Extract from 'Nature' 17th May 2001
A migratory bird has not keep pace with climate change. To adjust to warmer springs in their Dutch breeding grounds, pied flycatchers (Ficedula hypoleuca) lay their eggs earlier. But the timing of their migration from Africa has not altered, putting them under pressure to breed and feed quickly1.
The life cycles of migratory animals must fit with all the environments in which they spend time. This makes them vulnerable to climate change, as it is unlikely that change will be the same in all areas, or that all aspects of an animal's behaviour will be governed by the same environmental cues.
Christiaan Both, of the University of Groningen in The Netherlands, and Marcel Visser, of the Netherlands Institute of Ecology in Heteren, have studied the recent changes in flycatcher breeding patterns. Between 1980 and 2000 the average spring temperature in The Netherlands rose by about 3 ºC. So the peak in insect populations — with which the birds' breeding was timed to coincide — shifted to earlier in the year.
The average date of egg laying has correspondingly moved, to about ten days earlier than its previous point in the middle of May. But flycatchers are still arriving between the middle of April and the middle of May, presumably because day length or some internal clock times their departure from Africa.
"An uncoupling of the weather in Africa and The Netherlands [means] the rules the animals use are no longer valid," Visser explains. "The flycatchers used to arrive three weeks before they began laying, which gave them time to recover from their long journey. Now they have to start laying as soon as they get here." And many latecomers arrive to find that the food is past its best.
As well as reducing the number of offspring the birds can raise, the effort of hurried breeding may kill off many fatigued birds. "If they don't find a way to advance their arrival date, they'll be stuck," says Visser. He suspects that climate change may be a factor in the recent population declines seen in many migratory birds.
Terry Root, of the University of Michigan in Ann Arbor, has found that many American birds are changing their migration times or shifting their ranges northwards or uphill to cooler climes. Nature reserves should be designed to take account of these changes, she suggests — running north–south, for example — to give species somewhere to go.
But she is pessimistic about nature's ability to adapt to the pace of climate change. As predators, prey and their environments become out of sync, she says, natural communities will "tear themselves apart".
"There's going to be a mass extinction of species," she concludes. "We're
in for some really difficult times ahead."