for National Geographic News
The world on average is about 1ºF (0.6ºC) warmer today than it was a century ago. That may not sound like a lot, but it's enough to concern some scientists.
The temperature rise has put feathered, furry, and scaly animals alike in a state of flux. Some are seeking higher ground, others are breeding earlier, and many can't find enough to eat.
Scientists expect the current bout of global warming to cause animalsas during past climate changesto shift their habitat ranges and to alter the timing of events like breeding and hibernation.
But these changeslike the warming itselfare already happening more quickly than most researchers expected.
In the North Sea, for example, such changes have kinked the entire food chain, according to Euan Dunn, head of marine policy for the U.K.'s Royal Society for the Protection of Birds.
Many species of seabirds are failing to breed there because of a sharp decline in the population of sand eels, which the birds eat. Sand eel numbers, in turn, are dwindling because the cold-water plankton on which they feed is being replaced by plankton that thrives in warm water.
"Everyone realizes something very serious is going wrong here," Dunn said. Tens of thousands of seabirdslike kittiwakes, terns, and guillemotsfailed to breed in 2004. While it's too early to tell this year, Dunn said, sand eel populations are low again so far.
In Costa Rican rain forests, meanwhile, warmer temperatures have allowed normally lowland toucans to invade the high-altitude refuge of endangered quetzal birds. The quetzals have nowhere to go, so they nest in tree cavities within easy reach of the toucans who feast on quetzal eggs and chicks.
"There's a lot of concern this will have a major impact on quetzal populations," said Terry Root, an ecologist at Stanford University in Palo Alto, California.
Then there are tree swallows, which are showing up to their U.S. breeding grounds about 12 days earlier than they were 30 years ago, according to Hector Galbraith at the University of Colorado at Boulder.
"The result in and of itself would be interesting but hardly worrying," Galbraith said. "But when you look at other [bird] species and see this 10-to-12-day change crop up in tons of those, it is [worrying]."
Galbraith, Root, and Dunn are part of a growing chorus of scientists and conservationists sounding an alarm that global warming is changing not just ecosystems but the behavior of animals that live in them.
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