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The Avian wing is an engineering marvel: lightweight yet incredibly strong, stiff yet flexible, forming an airfoil that instantly adapts to all conditions and, when not in use, folds into a thin panel and folds neatly to the side of the wing. the body of the bird. Understanding how the wing works and where the different groups of feathers go as the wing unfurls and folds is an important fundamental knowledge of bird identification. In this column, I will explain how the wing fits into the feathers of the body at rest.
The wing is made up of specialized flight feathers and covers, adapted to be stiff and flat to withstand the rigors of flight and create a good aerodynamic surface. They are not very good for insulation. This means that when the wing is folded to the side of the body, other feathers must keep the bird warm.
In my column for the August 2017 issue (“Avian Air Conditioning”), I described how songbirds use wing position to regulate their body temperature. In extremely cold weather, the flank feathers puff out from below, and the scapulars from above, so that these body feathers cover most of the wing and insulate the body.
Birds that spend a lot of time swimming face the added challenge of keeping water away from their bodies. Ducks and geese take wing storage to the next level: the wing is almost completely hidden at all times. In a swimming duck, the flank feathers curl to the sides to cover most of the wing, and the scapulars spread out to join the flank feathers. The only parts of the wing left exposed are the largest feathers visible towards the rear of the bird, usually a few large tertials (the innermost feathers of the wing) and the tips of the longest primaries. Everything else is hidden under the waterproof shell made of flank and scapular feathers. In a way, the duck rides in a “boat” of feathers: the long feathers of the sides extend above the waterline to form the gunwale. The scapulars are part of a canopy, and the folded wing simply folds inside.
In birdwatching, knowing what you can’t see is often helpful, and on a swimming duck, keep in mind that you’ll see very few wings.
This article from David Sibley’s ID Toolkit appeared in the May/June 2018 issue of BirdWatching.