A study of Eastern Bluebirds has found that in addition to the normal wear and tear on their feathers, they have to cope with feather-eating bacteria.
Feather-degrading bacteria work by hydrolysing the protein beta-keratin, which constitutes over 90% of a feather's mass.Birds are not entirely defenseless against these parasites:
But these bugs are usually found in a minority of birds sampled, and it has not been clear what impact they have on their hosts.
So Gunderson and colleagues Mark Forsyth and John Swaddle of the College of William and Mary in Williamsburg, Virginia, US surveyed a population of Eastern bluebirds (Sialia sialis) living in Virginia.
They found that 99% of all the birds surveyed carried feather-eating bugs, they report in the Journal of Avian Biology.
What's more, they found a correlation between the bacteria and the brightness of female birds' feathers, with more bacteria causing duller feathers.
"If bacteria detrimentally influence feather colouration, they may place selective pressure on birds to evolve defences against them," says Gunderson.I find this result very intriguing. The article focuses on sex differences: females suffer worse effects from the bacteria than males. I am also interested in the contrast between the infection rates found in this study compared to those in previous studies. Are bluebirds in general more susceptible to the bacteria than other bird species? Or does the bacteria spread more easily in Williamsburg than in other places?
"There is evidence that certain avian traits are defences against feather-degrading bacteria. For instance, we know that feathers coloured 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.