Wild populations of great tits and earlier springs

(26.04.2013) 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 timingGreat tit nestlings when that timing shifts.

Bernt-Erik Sæther, an NTNU biologist 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.

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.

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 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."