'Early birds' beat the climate

11:20am Thursday 15th May 2008

Research carried out by Oxford scientists shows that great tits breeding in Wytham Woods have adapted their breeding to fit warmer springs, writes ANDREW FFRENCH

Great tits in woods near Oxford have adapted their breeding patterns to fit warmer springs brought on by climate change, an Oxford University study has revealed.

Research carried out by scientists showed that, over almost 50 years, a population of birds breeding in Wytham Woods were laying their eggs almost 14 days earlier on average.

The data collected from nearly 10,000 breeding reports shows an overall trend of birds laying eggs earlier in response to warmer spring temperatures.

The change in their behaviour enables them to make the most of seasonal food - a bonanza of caterpillars that now also occurs around two weeks earlier due to warmer temperatures.

The data, which stretched from 1961 to 2007, revealed there was a close relationship between the average date birds laid their eggs and spring temperatures.

According to Prof Ben Sheldon, of the Department of Zoology, the study showed changes were driven by individual birds adapting their behaviour rather than genetic evolution.

"We found that, in this great tit population, female birds are able to adapt their behaviour from year to year to respond to changing environmental conditions.

"They sense their environment and breed at the right time when these caterpillars are most abundant in their environment."

Prof Sheldon added: "We think it's the longest running population study of wild animals anywhere in the world where animals are marked (ringed)."

The earlier egg-laying allows the birds to make the most of the availability of winter moth caterpillars, which are also at their most abundant two weeks earlier because of warmer weather.

The moth larvae are a key source of food for the rapidly growing great tit chicks.

Prof Sheldon said the birds had kept track with the changes that had occurred in their natural surroundings over recent decades.

The study also found there was very little variation between different females as they followed the "early bird" trend.

The findings were in contrast to research into Dutch great tits which found much greater variation between individuals in their ability to adapt to a changing climate. Prof Sheldon, one of the lead authors of the study, published in the journal Science, said more research was needed to see if the close matching of changes in egg-laying and the environment found in their study was unusual.

He concluded that while some species may be able to track environmental changes through individual flexibility, others may only adapt through natural selection, favouring those most able to respond to changes, with overall populations affected as a result.

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