for National Geographic News
For bird species whose males and females differ in color, guys with the brightest feathers tend to have the greatest lady luck. This natural mating game however puts entire local populations at risk of dying out, according to a new study.
The finding confirms the idea that the extraordinary lengths an animal will go to woo a mate, such as the peacock who spends time and energy to maintain his extravagant tail feathers, comes at a price in terms of survival.
"We found that to be true," said Paul Doherty, a wildlife ecologist at Colorado State University in Fort Collins who co-authored the study appearing in the current issue of Proceedings of the National Academy of Sciences.
This idea is a key component of the sexual selection theory put forth by Charles Darwin in 1871 to explain the evolutionary process that favors seemingly outlandish adaptations.
This behavior at first confused Darwin, who found such extravagant displays to fly in the face of natural selection in which the strongest survive. Traits such as bright feathers take time and energy to maintain and make the birds more vulnerable to predators.
Darwin's theory on sexual selection suggests the purpose of these traits is to allow a species to find a mate and thus pass on its genes to the next generation. In theory, this potential to carry one's genes forward outweighs the cost to individual longevity.
"Much of the theory of sexual selection depends on there being a cost, such that only the best individuals can display or have the best display," said Doherty. "Lesser-quality individuals either die or cannot bear the time or energy costs and get little reproductive success."
And, according to the study, although extravagant displays are costly in terms of extinction, bird species are able to make up for the loss of local population by quickly re-colonizing the area.
"You have species perhaps winking out more frequently, but at least in North American populations they seem to be coming back again by colonization events," said Jim Nichols, a study co-author with the U.S. Geological Survey Patuxent Wildlife Research Center in Laurel, Maryland.
Nils Chr. Stenseth and Glenn-Peter Saetre of the University of Oslo in Norway write in an accompanying perspective that the insight on bird populations gained from this study is "both novel and highly interesting from an ecological point of view."
Breeding Bird Survey
The study by Doherty and colleagues is based on statistical analysis of information recorded over the past 21 years by thousands of volunteers who participate in the North American Breeding Bird Survey, an annual bird count.
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