quality:correction, structural:reformatting
Air sacs

Anatomical dissections of two brown pelicans in 1939 showed that pelicans have a network of air sacs under their skin situated across the ventral surface including the throat, breast, and undersides of the wings, as well as having air sacs in their bones. The air sacs are connected to the airways of the respiratory system, and the pelican can keep its air sacs inflated by closing its glottis, but how air sacs are inflated is not clear. The air sacs serve to keep the pelican remarkably buoyant in the water and may also cushion the impact of the pelican's body on the water surface when they dive from flight into water to catch fish. Superficial air sacs may also help to round body contours (especially over the abdomen, where surface protuberances may be caused by viscera changing size and position) to enable the overlying feathers to form more effective heat insulation and also to enable feathers to be held in position for good aerodynamics.