Against expectations, U.S. West Coast birds are increasing in size as climate changes

By RACHEL NUWER
3 November 2011
As we noted here in a recent post, a substantial body of research indicates that species tend to become smaller as a result of global warming and other climate change patterns. So researchers in California were surprised to find that West Coast birds, on the contrary, have been growing larger in recent decades. “We went into this expecting to find that birds are getting smaller, because that’s what’s been seen before,” said Rae Goodman, a biologist and the lead author of a new paper detailing the trend in the journal Global Change Biology. “The finding that birds are getting bigger draws into question what’s driving the change in size.” Ms. Goodman and her colleagues analyzed data dating back 40 years from two different California bird observatories. Body-mass and wing-span measurements of nearly 33,000 birds representing dozens of species collected from 1971 to 2010 were analyzed for variations over time. The researchers found that wing length had been steadily increasing and body mass had expanded. Some of the species migrate between Alaska and Latin America, while others breed locally or are short-distance migrants, but the rate of change in size did not depend on where the birds spent the majority of their longitudinal time. “This is a very thought-provoking find based on a really impressive data set,” said Josh Van Buskirk, a zoologist at the University of Zurich who was the lead author of the only other paper investigating changes in bird size in North America. Dr. Van Buskirk’s work took place in the eastern United States, and he found just the opposite trend: eastern birds are shrinking rather than growing. “What they point out is, hey — it’s not just temperature driving the change,” Dr. Van Buskirk said. What is needed now, he added, is an explanation of the environmental drivers of the changes in size. […]

Birds Fly in the Face of Climate Change Expectations