(Aug. 12, 2005) -- 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 animals -- as during past climate changes -- to shift their habitat ranges and to alter the timing of events like breeding and hibernation.

But these changes -- like the warming itself -- are 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 seabirds -- like kittiwakes, terns, and guillemots -- failed 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.

And as researchers come to grips with current conditions, their forecasts for the future grow gloomier.

Expectations and Timing

In 2003 Stanford's Terry Root found many examples of global-warming-spurred behavioral shifts in a review of 143 scientific studies covering 1,473 species of plants and animals.

"If you look at all the studies that have been done on species and climate change and find the same signature for species all around the globe by many, many individuals instead of just one or two, it gives circumstantial evidence" that global warming is driving the changes, she said.

And the changes are "not moving in lockstep," Root noted. Some species are moving to new habitats quickly, others slowly, some not at all. This breaks up established predator-prey interactions, for example, leaving ecosystems disrupted.

Galbraith, who co-authored a 2004 report for the Washington, D.C.-based Pew Center on Global Climate Change, said the behavioral shifts are anticipated, but they are coming about 15 years earlier than he expected.

"One important message from the Pew report is we're already seeing these effects, and they're widespread … the effect is way ahead of when many people in the field would have predicted," he said.

Looking to the Future

According to the UN's Intergovernmental Panel on Climate Change, the average global temperature could rise by an additional 2.5º to 10.5ºF (1.4º to 5.8ºC) by 2100, if the amount of carbon dioxide in the atmosphere doubles as expected.

"If we are seeing changes at one degree [Fahrenheit], what might we expect at four and five degrees?" Galbraith said.

Though the climate has shifted several times in the past, scientists say the pace of the temperature swings were much slower, giving plants and animals more time to adapt to changing conditions.

"The other factor is, the face of the planet doesn't look anything like it did when the other changes happened," Root said. "Now we have Kmart parking lots everywhere. If you are an organism that needs to disperse north in North America, and you run into the city of San Diego, say, what do you do?"

According to Root, many species will be unable to navigate through the human landscape. When the temperature gets too hot, they'll die. A temperature rise of a few degrees may cause an eighth to a quarter of all species to go extinct, she speculated.

"If we go six to ten degrees [higher], we're really right on the brink of a huge mass-extinction event. And I don't know that people understand what that means," she said.