Last week I wrote about snakes in Asia, and how they are evolving to take advantage of the local snails. This week it’s birds in Europe.

Blackcap warblers in central Europe have a genetically determined migration route that takes them to the Mediterranean when the weather cools in the fall. Well, it used to take them to Spain… now some populations go to England instead.

Why England? Bird feeders. People feed birds during the winter in England, and the birds evolved to take advantage of that. 30% of blackcap warblers now migrate to England.

Since food is readily available during the winter in England, and it’s a shorter route back to their summer home in Germany and Austria, the birds get to summer nesting sites earlier, and the English-winter birds mate with each other and not with the Spanish-winter birds.

This is called “reproductive isolation” and it’s one of the first steps in creating new species. The warblers are still the same species–they can still mate and produce fertile children–but they’re beginning to look different, fly differently, and eat a different diet.

More details, and some excellent photos here: Feeding Birds Could Create New Species.