Timekeeping birds unlock early migration mystery

Written by Planet Earth Online
The remarkable timekeeping of birds could finally explain how some bird species are able to respond to climate change by migrating earlier and earlier each year.
Black-tailed Godwit. © Andreas Trepte

Black-tailed Godwit. © Andreas Trepte

According to a new study, individual Black-tailed Godwits migrate at more or less the same time every year. But the migration of the population as a whole seems to be happening progressively earlier.
Dr Jenny Gill of the University of East Anglia, who led the research, explains:
The only explanation that’s left, is that new birds are hatching and migrating earlier. As the older birds die off, the population fills up with early migrators.
Climate change is likely to be driving this change because Black-tailed Godwits nest earlier in warmer years. Birds that hatch earlier are likely to have more time to gain the body condition needed for migration, and to find good places to nest in the winter.
The team have monitored a population of Black-tailed Godwits for over 20 years. The citizen science project relied on the help of more than 2,000 bird-watching volunteers across Europe.
In winter, the wading birds can be found in estuaries all the way down the west coast of Europe, as they flee the harsh Arctic conditions of their Icelandic home.
It’s long been known that birds tend to return to the same place each time they migrate: that’s why many of the characters in your garden will be familiar to you.
But the new study, published in The Proceedings of the Royal Society B, is the first to show they also return at the same time, within just a few days. Dr. Gill says:
They can tell the time. I have no idea how, but they can.
We thought that individual birds might migrate earlier or later in response to the weather. But it seems that, whatever the weather, they migrate at almost exactly the same time every year; it’s quite remarkable.
If you think about it from the bird’s point of view, it makes sense. You know that the place you’ve been to before will be available, and you know that it will be available at that time.
Other studies have shown that birds which migrate over longer distances have found it difficult to adapt their migration cycles to a changing climate. Many of those species are also suffering rapid decline. The study could explain why those birds are struggling to respond. Dr. Gill also added:
Many long-distance migrants arrive so late on to the breeding grounds that they only have a short time in which to mate and nest. They simply don’t have time to respond to warming conditions by nesting earlier.
Reference: Jenny Gill, Jose Alves, William Sutherland, Graham Appleton, Peter Potts and Tomas Gunnarsson, ‘Why is timing of bird migration advancing when individuals are not,’ Proceedings of the Royal Society B, 2013
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