Scientists discover how birds evolved to have colourful feathers

A new study has opened a door into discovering how birds evolved to have dazzling arrays of colourful plumage.

Iridescence is responsible for some of the most striking visual displays in the animal kingdom, and a new study of feathers from almost 100 modern bird species is helping to uncover how this colour diversity evolved.

The phenomena of iridescence is when an object’s colour changes when it is viewed from different angles.

A team of University of Bristol researchers used electron microscopes to study extracts of the feathers of 97 species of modern birds with iridescent plumage, taken from the collections of the Zoological Museum of Copenhagen.

Researchers found colourful feathers contain the most varied melanosome forms of all types of birds including ones which are hollow or flattened or both, unlike black, grey and brown feathers that always contain solid melanosomes.

A melanosome’s shape together with the thickness of the protein layer of keratin determines the colour that is produced.

A glossy swiftlet in Malaysia
A glossy swiftlet in Malaysia

The new study is the first time melanosome variation in iridescent feathers has been analysed on a large scale, previously having been used to predict colour in fossil animals.

Dr Jakob Vinther, co-author of the study and a leading researcher in the field of paleocolour at Bristol’s School of Biological Sciences, said the new research meant scientists could look at fossils of prehistoric birds and see how their melanosomes had changed over the ages.

He added: “This demonstrates how we now have the tools to map out the evolution of iridescence in fossil lineages.

“It opens the door to many new discoveries of dazzling displays in fossil birds and other dinosaurs.”

The researchers sampled Scaniacypselus, a relation of the modern tree swifts, and Primotrogon, ancestor to modern trogons, to see if their 48-million-year-old ancestors also had iridescent plumage.

A Scaniacypselus fossil close up
A Scaniacypselus fossil close up

The model predicted that Primotrogon probably was iridescent, but it used solid rather than hollow melanosomes, unlike its modern descendants.

Lead author Klara Norden, who conducted the study during her undergraduate years at Bristol’s School of Earth Sciences, said: “It is already known that structural coloration is responsible for 70% of the colour variability in birds.

“These two facts might be coupled – birds evolved varied forms of melanosomes to achieve ever greater diversity in colour.

“I wanted to find out if we could improve current predictive models for fossil colour based on melanosome morphology by including all types of melanosomes found in iridescent feathers.”