Britain's enthusiasm for backyard bird-feeding may have led some of the nation's feathered friends to evolve bigger beaks in just the past 40 years, researchers said Thursday.

The report in the US journal Science compared beak length among birds known as great tits in Britain and The Netherlands, where bird-feeders are less common.

"Between the 1970s and the present day, beak length has got longer among the British birds. That's a really short time period in which to see this sort of difference emerging," said study co-author Jon Slate, professor in the department of animal and plant sciences at the University of Sheffield.

"We now know that this increase in beak length, and the difference in beak length between birds in Britain and mainland Europe, is down to genes that have evolved by natural selection."

The report is part of a long-term study under way on great tits in Britain's Wytham Woods, along with Oosterhout and Veluwe in the Netherlands.

Researchers screened DNA from more than 3,000 birds in order to uncover genetic differences between the British and the Dutch populations.

Changes in specific gene sequences in the British birds were found to closely match human genes that determine face shape.

Researchers also discovered that birds with genetic variants for longer beaks were more frequent visitors to feeders than birds without the genetic variation.

And there were "strong similarities with genes identified with beak shape," in line with naturalist Charles Darwin's historic study of finches, which showed how finches evolved physical traits that helped them adapt to different environments in the wild.

"In the UK we spend around twice as much on birdseed and bird feeders than mainland Europe -- and, we've been doing this for some time," said co-author Lewis Spurgin of the School of Biological Sciences at the University of East Anglia (UEA).

"Although we can't say definitively that bird feeders are responsible, it seems reasonable to suggest that the longer beaks amongst British great tits may have evolved as a response to this supplementary feeding."

Researchers on the study came from The Netherlands Institute of Ecology and the Universities of Wageningen, Oxford, Exeter, East Anglia, Sheffield.

Source: AFP