Birds' brighter colours linked to 'mating success'

The endangered hihi (stitchbird). Photo / APN

Birds of a feather flock together, and when it comes to sex appeal, brighter is often better.

A study, led by a New Zealand researcher, suggests a large proportion of birds have evolved to become more colourful over the past 56 million years.

The most likely reason? Sexiness.

And because being brightly coloured often makes a bird more attractive to females, many bird species may become more eye-catching as their evolution continues.

Massey University zoology lecturer Dr Daniel Thomas and colleagues from the US spent two years trawling through the data of close to 10,000 species of modern birds, nearly 3000 of which had plumage colours consistent with carotenoid pigments.

These pigments, which colour feathers red, orange, yellow, pink or purple, are found in almost half of living bird families, including the families that contain the robin, tomtit, stitchbird and yellowhead.

The study, published in the leading journal Proceedings of Royal Society B, covered all living birds.

Plumage carotenoids were found in a variety of species including ducks, storks and cuckoos, but parrots, penguins and some other species do not carry the pigments in feathers.

Dr Thomas said the suggestion that bright colours were attractive among birds had long existed in science.

"We can theorise about when these pigments first became sexy to birds, but we don't have fossil evidence of the behaviour. We do know, however, that breeding is a fundamental unit of evolution.

"So what the study is showing is that these colours have become more prolific over time, and really, the only way that could have happened if if they'd somehow been linked to mating success."

The study's "big take-away", he said, was just how widely distributed the particular type of pigment was - and how many different types of birds it was important to.

"It's huge - we found these colours in 40 per cent of all bird families, which adds up to around 3000 different birds."

Dr Thomas suspected if the trend continues, more and more species of bird would develop plumage carotenoids.

"It's not that individuals themselves would become brighter, but all birds as a whole would appear more colourful, because more and more species as a proportion would have plumage carotenoids."

For some species of birds though, factors such as camouflage would mean their feathers remain dull or cryptic.

"We know we are never going to get a flamingo-coloured nocturnal bird, as it would stand out in daylight while it was trying to hide and predators would eat it."