Climate change hits migrating birds

Climate change has altered the nesting patterns of birds resulting in earlier migrations, experts have found.

It has long been suspected that birds are migrating earlier each year to cope with changes in their environment, b ut research by the University of East Anglia (UEA) has found that the phenomenon is more complex.

Individual birds migrate like clockwork arriving at the same time each year, according to the study. However, younger birds are migrating earlier because of changes to nesting and hatching patterns.

Dr Jenny Gill, from the UEA's school of Biological Sciences, said: "We have known that birds are migrating earlier and earlier each year - particularly those that migrate over shorter distances.

"But the reason why has puzzled bird experts for years. It's a particularly important question because the species which are not migrating earlier are declining in numbers."

The research team looked at a population of Icelandic black-tailed godwits over 20 years. During this time period, the flock advanced their spring arrival date by two weeks.

"The obvious answer would be that individual birds are simply migrating earlier each year," Dr Gill said.

"But our tracking of individual birds shows that this is not the case.

"In fact individual birds do almost exactly the same thing every year - arriving punctually at the same time year-on-year.

"Because we have been following the same birds for so many years, we know the exact ages of many of them."

Birds hatched in the late 1990s arrived in May, but those hatched in more recent years are tending to arrive in April.

Dr Gill added: "The arrival dates are advancing because the new youngsters are migrating earlier.

"Climate change is likely to be driving this change because godwits nest earlier in warmer years, and birds that hatch earlier will have more time to gain the body condition needed for migration and to find good places to spend the winter, which can help them to return early to Iceland when they come back to breed."

She added that advances in migration timing are not common among species migrating over long distances because m any long-distance migrants arrive so late on the breeding grounds that they have little opportunity to respond to warming conditions by nesting earlier.

"This research is very important because many long-distance migrant bird populations are currently declining very rapidly, and identifying how climate change is affecting these populations is a key part of understanding the causes of these declines," Dr Gill added.

The research team has been supported by a network of more than 2000 birdwatchers who reported sightings of colour-ringed black-tailed godwits as they travel from Iceland to Spain and Portugal.

The research was funded by Natural Environmental Research Council.