PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 156, Spring 2009: Ecological Consequences of Climate Change




  

Climate Change and Bird Distributions

What Kind of Future Will Birds Face?

Claire Peaslee with Diana Stralberg


 
Introduction
CEO's Column
Fingerprints of Climate Change
Projecting Birds' Future
Song Sparrows and Climate
PRBO's Climate Change Initiative
Climate Modeling
Planned Giving
Focus on a Home Patch
PRBO Highlights
 


Red-breasted Nuthatch. Photo by Tom Grey.
When you walk in the forests of California's Sierra Nevada range, you may be delighted to hear and see Fox Sparrows, Black-throated Gray Warblers, and Red-breasted Nuthatches. But it's doubtful that you'd be surprised by their presence there. We often link our chances of encountering birds to particular places—the region, vegetation, elevation, and so forth. To see a Blue Grosbeak, go to the edges of riparian forests in the Central Valley—and you will usually find Tree Swallows and Black-headed Grosbeaks, too. For Ash-throated Flycatchers, walk among California's oak woodlands, where Oak Titmice and Acorn Woodpeckers are almost certain to be.

Today, though, a new uncertainty permeates traditional wisdom about birds—and also our outlook on conservation. How will the changing climate affect where birds can live? Ruptured ecological links and poleward shifts in birds' ranges have already been documented.

How do we protect bird species today, when they may occur in very different places tomorrow? Dr. John Wiens, Chief Conservation Science Officer at PRBO, explains: "New scientific tools and new ways of thinking will be needed in order to understand how fast and how far birds might move in response to climate change. Future conditions for birds and other organisms will likely be entirely different from anything we've experienced and studied up to the present."
Acorn Woodpecker. Photo by Tom Grey.

Developing scientific tools to help conservation look forward is a priority of current research at PRBO. Whereas birders accumulate knowledge, through experience, of birds' whereabouts, scientists analyze large quantities of data collected in the field to acquire quantitative knowledge. Results can take the form of distribution maps showing where and how often certain birds might occur across a given region (Observer 155, winter 2009).

In a new PRBO study, the region is also large: California. Diana Stralberg, a landscape ecologist at PRBO, says, "Because of its great size and topographic complexity, California supports exceptional biodiversity, but ecosystems here are subject to large-scale stresses due to a rapidly growing human population and changing climate. To maximize biodiversity, now and in the future, people need to know where conservation and restoration activities should be prioritized throughout the state. These are questions that our scientific efforts address."

A PRBO team that Diana headed, with Dennis Jongsomjit and Chrissy Howell, developed models of bird distributions across California incorporating data on the changing climate. The huge amounts of data used in this analysis came primarily from PRBO. Our partners at Klamath Bird Observatory (KBO), the U.S. Forest Service's Redwood Sciences Lab, and the USGS Breeding Bird Survey also provided data. Says John Alexander, of KBO, "By sharing data and resources, we better serve bird conservation and demonstrate that the whole is greater than the sum of its parts."
Tree Swallow. Photo by Peter LaTourrette.

The results project what's in store for birds in the next 50 to 100 years. Selected for this study were 60 bird species that inhabit oak woodland, grassland, scrub chaparral, conifer forest, and riparian (streamside) forest. Maps showing where these birds are likely to occur in the future are available at the California Avian Data Center, a powerful new online resource created by PRBO (that you can use; visit www.prbo.org/cadc).

The models help identify which species are likeliest to shift their distributions in California as their habitats come under growing stress related to climate change. For example, coniferous forest birds like the Fox Sparrow may move to higher elevations. Ash-throated Flycatcher may expand its range in California, as its scrub and oak woodland habitat spreads.

While some climate-change winners appear in the models, a majority of species are projected to decrease. And a closer look at some of the "winners," like the Ash-throated Flycatcher, suggests that potential gains in habitat due to climate change may be cancelled out by expanding urban and exurban development.
Ash-throated Flycatcher. Photo by Tom Grey.

These analyses incorporate regional climate models that project how seasonal temperatures and rainfall patterns are likely to shift geographically as a function of greenhouse gas increases in the atmosphere.

Diana Stralberg comments on the findings: "We see many species significantly shifting their California distributions—often coastward or to higher elevations (though we were also surprised by the variability in species' responses)." Certain regions in California stand out as "hot spots" of change, where significant loss or gain in avian diversity is likely. Some of the greatest increases in bird diversity are foreseen for higher elevations of the Sierra Nevada and other mountain ranges and for the North Coast region. These are areas where natural resource protection promises to pay great dividends in the future.

The power of data

Even before this campaign to understand the future of birds took shape, PRBO had a powerful resource to deploy—data. Over recent decades we have been part of a monumental effort to survey birds across much of California. The original intent was to help guide management and restoration efforts, generally ones with fairly short time spans. When field biologists were gathering all that information, nobody really foresaw its importance today for modeling changes in bird distribution.

"This is a great example of why PRBO's ‘eyes-on-the-ground' biology is worth the investment of effort," observes Tom Gardali, Associate Director of the Terrestrial Ecology Division. "We originally set out to use locally collected data to inform managers in their specific efforts to increase numbers of birds. Now these same data enable us to view the future and address conservation challenges that come with climate change."

As this wealth of data is put to new uses, new concerns come to light. For example, some California birds that shift geographically may find themselves in all-new species associations, because climate change may not affect every member of a present-day bird community the same way. What might be the consequences for conservation?

As PRBO scientists and our research partners bring forth telling new projections of changes likely to affect bird distribution, predictive modeling will help to shape and guide innovative management strategies. Conservation, like wildlife, will need to be adaptable in an uncertain future.

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