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The research group has shown how male birds with very red or orange
beaks are the ones that take in very high levels of nutrients, called carotenoids. Carotenoids are more than just colourful
pigments - they are used in the body to neutralise harmful free radicals and to
stimulate the immune system.
In their research, when they taxed the Blackbird immune systems - by
injecting sheep blood into the birds - their beak colour became less red due to
the decreasing amount of carotenoid in the beak.
Their report said "In Blackbirds, dynamic reallocations of
carotenoids from the beak to the immune system appear to convey a continual
update on male health. Reallocations of
carotenoids were observed in three weeks' time. We didn't think the response would
be so quick."
"Our research suggests that only those males with fewest parasites
and diseases are likely to be able to devote sufficient carotenoids to their
appearance to produce the best sexual display. While carotenoid-based beak colour is probably
not the only factor these birds consider when selecting a mate, it is now clear
that carotenoid levels are linked to sexual attractiveness and immune
function," said Professor Cézilly, Professor.
Such birds would have an advantage in the evolutionary
"marketplace". Animals with
stronger immune systems would naturally be better able to fight off disease. They may have more efficient physiologies, may
be better at finding nutritious foods, or both.
Their
conclusion was that female birds find males with the brightest beaks the most
attractive for good reason: these are also the healthiest birds.
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