A tiny bird which has evolved into five different colour variations on a small tropical island prefers to mate with others of the same colour plumage, according to new research.

Dr Yann Bourgeois, of the University of Portsmouth, found that a DNA study of the grey white-eye, which lives on Reunion Island in the Indian Ocean, showed that the 4in (10cm) long songbird is likely to breed with similar mates.

He said both natural and sexual selection had led to colour differences in the varieties of the bird which lived in five distinct territories only a few miles apart.

Lowland brown variety of grey white-eye (Dr Yann Bourgeois/PA)

Dr Bourgeois said: “It surprised us that birds living just 10km (6.2 miles) apart already have differences in their DNA.

“Birds are usually seen as good dispersers, but these birds stay close to where they are born. Based on the results of this study, it’s possible they may be reproducing mostly with birds of the same colour.”

Highland brown variety of grey white-eye (Dr Yann Bourgeois/PA)

He added that hybrid birds which were the offspring from neighbouring territories might not breed successfully.

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Grey head brown variety of grey white-eye (Dr Yann Bourgeois/PA)

“It’s also known that big changes in altitude put a demand on all species – animals at higher altitude need more haemoglobin in their blood and tend to be bigger than their counterparts living closer to sea level, for example.

Grey variety of grey white-eye (Dr Yann Bourgeois/PA)

Dr Bourgeois added that he suspected that the birdsong of the different varieties of the island’s grey white-eye might have evolved a regional accent, such as has been found of birds in New Zealand, but research was needed to prove this.