The icy stream runs fast and wide with snowmelt, its white water surface sparkling in the sunlight. Prismatic spray rises from the rapids. Into this maelstrom flies an American dipper, a stub-tailed bird about the size of a starling. The dipper alights momentarily on a mid-stream boulder, then dives into the torrent. After 15 seconds on the surging stream bottom, the bird bobs like a cork to the surface, precisely where it entered the water, and returns to the boulder. A juicy insect larva dangles from its bill. Just another dinner in dipper land.

American dippers occupy an unusual niche in the songbird world. Inextricably tied to racing streams, they routinely feed where few other terrestrial animals dare to go. They rear young just feet from churning whirlpools. They are splendidly adapted for their aquatic life-style, yet even in the wilderness have trouble finding appropriate nest sites. Ornithologists have long believed dippers to be too fragile to withstand human intrusion into their habitat, but new research by Montana biologist Sophie Osborn suggests otherwise. "Dippers appear to be able to withstand certain types of development," she says, "and the building of bridges may actually benefit them."

Formerly known as the water ouzel, this bird was rechristened by ornithologists several years ago because of its curious habit of dipping--bending and straightening its knees. Young birds may practice dipping while still in the nest, and adults do it repeatedly when resting between feeding dives, while courting, during territorial disputes and when alarmed. The dipping rate tends to rise with the degree of arousal to as many as 60 dips per minute.

Abundant oil from an oversized gland above the tail keeps dipper feathers virtually waterproof. A flap of skin covers the nostrils while submerged, and translucent eyelids permit underwater sight. Dippers rarely venture more than a few yards from water, and even when airborne they follow a stream´s zigzagging course. Like waterfowl (and unlike most other songbirds, which lose and replace feathers gradually), dippers compress the annual molt of their flight feathers to a week or two in August, during which time they may be unable to fly.

"They´re absolutely amazing," says Osborn. "I can´t even stand up in these streams, but here are these tiny birds that dive right into raging white water."

Facing into the current, a dipper plunges to the stream bottom, where its churning legs, long toes and thrusting wings help it remain long enough to find an insect larva or occasionally a small fish. This feat has been compared to cafeteria dining inside a washing machine.