From yellow to red

How have species of birds that were once yellow become red? This is a question that interests zoologist Staffan Andersson, who researches evolution in birds.

Researchers have always been fascinated by birds’ colourful plumage. Not only do many birds have colourful feathers, the also have what is perhaps the most advanced colour vision of all creatures on the planet. For example, they can see ultraviolet radiation that we can’t.

Staffan Andersson is a professor of ecological zoology at the Department of Biology and Environmental Science, and has studied birds and their colourings throughout his career. One of his early discoveries was that birds communicate using UV light when choosing partners and in connection with threat signals.
He conducted experiments with bluethroats in the Norwegian mountains in the 1990s, in which he captured male birds and “painted” their breast feathers with UV-absorbent sun cream. It turned out that the females preferred males whose UV radiation was intact.
“Since the change was only in UV and thus invisible to the human eye, this was the first evidence that UV is part of birds’ colour vision.”

HIS RESEARCH TEAM has also studied the colour signals of blue tits and great tits. Their plumage was measured using a special light meter, showing that male and female blue tits are not as similar as we UV-blind humans believe – the male’s cap is actually much brighter.
However, the birds that interest Professor Andersson most of all are the colourful African widowbirds. There are around twenty species with black plumage and tail feathers, and bright yellow or red patches of colour.
“Over evolutionary time, these species have developed from ancestors with short tails and yellow colouring into today’s species, some of which have extreme tail lengths and some are bright red. We want to find out how that has happened.”

Staffan Andersson

Staffan Andersson

THE FEMALES PREFER males with long tails, while the red colouring is a threat signal between males. Bright yellows and reds in birds are due to carotenoids, pigments and antioxidants that they ingest from grass seeds. It has long been known that certain birds can convert the carotenoid’s colour expression, but it has not been known how.
Professor Andersson’s research team has recently identified an enzyme that seems to be the key to these changes, which in itself is a major breakthrough.
“Understanding something so spectacular in nature’s diversity such as why some birds are red, some are yellow and some are blue – that’ll make me happier, at any rate.”

PROFESSOR ANDERSSON HASN’T always been obsessed with birds. As a teenager, it was larger animals and tropical environments that he was interested in, and he admits that he is part of the generation inspired by Swedish naturalist Jan Lindblad.
“Funnily enough, his Journey to Red Birds was one of the first books I read.”
He completed his thesis in the Swedish mountains, where he climbed precipices with a stuffed snowy owl on his back to study how rough-legged buzzards defended their nests.

His dream project now would be to solve the mystery of the widowbird, finding out what in the birds’ variety of colour signals is down to evolutionary history and genetic limitations, and what is down to selection and adaptation in the wild today. What is hereditary and what is environmental? The answer is, of course, an interaction of both. But how, exactly – that’s the question.
“Everything has a genetic foundation, and everything must have environmental input. The environment influences genes which open windows to other environmental factors, which in turn influence other genes. These mechanisms are highly significant in terms of nature’s rich diversity of colour and form.”