Birds
American Dipper
Cinclus mexicanus · also called water ouzel
Watch a rushing mountain stream in the western United States for long enough and you may see a plump grey bird land on a mid-current boulder, bob up and down a few times, and then walk straight into the water and disappear. It is the American dipper, the only songbird on the continent that swims.
Overview
Cinclus mexicanus lives along clear, cold, fast streams in the mountains of western North America, from Alaska to Panama. It is a compact, slate-grey, wren-shaped bird that feeds on aquatic insect larvae, small fish, and fish eggs gathered underwater.
Swimming songbird
It walks along the stream bed gripping the rocks and swims with half-open wings against the current. It has the largest preen gland of any songbird, a dense downy coat, nostril flaps, a transparent third eyelid, and blood that carries extra oxygen, all of which let it forage in near-freezing water through winter.
The bob, and the nest
It bobs its whole body constantly on a perch, for reasons still debated. Its domed moss nest is built on a ledge or bridge girder, often right behind a waterfall.
Status
Least Concern and stable, but tied absolutely to clean, cold, fast water — which makes a breeding dipper one of the best signs that a stream is healthy.
American Dipper: common questions
How does a small songbird walk underwater without floating up?
It works against its own buoyancy. A dipper entering fast water angles its body and wings so the current pushes it down onto the stream bed, and it uses its strong legs and long claws to grip the rocks and walk upstream against the flow, head down, flipping stones to find larvae. In deeper or slower water it swims, beating its half-open wings like flippers to fly through the water. It can stay under for several seconds at a time and pops back to the surface like a cork when it stops swimming. The dense, heavily oiled plumage traps air and keeps the bird warm and dry to the skin.
Why does the dipper bob up and down all the time?
Nobody is completely sure, and several explanations probably each hold part of the answer. The rhythmic dipping may help the bird gauge the distance and speed of prey and rocks against the constantly moving background of the water, a bit like a person swaying their head to judge depth. It may also be a visual signal to mates and rivals that carries better than sound in a noisy stream environment, since the bob is often exaggerated during encounters. And it may simply be linked to the bird's readiness to dive. The habit is strong enough that it gave the bird its name.
What is a water ouzel?
It is an old name for the same bird. Ouzel is an archaic English word for a blackbird or a blackbird-like bird, and early naturalists and writers, including John Muir, who wrote a famous essay about it, called this species the water ouzel because of its dark, rounded, thrush-like shape and its association with mountain streams. American dipper is the standard name now, but water ouzel still turns up in older books and in place names. The four dipper species worldwide are the only members of an otherwise entirely land-based songbird order that have taken up an aquatic life.
Is the American dipper a good sign for a stream?
A very good one. Dippers need cold, clear, fast, richly oxygenated water with a rocky bed and a healthy population of aquatic insect larvae, and they will not persist where any of that is missing. A stream with resident, breeding dippers is almost certainly clean and biologically healthy. Conversely, dippers disappearing from a stretch of river is an early warning of siltation from logging or construction, pollution, acidification, or the loss of flow and cold water below a dam. Biologists use their presence and breeding success as a practical measure of stream condition.