"Long distance migratory birds -- those that spend the winter in tropical Africa -- seem to be particularly late in leaving this autumn," the League for the Protection of Birds said in a statement.

The league's network of birdwatchers have spotted swallows all over France, including in the north, as well as warblers, which usually leave in August or September.

"This phenomenon is just another sign that we are seeing rapid and major climate changes that the birds are having to face, especially the migrators," it said.