Climate change may be causing local birds to grow longer wings and bigger bodies, according to a study released Monday by PRBO Conservation Science.
The research is based partly on data collected within the Point Reyes National Seashore that suggests that over the past 40 years birds such as sparrows, chickadees and robins are growing. Researchers suggest the birds are adapting to harsher weather conditions such as heavy El Nino storm years.
That animals can respond to environmental changes -- even rapid climate change -- could be viewed as good news showing species can adapt, researchers said.
"The growth we saw is very small, but it is statistically significant," said Nat Seavy, research director for the Central Coast at PRBO Conservation Science. The study estimates a growth rate in the birds of 0.05 percent each year in the past four decades.
"The fingerprint of climate change is showing up in many of our ecosystems," Seavy said, adding that much of the data were collected from the Palomarin Field Station, near the southern end of the Point Reyes National Seashore, north of Bolinas. "The challenge is to use the long-term data we've been collecting to understand how, where, and why these changes are occurring."
Researchers suggest the change may be occurring as birds gird for rougher weather by storing more fat. Another theory has the changing weather patterns growing more vegetation in the region, increasing food supply and allowing birds to grow larger.
San Francisco State University graduate student Rae Goodman analyzed data from thousands of birds caught and released each year by scientists from PRBO and the San Francisco Bay Bird Observatory.
"It's one of those moments where you ask, 'what's happening here?'" said Gretchen LeBuhn, an assistant professor of biology at the university, for whom Goodman was working.
She said she was "completely surprised" to find that the birds were growing larger over time and that the findings made them take a step back and look more closely at how climate change could influence body size.
The bird data for the study came from two long-term research stations -- at Palomarin and the Coyote Creek Field Station at the southern end of the San Francisco Bay -- where a wide variety of birds are captured, banded about the leg with an identification tag, and weighed and measured before being released. The team of researchers used data from 14,735 individual birds collected from 1971 to 2010 at Palomarin and 18,052 birds collected between 1983 and 2009 from the Coyote Creek Field Station.
"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 -- but we were then left with the puzzle of figuring out what was going on."
After testing and discarding 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 data were published last month in the journal Global Change Biology.
"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," LeBuhn said. "But in some ways it gave me a little more hope that these birds are able to respond -- hopefully in time -- to changes in climate."
The research also shows how climate change is changing the natural world, researchers said.
"It is ... troubling that environmental stressors are pushing and pulling on species in diverse ways," Seavy said. "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."