Adapted from Jim Conrad's online book A Birding Trip through Mexico, This excerpt from "The Oak-Pine Forest of Bahuichivo"
in western Chihuahua state
Just opposite to the secretive, silent manner of trogons, all day long, up and down the middle of the stream, shrilly calling with excited-sounding trills and musical runs, two American Dippers fly low over the water very often passing right by my sitting rock. Related to thrushes and wrens, only four dipper species exist in the whole world, though dippers as a group are found throughout much of the Earth's uplands. They all have the same roundish, short-tailed, long-legged shape and all live along mountain streams with cool or cold, clear, flowing water. And the ones I've seen always struck me as irrepressibly hyperactive.
Dippers eat aquatic larvae of insects, especially those of beetles and caddisflies, and moths, snails, small fish, and fish eggs. Not only do they work along the water's edge like sandpipers, they also float atop water like ducks, and, incredibly, "fly" underwater, and walk along the stream's floor as they forage. They can fly from below the water's surface into the air, and visa versa, almost as if they simply don't recognize the boundary between water and air.
Underwater, a movable membrane over the nostrils keeps water out. When operating abovewater but in the spray of a waterfall, another membrane, the "nictitating membrane," slides over their eyes. Since the water in mountain streams is often very cold, the dipper's plumage is well insulated with a thick undercoat of down. Dippers have preen glands about ten times the size of any other songbird (ducks aren't songbirds), which provide the oil used for waterproofing their plumage during preening.