Migrating birds are staying longer in UK before heading for Africa
MIGRATING birds such as swallows and house martins are increasingly reluctant to leave the UK and return to Africa, apparently taking advantage of longer and warmer summers in Europe, new research has found.
They may even be nesting more often.
The study in the international science journal, Global Change Biology, says migrant birds that arrive at their breeding grounds early in spring might be expected to depart early in autumn too, as soon as their chicks have fledged. But in consecutive seasons that didn’t happen.
The research used daily observations of migrant birds from the remote Fair Isle Bird Observatory, between Orkney and Shetland, to measure how spring and autumn migration timing has changed over 60 years.
Dr Will Miles, of the Fair Isle Migration Project, says “Environmental conditions are changing rapidly at a global scale.
“In response to these changes, the seasonal lifecycles of plants and animals are shifting too, often in dramatic and unexpected ways.
“It’s too early to know for sure exactly why bird migrations now last so much longer in spring and autumn, but it’s possible that conditions in Europe and Africa have gradually become more favourable for long-distance migration, and the birds are now under less pressure to migrate quickly within a short time window.”
He said that for example on Fair Isle, swallows and house martins were migrating up to a fortnight later than they did a few decades ago. Willow warblers used to migrate within a five-week period in spring but now this species is seen on migration for up to 10 weeks.
“Some species appear to be staying in Europe for longer in the summer and may breed several times, and that is an advantage for the birds,” he said.
He added this latest test analyses demonstrated that long-term changes in migration timing can be more complex than widely assumed.
The Fair Isle Migration Project is a scientific collaboration between the Fair Isle Bird Observatory Trust and the University of Aberdeen.
The island is a major centre for bird migration and a daily census has kept census counts of migrant birds there.
The permanent bird observatory was founded by George Waterston after the Second World War.