivity for a range of bird and reptile species to predicted climate change. When combined with long-term species observations, such as those produced by National Park Service Vital Signs Monitoring, this model-based study will provide an exciting opportunity to compare hypothesized trends in species distribution to field-based observations.”

Dave Krueper, migratory bird biologist with U.S. Fish and Wildlife Service.

"This report will be of great value to land managers and to the US Fish & Wildlife Service as we prepare to manage for a changing natural world in the Southwest. Of particular value to our program are the predictive distribution maps for 15 avian species, nine of which were already identified as being of potentially high concern based on limited range and identified conservation threats. Predictive modeling will help us identify avian populations and the distributions which are particularly vulnerable to habitat change, which will allow us to apply limited resources toward conservation efforts for their benefit.”

Ginny Seamster, BISON-M/Share with Wildlife Coordinator of New Mexico Department of Game and Fish

“The authors’ inclusion of shifting plant distributions in their modeling efforts, as well as development of detailed conceptual models that consider numerous aspects of species biology and ecology, is an interesting and valuable addition to traditional methods for evaluating the effects of climate change on species geographic distributions. Results from this study help to fill information gaps regarding environmental change effects for many species and I anticipate that they will inform multiple species accounts in the New Mexico Department of Game and Fish’s publically accessible species database, the Biota Information System of New Mexico (bison-m.org).”

The study was a partnership of the USGS, Northern Arizona University and University of New Mexico. The work was supported by the DOI Southwest Climate Science Center, which is managed by the USGS National Climate Change and Wildlife Science Center. The center is one of eight that provides scientific information to help natural resource managers respond effectively to climate change.

The report, Identifying Bird and Reptile Vulnerabilities to Climate Change in the Southwestern United States, is authored by James Hatten, USGS; J. Tom Giermakowski, University of New Mexico; Jennifer A. Holmes, Erika M. Nowak, Matthew J. Johnson, Michael Peters, and Charles Truettner, Northern Arizona University; Kirsten E. Ironside, Charles van Riper III, andKenneth L. Cole, USGS.