An animal's attractiveness to potential mates is thought in some cases to be related to the animal's overall health and therefore suitability as a parent.
In few cases is health so clearly displayed as with the white spot on the flycatcher's forehead.
The size of the spot on a male flycatcher bird indicates his immune system's ability to fight off the avian flu virus, scientists announced Monday.
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The study found the male collared flycatcher can change the size of its forehead spot during mating season. Males that unfurl their forehead spots most are those that produce the most antibodies.
"It seems that the female uses the forehead spot as a health indicator," Mans Andersson of Uppsala University in Sweden. "When she chooses males with a large forehead spots, she takes not only the healthiest males, but also the ones with the best immune defense against future virus infections."
The birds are not magically transforming their spots. Instead, evolution is at work, allowing the birds to show off their health. The finding supports the theory that expression of secondary sexual traits, such as brighter plumage, bigger horns or a larger spot, signals traits that are beneficial for survival.
The finding is detailed in the journal Acta Zoologica.
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