May 10, 2008

British Bird Adapts Well to Climate Change

British researchers have discovered a bird species, called great tits, that has adapted to climate change by breeding earlier in the year. By doing this, the tits are able to keep apace with the earlier emergence of the caterpillars on which the birds feed. 

Interestingly, while the researchers observed this behavior in the British birds, the same birds in the Netherlands did not adjust to the shift in climate. The Royal Society for the Protection of Birds (RSPB) told BBC News that as temperatures rise other species are likely to fare much worse than great tits.

The research provide insight into why certain species in some locations are more affected than others by climate change, something the scientists say is vital.

The research is based on a long historical record of great tits in a breeding site at Wytham Woods near Oxford.  Although observations began in 1947, a standard methodology was not adapted until 1961, and the current work is based on these records.

"We think it's the longest running population study of wild animals anywhere in the world where animals are marked (ringed)," Ben Sheldon of Oxford University, the study's lead researcher, told BBC News.

"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 said.

The great tits are now laying their eggs about two weeks earlier than they did 47 years ago. Timing is critical because the winter moth caterpillars emerge only for a short time, and an adequate food supply for the chicks depends upon coordinating the hatching of the chicks to the availability of the caterpillars.

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

"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 synchronize their breeding so hatching coincides with the emergence of the caterpillars."

Laboratory research has shown that ambient temperature triggers both the appearance of the caterpillars and the breeding of the great tits.   The scientists believe the shift to earlier breeding cycles is not a result of evolutionary change, but simply a matter of individual birds changing their behavior.

Although in Wytham both caterpillars and great tits and seem to be moving in lock step, this is not the case in other areas. 

Marcel Visser from the Netherlands Institute of Ecology in Heteren began assembling a number of these cases three years ago.

Visser noted the Dutch honey buzzard that has not adapted to the earlier appearance of the wasps they feed upon, and the North American wood warbler, which has failed to adapt its migration pattern to the earlier emergence of caterpillars in its breeding ground.

In the UK, the red admiral butterfly is appearing on shore earlier from its winter grounds in north Africa, despite the fact that the common nettle, the staple food of its larvae, continues to flower at the same time each year.

Of particular interest, Visser noted that in Holland the great tits exhibit different behavior than they do in Britain, in that the breeding time is only advancing a third as fast as the caterpillars.

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

"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 routinely cautioned that shifts in climate could have a devastating impact on some species, a view they believe is supported by the new research.

"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," RSPB spokesman Grahame Madge told BBC News.

"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 behavior."

The organization, along with others, believes climate change is one of the main factors driving the sudden declines in some seabird populations in recent years along the British coasts. The Heteren and Oxford groups are now planning to partner on research that would clarify why some populations appear to adapt well to climate change, while others do not.

"Our study shows that sometimes individuals can be very flexible in their behavior," Ben Sheldon told BBC News.

"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."

The study was published in the journal Science.  An abstract can be viewed here.