Attractive birds are poor fliers

Birds with the brightest feathers may look stunningly attractive and sexy but they go on to become poor fliers, according to a new study.

Males with the brightest plumage are believed to be more sexually attractive to female birds.

But a new study of American goldfinches by Professor Kristen Navara of the University of Georgia in Athens, US and colleagues at Auburn University, Alabama, is the first to show that high levels of brightly coloured chemicals in feathers leads to a breakdown in flight muscles, which affects flight performance, reports the BBC.
 
The discovery does not necessarily mean that the brightest birds are also the weakest, or least able to reproduce.

Instead it shows that having bright feathers comes at a real cost to male birds.

As part of the research, Navara and colleagues studied what happened to American goldfinch birds fed a diet rich in carotenoids.

The beneficial effects of high levels of carotenoids are well documented by scientists: as antioxidants they are thought to improve bird's health, and the resulting bright feathers signal to female birds that males are healthy, have less parasites and a good diet.

But until now, scientists have not examined whether there is a downside to eating lots of carotenoids.

Over two consecutive seasons, the researchers fed wild caught goldfinches a high carotenoid diet for two months, followed by a normal diet for two months.

A control group of birds was consistently fed a diet low in carotenoids.

During the experiments, the researchers collected feathers from the birds to measure how much carotenoid pigment was taken up into the bird's plumage.

In the first year, they also tested for levels of an enzyme that might indicate muscle is being broken down in the birds.

In the second year, they followed this up by directly testing the bird's ability to fly by measuring the performance of the bird's flight muscles.

The results showed that birds fed carotenoid supplements were significantly more colourful, having more strikingly yellow feathers.

However, birds fed this high-carotenoid diet also produced high levels of muscle-wasting enzymes, as the carotenoids became toxic, causing tissue damage.

They also performed less well during flight tests.

The findings have been published in the journal Naturwissenschaften.