Climate change will force bone-weary birds migrating to Europe from Africa to log extra mileage, with possibly devastating consequences, according to a study released on Wednesday.

The annual voyage of some species, which fly north in search of food and suitable climes, could increase by as much as 400 kilometres (250 miles), the research found.

"Marathon migrations for some birds are set to become even longer," said Stephen Willis, a professor at Durham University in Britain and the main architect of the study.

"This is bad news for birds like the Whitethroat, a common farmland bird. The added distance is a considerable threat.

"As temperatures rise and habitats change, birds will face their biggest challenge since the Pleistocene era, which ended 11,000 years ago”, he said in a statement.

Some 500 million birds migrate each year from Africa, some weighing as little as nine grammes (three-tenths of an ounce).

To complete a voyage that can be thousands of kilometres long, birds have to fatten themselves up to twice their normal weight. Some even shrink their internal organs to become more fuel efficient, so any additional distance travelled takes its toll.

The study is published in the Journal of Biogeography. From 2071 to 2100, nine out of 17 species examined are projected to face longer migrations, particularly birds that cross the Sahara desert, the study found.

Some birds traverse the Sahara and the Mediterranean Sea in a one go, while others make a pit-stop in northern Africa before crossing. Many fly at night, when temperatures are cooler.

A few -- such as the Blackcap -- have started to adapt by spending winters in Britain, but such behaviour remains exceptional, the study said.

The study forecast that the migration distance of the Orphean Warbler will jump from 2,700 kilometres (1,700 miles) to between 3,050 and 3,350 kilometres (1,900 and 2100 miles), with even longer increases for the Subalpine and Barred Warblers.

(Agencies)