Birds Getting Bigger as Climate Changes
Major New Study by PRBO and Partners
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Press Release:
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Bigger Birds in California, Courtesy of Global Climate Change
SAN FRANCISCO, October 31, 2011 -- Birds are getting bigger in central California, and that was a big surprise for Rae Goodman (SF State) and her colleagues from PRBO Conservation Science and the San Francisco Bay Bird Observatory.
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Goodman uncovered the trend while working as a graduate student for SF State biologist Gretchen LeBuhn, analyzing data from thousands of birds caught and released each year by scientists from PRBO Conservation Science (PRBO) and the San Francisco Bay Bird Observatory (SFBBO).
The team of scientists from San Francisco State, PRBO and SFBBO, found that birds’ wings have grown longer and birds are increasing in mass over the last 27 to 40 years.
Biologists have recognized that plants and animals in many parts of the world are changing their body size in response to climate change – but in most places they are getting smaller.
Using 40 years of data from the Palomarin Field Station in coastal California, and 27 years of data from the Coyote Creek Field Station in southern San Francisco Bay, the authors quantified changes in the weight and wing length of both resident and migratory birds. Expecting to find that birds were getting smaller, the authors were surprised to discover that weight and wing length have been increasing. The results demonstrate that decreasing body size in response to climate change is not universal.
That animals can respond to environmental changes – even rapid climate change – could be viewed as good news. Changes in body size in California and other parts of the World suggest that species are adapting to climate change.
“The fingerprint of climate change is showing up in many of our ecosystems” explains Nat Seavy, Research Director for the Central Coast at PRBO Conservation Science, “the challenge is to use the long-term data we’ve been collecting to understand how, where, and why these changes are occurring.”
What’s making the birds bigger? The researchers think that the trend is due to climate change. Climate change affects body size in a variety of ways, they note in their paper. For instance, birds might get bigger as they store more fat to ride out severe weather events, which are expected to be more common under global climate change. Climate change could also alter a region’s plant growth, which may eventually lead to changes in a bird’s diet that affect its size.
LeBuhn, an assistant professor of biology, said she was “completely surprised” to find that the central California birds were growing larger over time. “It’s one of those moments where you ask, ‘what’s happening here?’” The results were so unexpected, she said, that the findings made them take a step back and look more closely at how climate change could influence body size.
The bird data come from two long-term research stations in central California, where a wide variety of birds are captured, banded about the leg with an identification tag, and weighed and measured before being released unharmed. Many of the same birds were captured each year, allowing the researchers at the sites to build up a unique database that could be used to track changes among the birds over several decades.
The team of researchers used data from 14,735 individual birds collected from 1971 to 2010 at PRBO’s Palomarin Field Station, near the southern end of the Point Reyes National Seashore, and 18,052 birds collected between 1983 and 2009, from SFBBO’s Coyote Creek Field Station at the southern end of the San Francisco Bay.
“At the time I started my research, a few studies had looked at body size changes in a few species in Europe and the Middle East, but no one had examined bird body size changes in North America,” said Goodman, who now teaches Biology and Environmental Science at San Francisco’s Jewish Community High School of the Bay.
“We had the good fortune to find an unexpected result—a gem in research science,” she added. “But we were then left with the puzzle of figuring out what was going on.”
After testing and discarding of a number of other explanations, Goodman and her colleagues were confident that climate change was behind the longer wings and bigger bodies in most of the birds. The birds may be responding to climate-related changes in plant growth or increased climate variability in central California, the researchers suggest in the paper.
The findings offer a glimpse at the potent effects of climate change across a wide range of species, LeBuhn said. “Even over a pretty short period of time, we’ve documented changes in important traits like body size, where we don’t expect to see much flexibility.”
“But in some ways,” she added, “it gave me a little more hope that these birds are able to respond—hopefully in time—to changes in climate.”
“Although it is encouraging that species are changing in response to climate change, “said Nat Seavy, Research Director for the Central Coast at PRBO Conservation Science, “it is also troubling that environmental stressors are pushing and pulling on species in diverse ways. What will happen to our ecosystems as some species get larger and others get smaller? We need long-term monitoring to help us understand the impact of these changes.”
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