It’s not hard to tell which people in a train station have just travelled across the world: they are the ones wearing hats because their hair is a mess. Long-distance migratory birds like the red knot Calidris canutus also have a tough job looking good - and appearance is important, because having reached their arctic breeding grounds, they need feathers preened to perfection to be attractive to potential mates. But, as if the non-stop 5000km flight wasn’t enough to guarantee the avian equivalent of a bad hair day
Preening keeps plumage in top condition, and ‘preen wax’, secreted by a special gland, is the vital ingredient. In the warmth of the southern feeding grounds, this wax is thin and easily applied with the beak - but in the Arctic, the lower temperature makes the wax thicker, and high quality preening becomes a difficult task. To their surprise, Theunis Piersma and colleagues from The Netherlands Institute for Sea Research found that when the birds migrate, instead of producing thinner wax to counteract th
The researchers suggest that this seemingly backward change has evolved to give a reliable cue for choosing a mate. Heavily waxed feathers mean better plumage-shine during the all-important breeding season, but due to the added preening difficulty, only the strongest and most skilful birds are able to look their best.
(Ecology Letters vol.2, p201-3) Richard Northover