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Climate change not effecting Great tit populations - More hatchlings die - More juveniles survive

08/05/2013 07:41:28

Great tit (Parus major) hatchlings suffer from lower availablity of caterpillars in the spring, but overall great tit populations have managed to survive. Photo: Arnstein Rønning

Wild populations of great tits and earlier springs - Courtesy of The Norwegian University of Science and Technology (NTNU)

May 2013. What happens when climate change makes for a food timing problem for great tit populations? Norwegian, French, American and Dutch researchers have explained (In Science magazine) that while more hatchlings may die, greater juvenile survival and immigration have surprisingly kept populations stable.

Earlier springs
One of the many changes that results from global warming is a shift to earlier springs - something that has led many biologists to worry what will happen to populations that have adapted to specific events with precise timing when that timing shifts.

Caterpillars hatching earlier
Earlier springs have caused caterpillars to hatch and grow earlier than they used to. But great tits, which catch caterpillars to feed their young, have not been able to advance their timing of egg-laying to keep pace with the caterpillars. This has caused an increasing mismatch between the peak availability of caterpillars and the hatching of baby great tits, which has caused early offspring survival in great tits to decline.

A great tit. Photo: Marek Szczepanek

A great tit. Photo: Marek Szczepanek

Juvenile survival rates up
That might make you think that great tit populations would also go into decline, but nearly four decades of data on great tit populations shows that this loss of great tit young in the spring has been offset by increased juvenile survival as well as increased immigration during winter. Thus, the mismatch in timing has not caused a decline in pre-breeding population size.

The researchers observe that their findings "imply that natural populations may be able to tolerate considerable maladaptation driven by shifting climatic conditions without undergoing immediate declines."

Bernt-Erik Sæther, a biologist at the Norwegian University of Science and Technology and director of the university's Centre for Biodiversity Dynamics, was a co-author on a paper published Friday, 26 April in Science magazine that explores this problem.

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