'It's also known that big changes in altitude put a demand on all species-animals at higher altitude need more hemoglobin in their blood and tend to be bigger than their counterparts living closer to sea level, for example. Bourgeois said: 'These birds don't like to cross anything barren.' The five separate grey white-eye birds' territories are bound by rivers or ancient lava flow streams, or by changes in altitude.ĭr. Reunion Island has a huge variety of landscape, with volcanoes, rainforests and beaches, but it is also very small, at about 50km long.

It's also possible that hybrids-the offspring of birds from neighboring territories-might not be as successful. Based on the results of this study, it's possible they may be reproducing mostly with birds of the same color.' 'Birds are usually seen as good dispersers, but these birds stay close to where they are born. Bourgeois said: 'It surprised us that birds living just 10km apart already have differences in their DNA. The study is published in Molecular Ecology.ĭr. Yann Bourgeois at the University of Portsmouth, found that natural or sexual selection have both driven differences in plumage color between territories that are only a few kilometers apart.

Scientists found distinct variations in patterns of grey and brown feathers in the 10cm-long songbird, called the grey white-eye, on Reunion Island, in the Indian Ocean.

Flock and feathers