Thanks to bird lovers, the central European songbirds called blackcaps (Sylvia atricapilla) have split into two groups that may develop into separate species. So say Martin Schaefer at the University of Freiburg in Germany and his colleagues.
The researchers tracked the groups: one overwinters in the Mediterranean, where the birds feed on fruit; the other spends winter in the United Kingdom, where its members eat from bird feeders. The two groups return to nesting grounds in Germany and Austria at different times, and so tend to pick mates from among the birds that overwinter in the same place. The team found that, in less than 30 generations, the UK-wintering birds have developed distinct physical traits: rounder wings for their shorter migration and narrower beaks, which are less well adapted for fruit-eating.