Great tits cope well with warming

Food for hungry mouths

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At least one of Britain's birds appears to be coping well as climate change alters the availability of a key food.

Researchers found that great tits are laying eggs earlier in the spring than they used to, keeping step with the earlier emergence of caterpillars.

Writing in the journal Science, they point out that the same birds in the Netherlands have not managed to adjust. Understanding why some species in some places are affected more than others by climatic shifts is vital, they say.

The Royal Society for the Protection of Birds (RSPB) commented that other species are likely to fare much worse than great tits as temperatures rise.

Perfect timing

The research uses a long record of great tits in a breeding site at Wytham Woods near Oxford, where observations began in 1947.

The finding is surprising in that the birds are using the same old rules, but the rules still work Professor Marcel Visser

"We think it’s the longest running population study of wild animals anywhere in the world where animals are marked (ringed)," said Ben Sheldon of Oxford University, who led the new research.

"The population contains about 400 breeding pairs, and they produce between them 2,000 or more offspring each year - so over the course of the study about 80,000 birds have been ringed and studied," he told BBC News.

The current work used records going back only to 1961, when a standard methodology was adopted.

The great tits are laying eggs now about two weeks earlier in the year than they were 47 years ago.

The timing is crucial, because for the two-week period after they hatch, the chicks have to gobble down huge quantities of winter moth caterpillars which only emerge for a short period.

"Winter moth larvae can make up up to 90% of the biomass of insects on oak trees at that time," said Professor Sheldon.

"Great tits have eight or nine babies in a brood, and each of them will eat about 70 caterpillars a day.

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The chicks hatch and are fully grown within two weeks, so they need something that's really abundant - that's why they synchonise their breeding so hatching co-incides with the emergence of the caterpillars."

The caterpillars' appearance is triggered by ambient temperature - that has been shown in the laboratory - and it is believed that great tits also begin their breeding cycle in response to temperatures.

Their movement to an earlier breeding time does not involve an evolutionary change, the scientists believe - it is simply that individual birds are able to change their behaviour, in the same way that they have presumably adapted to warmer or cooler phases before the era of human-induced global warming.

Different strokes

In Wytham, the behaviour of the two species is changing in step; but other situations are very different.

Three years ago, Marcel Visser from the Netherlands Institute of Ecology in Heteren collated a number of these cases.

The North American wood warbler has not adapted its migration pattern to the earlier emergence of caterpillars in its breeding ground, and the Dutch honey buzzard is also failing to adapt to the earlier appearance of wasps, which it eats.

The red admiral butterfly is arriving on the UK's shores earlier from its winter grounds in north Africa; but the staple food of its larvae, the common nettle, continues to flower at the same time each year.

Wytham Woods are home to about 400 breeding pairs of great tits

Just across the North Sea in Holland, Professor Visser has also found that great tits are faring very differently from their British cousins; the breeding time is advancing each year, but the emergence of caterpillars is advancing three times faster.

"The UK finding is to some extent surprising in that the birds are using the same old rules, but the rules still work," he told BBC News.

"In our study population, the same old rules don't work any more; so it's an interesting question as to which situation is the normal one and which is the exception."

The RSPB and other conservation bodies have regularly warned that climate shifts could have a devastating impact on some species; and they believe the new research does not change that picture.

"It's great to hear that the great tit is able to keep pace with the rapid rate of climate change, but then it's probably in the best place to do that," observed RSPB spokesman Grahame Madge.

"They're abundant birds, they can live in gardens, woodland and open country, and they churn out large numbers of young in a short space of time, so they're better able to learn changes in behaviour."

The organisation believes - as do others - that climate change is one of the main cuplrits for the abrupt declines in some seabird populations around UK coasts in recent years.

The Oxford and Heteren groups are now planning to collaborate on a study to elucidate why some populations apparently adapt well to climate change, and others do not.

"Our study shows that sometimes individuals can be very flexible in their behaviour," said Ben Sheldon.

"What we want to do is to try and understand why some species are flexible and others aren't - it's the ones that aren't flexible that are going to be at risk."

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