Undertail
flickr.com
Sandhill Crane Not quite the ultimate in aerodynamic perfection - but just look at how he fairs his upper legs into the undertail coverts! He has to be forgiven for those feet, however. He has to use them for foraging, and thus makes the tradeoff. [EXIF: Canon 7D, 100-400mm, Av@f/11.0, 1/1000, Ev +1/2, ISO 800]