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Default British Birds Adapt to Changing Climate

Climate change threatens many animals -- but with any luck, some will handle weather shifts with as much aplomb as Parus major, a colorful songbird also known as the great tit.
In a study published today in Science, ornithologists from the University of Oxford tracked the egg-laying times of great tits in Wytham, England. Since the mid-1970s, temperatures in Wytham have risen steadily, hastening the start of spring by two weeks. The birds have followed suit, timing their breeding to coincide with earlier hatches of their favorite food source, a species of moth caterpillar.
The birds' adaptation appears to be based in what's known as phenotypic plasticity -- the ability of a creature to respond to changes in its environment -- rather than natural selection favoring birds with earlier breeding times.
Such plasticity allows the birds to respond quickly to climate change. Although there's no guarantee that they could handle more-radical warming, the findings strike a rare optimistic note in a chorus of warnings about climate-change-induced animal doom.
"These changes were driven not by evolution, but by the inbuilt ability of individuals to respond to their environment," said study co-author Ben Sheldon. "If driven by natural selection, this adaptation wouldn't have happened so rapidly. In terms of matching environmental change, this is more effective."
Great tits walk a fine line. If they lay their eggs just a few days late, the winter moth caterpillars on which they rely for springtime sustenance will have already hatched and departed when their chicks are hungriest.
But some environmental cue -- most probably temperature-related, though the researchers aren't sure -- triggers timely egg-laying in Wytham's great tits. Whether spring comes early or late, they've laid their eggs on time ever since scientists started tracking them in the early 1960s.
This versatility, said Sheldon, is produced by individual adaptive mechanisms, rather than long-term calibration by natural selection that favors earlier-laying birds.
"The temperature is changing in one direction, but each year it fluctuates a little bit. Natural selection would have trouble keeping up with those fluctuations," said Sheldon.
Such plasticity is good news for the birds.
"You can have rapid evolutionary responses to climate change -- but plasticity, if it does the right thing, can occur more quickly," said Andrew Hendry, a McGill University biologist who has studied the effects of climate change on animals.
"If plasticity is common in these traits that are influenced by climate change, it will aid population persistence," added Hendry, who was not involved in the study.
The findings in Wytham run contrary to those in another great-tit population in the Netherlands. Though they experienced similar weather patterns, the Dutch birds failed to lay their eggs on time.
Some populations may prove better able than others to handle climate change, said Sheldon, but he warned against expecting plasticity to handle the worst of our greenhouse excesses.
"We've seen these birds adapt to a 1.5-degree rise over the last three decades, but there's no guarantee they could cope with another five degrees," he said.


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