Researchers have noticed that birds have been embarking on their big migration earlier every year; and they think it might have something to do with climate change.
Warmer climates have led to earlier nesting and hatching, which in turn could be leading to earlier migration, a University of East Anglia news release reported.
"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," Lead researcher Doctor Jenny Gill from UEA's school of Biological Sciences, said.
In order to reach their conclusion, the team observed Icelandic black-tailed godwits over the course of 20 years. They watched as the birds advanced their migration arrival date by two weeks over that period of time.
"The obvious answer would be that individual birds are simply migrating earlier each year. 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," Gill said.
Since the researchers had been following the flock for so long they knew many details about the individual birds, such as their exact ages. The older birds were more stuck in their ways, and still tended to arrive in May; but some of the younger birds (hatched after the 1990s) have been arriving in April.
"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," Gill said.
Global warming does not seem to be having as strong of an effect on birds with longer migration patterns.
"Many long-distance migrants arrive so late on the breeding grounds that they have little opportunity to respond to warming conditions by nesting earlier," Gill said.
"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," she said.
