Feather colour may reveal survival strategy in birds

London, Jan 30 (ANI): Researchers in France have shown that the colour of a bird's feathers indicates the strategy its immune system uses to beat pathogens.

Previously, pigments in feathers have been linked to the overall health of birds, reports Nature.

The carotenoids that give the blue-footed booby's feet their distinctive colour, for example, are also antioxidants that are found in its food. So a booby that is suffering from infection or starvation will have less colourful feet than a healthy bird.

And now lead-author Julien Gasparini of the Laboratory of Ecology and Evolution at the Pierre and Marie Curie University in Paris, and his colleagues have shown that female tawny owls (Strix aluco) with dark red plumage mount a more powerful response to infection than females with lighter feathers.

However, this stronger response comes at a cost - darker females lost more weight over the course of the study than pale females.

The findings suggest that females are advertising their immune strategy with their colour, rather than advertising overall health.

Carotenoids only account for a small percentage of colouration. Melanin, another pigment, is very common and is often involved in camouflage colouration.

Gasparini and his colleagues decided to study the role of melanin in wild tawny owls. They collected feathers from 102 egg-laying tawny owls, digitally photographed them, and used software to analyse their colour.

They repeated the experiment on the 258 chicks that later hatched and found that colour was heritable. The researchers then vaccinated roughly half of the adults with a cocktail of antigens from diseases such as tetanus and diphtheria.

Between 6 and 38 days later, birds were recaptured and weighed, and samples of their blood analysed for antibodies to determine the strength of the immune response.

The researchers found that the degree of red in a female's feathers is closely linked to the amount of antibody that she produced against the vaccines, with dark red females maintaining a higher level of antibodies for a longer period than paler females.

Whether melanin is linked to the immune strategies of all birds in this way is not yet known. But, the researchers suggest that colour could be signalling the presence of metabolic traits that would otherwise remain invisible.

The study is published in the Journal of Animal Ecology. (ANI)