British birds are nesting earlier ...

Birds in the United Kingdom have adjusted their nesting habits to accommodate climate changes, according to an analysis of 57 years of data on egg-laying.

In the cool spell of the 1960s and 1970s, British birds began laying eggs later in the year than they had before, the study shows. In recent years, however, a warmer climate has prompted the birds to push their nesting calendars forward.

"Birds that lay earlier produce more young and healthier young who have a better chance of surviving until the following year, so in that sense [the trend] could be quite a good thing," says Humphrey Q.P. Crick of the British Trust for Ornithology in Norfolk, England. "But it could be a bad thing if the food supplies that the chicks rely on don't shift in the same way."

Crick and coauthor Timothy H. Sparks of the Institute of Terrestrial Ecology in Cambridgeshire, England, tracked the nesting habits of 36 bird species throughout the United Kingdom.

The study indicates that the average egg-laying date for 31 species is linked to temperature or rainfall. Temperature, particularly in March and April, explained long-term trends in laying time for 17 species, the researchers report in the June 3 NATURE.

Previously, researchers had noted trends toward earlier laying, says Crick (SN: 8/30/97, p. 141). "Then, we sort of waved our arms a bit and said, `It's likely to be global warming,'" he adds, "but now we're showing that all of these changes can really be explained statistically in terms of changes in temperature."

On the basis of projected climate changes, Crick and Sparks estimate that by 2080, 27 bird species will have moved their egg laying schedule forward by 8 to 18 days.