* Migratory birds face longer flights due to climate change
* Breeding grounds move north in Europe
* Biggest challenge to migrant birds since the Ice Age
By Alister Doyle, Environment Correspondent
OSLO, April 15 (Reuters) - Some European birds will have to fly further as global warming shifts their breeding grounds northwards in the biggest challenge to the tiny migrants since the Ice Age, scientists said on Wednesday.
Some types of warbler would have to add 400 kms (250 miles) to twice-yearly trips up to 6,000 kms to and from Africa, according to the report which said it was the first to examine the potential impact of climate change on avian migration.
"For some birds the extra distance might make the difference between being able to make it or not," Stephen Willis of Durham University told Reuters of the study he led with a team of British-based scientists.
The report, adding to projected threats to animals and plants from global warming, said an estimated 500 million birds migrate from Africa to Europe and Asia every year. Some weigh just 9 grams (0.3 ounces).
Nine of 17 warbler species studied would have to fly further under projected warming by 2071-2100, especially the whitethroat, the barred warbler or the Orphean warbler that cross the Sahara Desert, according to the study in the Journal of Biogeography.
"Some species may be able to adapt and change, for example by adopting shorter migration routes, if they can find enough food at the right time," Willis said in a statement. Some blackcap warblers in Germany had dropped winter flights south.
"As temperatures rise and habitats change, birds will face their biggest challenge since the Pleistocene era," he said.
The end of the last Ice Age 10,000 years ago marked the end of the Pleistocene.
The study said breeding grounds were moving northwards because of climate change, while wintering regions nearer the equator were less affected. The Arctic region is warming almost twice as fast as the rest of the globe.
The report, which also involved experts from Cambridge University and the Royal Society for the Protection of Birds, said the European Union should review protected areas for migrant species that need stopovers on their marathon flights.
Still, Willis said migratory birds had proved adaptable before -- surviving Ice Ages and the drying out of the once greener Sahara region about 6,000 years ago.
Willis said the scientists picked warblers because of their widely differing strategies.
Cyprus warblers, for instance, stay on the Mediterranean island year round and would be among those unaffected.
-- For Reuters latest environment blogs click on: blogs.reuters.com/environment/ (Reporting by Alister Doyle; Editing by Sophie Hares)