According to this article feeding the birds can affect the way that they evolve. Scientists have carried out a study on blackcaps which has found that they follow a different evolutionary path if they spend the winter eating food people have put out for them. The birds normal wintering ground is in southern Spain where they would feed on the fruit that grows there but some birds are now wintering in the UK because they can survive on the food we leave out on our bird tables. Studies have found that those birds which do this are now in the early stage of forming a new species. As the UK is closer to the birds breeding ground these birds also return early and claim the better territory than those that winter in Spain. The researcher found that the two groups of birds have different chemical signatures and have formed two distinct populations even down to the fact that they only mate within their own group. There are also differences emerging in the birds beak, wings and plumage with the birds that winter in the UK having rounder wings and longer narrower beaks more adapted to eating seeds and fat from bird feeders. It will be interesting to revisit this story in the future to see whether they have evolved further.