The friendly bird-feeder could be an evolutionary force to be reckoned with. British people who feed birds are contributing to the evolution of a whole new species of blackcap, new research suggests.
at the University of Freiburg in Germany and colleagues measured genetic variation between blackcaps in two German sites 800 kilometres apart just after the birds had returned from their winter grounds on the Iberian peninsula and in the UK, respectively.
Both groups return annually to the same forest in Germany, where they live for six months of the year. Fifty years ago, most German blackcaps flew south to Spain or Portugal for the winter. But since the 1960s, a growing number of the birds have started migrating to the UK.
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Fed up
To their surprise, the team found that blackcaps that spend winter in Spain share more genes with those that live 800 kilometres away but also overwinter in Spain than they do with blackcaps that live in the same forests but overwinter in the UK. This suggests that despite living side-by-side for half of the year, the birds no longer breed together.
鈥淎fter world war two, the British started to put out far more food for the birds than they did before,鈥� Schaefer says. 鈥淎s a result, those that accidentally migrated north thrived rather than being killed off, leading to the evolution of a whole new lineage.鈥�
鈥淭his may be the first example of human behaviour generating a new ecotype or lineage of an animal,鈥� says of the Edward Grey Institute at the Department of Zoology at the University of Oxford in the UK.
Skinny beak
Schaefer鈥檚 team also found that German blackcaps wintering in the UK possess browner plumage on their backs, rounder wings and pointier beaks than blackcaps that migrate south.
鈥淭he bird food that the blackcaps rely upon in Britain is powdered, so there is no longer selection for the broad beaks that allow the bird to eat large fruits such as olives on the Iberian Peninsula,鈥� says Schaefer.
He says the two migrating populations are less likely to breed together because those that overwinter in the UK return to Germany earlier than those that go to Spain.
Journal reference: (DOI: 10.1016/j.cub.2009.10.061)