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((long-tailed finches))
Many animals go to considerable lengths to make it obvious whether they are male or female, but in some species, such as the Australian long-tailed finch Poephila acuticauda, the sexes are completely indist hinguishable - a male has to perform a courtship display to show a female that he is of the opposite sex. This would seem to be a waste of time when he could simply rely on permanent signals such as coloured plumage so why be so secretive?
Naomi Langmore and Andrew Bennett of Cambridge and Bristol Universities respectively found that if a lone male finch is confronted with a group of unfamiliar birds, he is unlikely to advertise his sex by displaying. There is a 'pecking order' among males, and high-ranking individuals can be aggressive towards their inferiors. So, to avoid getting picked on, males keep their sex hidden.
Meeting a single unfamiliar bird is a different matter - a male will give the game away by courting the stranger. A subordinate male cannot afford to conceal his identity all the time, otherwise he will never find a mate. When confronted w ith one bird, the risk is worth taking - the stranger might turn out to be a female. But when a number of birds are present, there is a high chance of a male being subordinate to one or more of them, so it is better to stay anonymous.
But what if a male is approached by a stranger who starts to court him? Should he reveal that he is a male, too? Not if it means being attacked, say the researchers - they found that if a male is courted by a higher-ranking individual, he keeps his identity secret, rather than provoke a fight that he is likely to lose.
(Proceedings of the Royal Society of London B, vol.266, p543-50). Richard Northover
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