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Great tits cope well with warming
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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.
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The finding is surprising in that the birds are using the same old rules, but the rules still work
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"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.
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
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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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