Animal populations that include showy males are at higher risk of local extinction
A peacock. There may be a decrease in genetic diversity as most females mate with a handful of attractive males
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Showiness has a price, at least in the bird world. For decades, biologists have speculated that the loud plumage of the males in many species of birds comes at some cost. According to the accepted explanation for the evolution of the colorful feathers, the flamboyant male signals to the females, in a way that cannot be faked, that he is healthy. And according to a long series of studies, the lives of showy males are indeed more dangerous and shorter.
But according to a new study, published in the journal "Academy of Sciences, "Proceedings of the National, it's not just the males who pay the price of the magnificent display. Populations that include showy males seem to be at a higher risk of local extinction than groups where the males are more modest.
Paul Doherty of Colorado State University and his colleagues studied the changes that occurred in bird populations in the United States and southern Canada for about 21 years, from 1975 to 1996. They used information from the "North American Bird Breeding Survey" (BBS), conducted annually by the Army of volunteer birders, traveling along predetermined routes, stopping at certain points and documenting all the bird species they manage to locate.
Doherty and his team looked at the information obtained in the BBS survey to find out what changes had occurred in the populations of certain species over the years. They selected 153 species, in which males and females have different colored feathers (in such cases the males are always the more colorful species); and 185 species in which the feathers of the males and females are identical - at least to the human eye.
The BBS observers record the information revealed to their eyes at each site for only three minutes, and the apparent absence of a certain bird species from that site in this limited period of time does not mean that the bird is not there. It is also possible that the colorful birds are easier to spot than the less bright ones. It is therefore necessary to use statistical methods to correct the distortions and accurately assess how often the reported absence of a particular bird species indicates the true flock.
After the statistical weighting, it became clear to the researchers that the risk of extinction of populations of bird species in which the males are colorful is 23% higher than that of populations of more modest species. The reason for this is still unclear. The fact that the colorful males are in danger as individuals does not have to harm the survival chances of the entire population - mainly because the male's contribution to raising the offspring is small, as is often the case with birds of this type, where there is a formal difference between the two sexes. One possibility is that the decrease in genetic diversity, which occurs when most females mate with a handful of attractive males, means that the entire population becomes more vulnerable to disease.
The good news for the birds is that the local extinction caused in this way is usually temporary. Ecological niches that are emptied due to such extinctions are filled by animals that reach them from other places. The bad news, Doherty fears, is that as the natural environment becomes more fragmented by human activity, the restoration process may be delayed. Dull feathers may, then, turn out to be an appropriate response to human intervention.
Economist
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