Nine out of ten female zebra finches prefer males with the reddest beaks, according to new research findings. But the attraction is more than skin deep. Not only are these males more attractive, they are also healthier.

The study, led by Dr Jonathan Blount of the University of Glasgow, is featured in the latest issue of Science (published 4 April) and was funded by the Natural Environment Research Council.

Dr Blount's team set out to discover why the more colourful males had the most luck with the ladies. Their research has shown that these males have far better immune systems than finches with less extravagant displays of colour. So picky females are more likely to get a healthier mate as well as a better-looking one.

The scientists varied the food intake of carotenoid pigments in a group of brother finches. Carotenoids are naturally occurring nutrients responsible for the yellow and orange coloration patterns in animals and in food: for example, the orange in a carrot. They measured the effects on beak colour, sexual attractiveness and the immune system. They found that the male zebra finches that ate more carotenoids developed redder beaks and became more sexually attractive to the females. These males also had substantially enhanced immune defences.

'Carotenoids are more than just colourful pigments - they are used in the body to neutralise harmful free radicals and to stimulate the immune system,' explains Dr Blount. 'Until now, it hasn't been clear whether all birds have sufficient carotenoids to maintain their sexual attractiveness and, at the same time, keep their immune system in top working order. Our research suggests that this isn't the case: 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.'

A number of additional factors are known to influence the ability of animals to obtain dietary carotenoids and to use them to enhance sexual displays. These include foraging efficiency, the effects of parasites in the digestive tract and the amount of energy needed to convert the carotenoids into a usable form.

Dr Blount adds, 'While beak colour is not the only signal female zebra finches consider when selecting a mate, it's now clear that a male's carotenoid levels, and therefore attractiveness, are linked to the effectiveness of his immune function.'

Given that carotenoids are found in a variety of foods, maybe men should start investing more in carrots and cabbage and less in flashy cars and designer gear...

Media Relations Office (media@gla.ac.uk)

Dr. Jonathan Blount, University of Glasgow, leads the research for this study. Others in the research team are: Neil Metcalfe, University of Glasgow, Tim Birkhead, University of Sheffield, and Peter Surai, Scottish Agricultural College.

NERC leads in providing independent research and training in the environmental sciences. See www.nerc.ac.uk for information.

For more information contact:

Dr Jonathan Blount, University of Glasgow, tel. 0141 330 4954,

Judith Hodgson, Press Officer, University of Glasgow, tel. 0141 330 3535 / 3683

Marion O?Sullivan, Press Officer, NERC, tel. 01793 411727.

Images of the zebra finches are available from the University Press Office. Any use of these images must be credited to Tim Birkhead.

Dr Blount will be available for interview

First published: 4 April 2003