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Oops. New feathers turn out lousy

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10:01am, August 28, 2001
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Going to the trouble of molting doesn't really get rid of a bird's lice after all. Furthermore, flying doesn't blow off tough lice–unless a bird wears nail polish. Thus go the latest bulletins from the dramatic war between bird and louse.

Brett Moyer of the University of Utah in Salt Lake City and his colleagues are upsetting the conventional wisdom about molting. When a bird sheds feathers and grows new ones, part of the reward comes from ditching parasites, researchers have assumed.

At first, the assumption seemed to hold up in Moyer's inspections. He and his colleagues saw significantly fewer lice on pigeons after a molt than before.

When the researchers counted lice by washing them off the pigeons, however, the difference in lousiness disappeared.

So, where had all the lice been hiding on the newly molted pigeons? During a molt, Moyer found, pigeons' lice squeeze down into the sheaths of developing feathers. Also, after the molt, the lush new plumage makes lice hard to find.

Lice that frequent the wing feathers of pigeons and other doves keep their grip when the birds take flight by hunkering down in a feather. The lice hide between the barbs sprouting from the central shaft, reports Moyer's Utah colleague Sarah Al-Tamimi.

To investigate why lice don't fall off, she checked the wings of tethered pigeons before and after they flew the length of a football field. When she altered the feathers so the lice that were a bit too plump to fit between the barbs, she found that the lice kept their grip. The snug match between louse and feather may help explain why lice remain so specific to hosts, says Al-Tamimi. So, she wondered how they'd held on.

In the troughs between wing-feather barbs, tiny hooked filaments interlock. To see whether the lice were gripping these structures, Al-Tamimi partially filled some troughs with nail polish. When she flew these pigeons, significantly more lice slipped off than usual.

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