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Feather-Eating Bacteria Dulls Birds Plumage

August 3, 2009

Recent studies have shown that birds sporting brightly colored plumage are more susceptible to being infected with feather-eating bacterium, according to a BBC Earth report.

The bacterial infection can harm the birds’ health and cause their feathers to become dull.

The discovery comes from a study that found 99% of all Eastern bluebirds observed in the state of Virginia to be afflicted with feather-degrading bacteria.

Although this kind of bacteria was first found 10 years ago, the latest research has provided the best evidence to date that the bugs can, in fact, damage the health and color of birds.

“Feather-degrading bacteria are relatively new to ornithologists,” says Alex Gunderson of Duke University in Durham, North Carolina.

“The first report of their occurrence on wild birds was published only ten years ago,” he added.

Scientists have since discovered that the majority of wild bird species likely have at least one kind of feather-degrading bacteria hiding out in their plumage.

The bacteria works by hydrolyzing the beta-keratin protein, which accounts for over 90% of a feather’s mass.

These particular bugs are mostly found in a minority of birds sampled, and it has been difficult to determine the exact affect it has had on their hosts. 

This prompted Gunderson and colleagues Mark Forsyth and John Swaddle of the College of William and Mary in Williamsburg, Virginia to survey a population of Eastern bluebirds (Sialia sialis) living there.

They then discovered that 99% of all the birds observed were harboring feather-eating bugs, which was reported in the Journal of Avian Biology.

Even more interesting is the correlation found between the bacteria and the color vibrancy of the female birds’ feathers. They found that the brighter plumage contained more feather-dulling bacteria.

“This is some of the best evidence that bacteria are active on the feathers of live birds,” says Gunderson.

“The evidence is correlational, so there is a great deal more work that needs to be done to verify it.”

“But it does suggest that feather-degrading bacteria could be an important force influencing the ecology and evolution of birds,” he said.

But the bacteria didn’t appear to have a substantial affect on the color of male birds’ feathers, which is a rare example of a parasite ostensibly causing harm to one sex and not the other.

“I was surprised that the relationship with feather-degrading bacteria was different for males and females,” explains Gunderson.

“It is possible that, because males and females differ somewhat in where they spend their time, they could acquire different species of bacteria that have different effects. It is also possible that physiological differences between males and females result in different effects of bacteria.”

“This is complete speculation and at present we do not know the answer to this question.”

Other interesting and key results were found, such as the fact that the bacterial load also correlated with the condition of the bird’s body, which is directly related to their health and reproductive success.

The results broadly suggest that the feather-degrading bacteria may have a significantly adverse affect on the birds’ ecology.

The colors of a bird’s feathers serve to boast of their health, attract mates and even camouflage. Therefore, the dulling effect of the bacteria could even alter the evolution of bird color.

“If bacteria detrimentally influence feather coloration, they may place selective pressure on birds to evolve defenses against them,” says Gunderson.

“There is evidence that certain avian traits are defenses against feather-degrading bacteria. For instance, we know that feathers colored by melanin pigments are resistant to bacterial degradation, and that the preen oil that birds apply to their plumage inhibits the growth of some feather-degrading bacteria.”

“In general, an understanding of the influence of feather-degrading bacteria on birds could, to some degree, help explain the evolution of these and other avian traits,” he says.

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