Humans are inadvertently manipulating bird genetics by innocently providing birds with feeders in winter, according to findings by German researchers. Over less than 30 generations, birds visiting British and European gardens in winter have evolved different-shaped wings and beaks, the scientists say.
In time, they could eventually become a distinct species. The birds breed side-by-side in the same Central European forests, but began to follow different winter migration routes after some discovered rich pickings from humans in Britain.
Eventually they divided into two reproductively separate groups. One continued to fly south for the winter, migrating to Spain to forage for olives and other fruits. The other got into the habit of flying a shorter distance north-west to Britain, where bird-lovers fed them.
Despite being colder, this had the advantage of a ready supply of food from garden bird tables and feeders, and meant a quicker journey, according to the study published in the journal Current Biology. Dr Martin Schaefer, from the University of Freiburg in Germany, who led the study, said: “The new north-west migratory route is shorter and those birds feed on food provided by humans instead of fruits as the birds that migrate south-west do.
“As a consequence, birds migrating north-west have rounder wings, which provide better manoeuvrability but make them less suited for long-distance migration.”
They have also developed longer, narrower bills adapted to bird feeder food from pet shops and less suited to fruit-eating. “Our study documents the profound impact of human activities on the evolutionary trajectories of species,” said Dr Schaefer.
“It shows that we are influencing the fate not only of rare and endangered species, but also of the common ones that surround our daily lives.
“This is a nice example of the speed of evolution. It is something that we can see with our own eyes if we only look closely enough. It doesn’t have to take millions of years.”
Dr Schaefer thought it unlikely that the two groups of blackcaps would ever actually become separate species, because the habits of humans tended to change over time.
However, the findings showed the initial steps of speciation could occur very quickly in migratory birds.
Although blackcaps are mostly summer visitors, increasing numbers are now overwintering in northern Europe and Britain.
Experts believe both milder winters and an abundance of food have drawn the birds to northern Europe and Britain.
Wintering in the United Kingdom instead of Spain or Africa uses up less energy and allows the birds to return to their breeding grounds sooner.
