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January / February 2005 Cover

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A Bird's-Eye View of Climate Change


A Bird's-Eye View of Climate Change
Computer modeling predicts dramatic shifts in species' ranges

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Chickadees, song sparrows, robins and other common bird species are among the familiar sights and sounds of Maine and much of the eastern United States, but in a world affected by a changing climate, they may not always be around.

"Both climate and landscape are important to birds," says Steve Matthews, who, for his master's degree in wildlife ecology at the University of Maine, studied how bird species might respond to a warmer world.

Matthews worked with UMaine Professor Raymond O'Connor on a computer model using current information about climate and the eastern U.S. landscape to show where bird species occur. Bird density is hard to measure directly; the researchers used incidence, a measure of how reliably a species can be found at a location.

O'Connor's research focuses on the consequences of changing landscapes and agricultural practices on birds and other wildlife in Great Britain and North America.

Using current data about climate, vegetation and elevation, the researchers found that their model faithfully reproduced the known ranges of 150 bird species. But the model wasn't perfect, says Matthews, a native of Charlottesville, Va. For most of 36 other species, the model did a poor job of reflecting current knowledge. Nevertheless, success with a large number of species meant the computer model had accurately captured factors critical to those species.

Matthews and O'Connor then turned to the future. One of the aces in their hand was a recent study of how eastern forests might change in a world made warmer by increasing greenhouse gases in the atmosphere. That work by two U.S. Forest Service scientists, Louis Iverson and Anantha Prasad of the Northeastern Research Station, paved the way for Matthews and O'Connor to look at the consequences for birds.

Breed Bird Survey Map
North American Breeding Bird Survey map of current distribution of the black-capped chickadee

Chickadee Distribution Model
UMaine model of current chickadee distribution
Chickadee Distibrution - Hadley Centre Data
Predicted chickadee distribution based on Hadley Centre data
Chickadee Distribution - Canadian Centre Data
Predicted chickadee distribution based on Canadian Centre data

The computer model developed by University of Maine Professor of Wildlife Ecology Raymond O'Connor and former graduate student Steve Matthews successfully used climate and landscape data to reproduce distribution maps for 150 species of birds, including the black-capped chickadee (above). The scientists then used data on climate change and its impact on eastern forests to predict the future ranges of these species. Based on predictions from the Hadley Centre for Climate Prediction and Research in England, and the Canadian Centre for Climate Modeling and Analysis, the UMaine model found the distribution of the chickadee greatly diminished.

Using the 150 bird species for which they had reliable information, the UMaine scientists built the forest data into their own models. They also used two climate change scenarios, one from the Hadley Centre for Climate Prediction and Research in England, and one from the Canadian Centre for Climate Modelling and Analysis (CCCma). When they ran their model for each of the 150 species, the results surprised Matthews, who had worked on ornithology research projects in the mid-Atlantic states and the South before he came to New England.

"More than half the species were projected to lose at least 25 percent of their current abundance in the eastern U.S. That's a lot; a big surprise. It doesn't mean that they would go extinct. Many would probably increase their range in Canada, but we'll lose them in large parts of the U.S.," Matthews says.

The most significant changes occurred in the southern portions of birds' ranges. In some cases, the model suggested that certain birds would disappear altogether from that portion of their current range. In other cases, a species might change from being abundant in an area to being rare. The results also showed that a small number of species would increase their ranges.

"Many bird species are limited in their distribution by climatic constraints and by their habitat, such as where a particular type of forest is located," says O'Connor. "We were able to work out where and in what numbers each bird species would survive for the eastern U.S. a first in climate change studies. Previous work considered only the climate envelope, not the joint effects of shifting habitat (forest) and shifting climate."

Among the species projected to become less abundant across the East are Maine's state bird, the black-capped chickadee (Parus atricapillus), the song sparrow (Melospiza melodia) and the American robin (Turdus migratorius). In Maine itself, the model estimates that black-capped chickadees and robins are likely to see little change, while song sparrows could decline significantly.

Predicting the future, even with the most up-to-date information, is always tricky. Whether bird species actually shift their ranges in the future as the UMaine model suggests depends on climate and biology. If climate changes as the Hadley and Canadian climate models suggest, and if the birds maintain their present relationship to climate and habitat, then the UMaine model results may come to pass.

"The uncertainty is about the exact pattern of climate change (Hadley and CCCma are extremes) and whether the birds might adapt to change in ways they do not now display, such as by changing their temperature tolerances or by turning to other new (habitat) types in which to nest," says O'Connor.

The Forest Service has published the research on trees by Iverson and Prasad and posted it on the Web.

In October, the Forest Service also published UMaine's bird species maps in Atlas of Climate Change Effects on Common Birds in the Eastern United States. Funding for the atlas included support from UMaine's Office of the Vice President for Research and the College of Natural Sciences, Forestry, and Agriculture.

Matthews' research received financial support from the Forest Service and the Department of Wildlife Ecology at UMaine. He is now a Ph.D. student at Ohio State University studying the ecology of migration in birds.

by Nick Houtman
January-February, 2005

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