Cormorants and some other seabirds can dive to a depth 30 metres, but their protective feathers remain dry. Recently, researchers at the Massachusetts Institute of Technology (MIT) examined how the birds did it. They published their research in the Journal of the Royal Society Interface.
According to MIT news,
“It had been known that during dives, a thin insulating layer of air called a ‘plastron’ is trapped by the feathers, meaning that water never comes into direct contact with the skin below the feathers. The team’s analysis now shows that beyond a depth of a few meters — far less than the depth these birds can reach — that plastron collapses, allowing water to penetrate into the feather structures. ‘It’s an abrupt transition,’ says Cohen, the Raymond A. and Helen E. St. Laurent Professor of Chemical Engineering.”
There’s more to it, however:
“But even after the collapse of the protective air layer, the preen oil changes the energy required to fully wet the feather’s barbs and barbules: In short, the wetting is reversible.”