AMERICAN DIPPER. Cinclus mexicanus unicolor Bonaparte

Field characters.—Body size nearly that of Robin, but tail very short, about one-half length of body. Whole plumage appearing dark slate gray; young paler toned beneath, with whitish throat. No contrasted markings anywhere in adults save for small white spot on upper eyelid; when perched on rock or bank, bird bobs body down and up at short intervals. (See pl. 52.) Voice: Male has an elaborate and varying song; call note a short zit or bzeet, given singly or in rapid series.

Occurrence.—Common in Transition, Canadian, and Hudsonian zones on both slopes of Sierra Nevada; resident at least up to Canadian. Recorded in summer from near Bower Cave and El Portal eastward to vicinity of Williams Butte. In winter appears down Merced River as far as Goff. Lives along swift-flowing streams. Solitary.

The Yosemite visitor who has read John Muir's splendid description of the Water Ouzel in The Mountains of California will be keen for a first-hand acquaintance with this most interesting and singular inhabitant of the Sierran creeks and rivers. But even without an introduction the American Dipper merits more than ordinary attention. It is the only one of our local species of 'song-birds' of land dwelling ancestry which has taken to, and has become specially adapted for, gaining a livelihood in and under the water.

The American Dipper lives along swift-flowing streams in the Transition, Canadian, and Hudsonian zones at altitudes of from 2000 to 10,000 feet, and it is continuously resident, even under the rigors of the Sierran winter, up as high as any water remains open. Streams which afford conditions suitable for trout are likely to be tenanted by the dipper, especially where there are cascades and where scattered rocks in mid-stream give appropriate resting places. Smooth water is less frequented by the bird. The dashing waters surrounding Happy Isles in the upper part of Yosemite Valley afford optimum conditions for the species.

Examination of a specimen of the dipper in hand shows several notable adaptations to an aquatic mode of life. The covering of feathers on the body is thicker and denser than in either the thrushes or wrens, to which the dipper is closely related. Also, the ends of the feathers are somewhat more loosely formed, as in many of the true water birds, and this seems to help in keeping the plumage from soaking up water. Each nostril is covered by a movable scale, obviously to exclude water when need be. The oil gland at the upper base of the tail is about ten times as large in the dipper as in related land-dwelling birds of equivalent size, and the bird makes frequent use of the product of the gland to dress its feathers. The stout but tapered form of the body, the short tail, the short rounded wings, and the stout legs and feet all would seem to be of advantage to a bird living along and in swiftly moving waters. The nictitating membrane or third eyelid is whitish in the Dipper, and, when drawn backward across the eye, as it is frequently when the bird is above the water, can be seen at a considerable distance. This membrane probably is drawn over the eyeball when the bird is working beneath the surface of the water.

A notable feature in the behavior of the dipper is the frequent bobbing or squatting movement of its body, down and up; hence the name. Such a movement is often the first feature of a bird to catch the observer's eye and it always forms a ready aid in identifying the species. The rock and cañon wrens have a similar movement; but the purpose of this dipping in any of these birds is not known. One dipper seen standing on the margin of the ice in the river in Yosemite Valley, December 22 (1914), was bobbing upon one leg; the other leg was presumably drawn up into its plumage.

The dipper forages along the shore, on rocks in the stream (pl. 52), and on the bottom of the stream beneath the running water. When hunting along the shore the bird moves by short hops, turning to one side and the other, and bobbing its hinder parts almost incessantly. If the shore line be interrupted by a small embayment of quieter water the bird may swim across on the surface, or it may fly, holding its feet stretched forward and downward in readiness to alight when a suitable rock appears or the shore is again reached. When getting food beneath the surface, the dipper dives directly into the stream, usually against the current, and then seemingly walks along the bottom, the wings assisting. As it walks along it searches the crevices between rocks and the submerged surfaces of boulders where are to be found the larvae of certain insects which it seizes and devours. Near El Portal, one day in December, a dipper was seen to plunge head first into the rushing Merced River, to reappear about twenty seconds later some fifteen feet up the stream. Upon emerging, a shrug or two of the body rid the plumage of most of the adhering water. In summer, after the young leave the nest and before they are able to live independently, they perch on rocks along the shore while the parents hunt and dive in search of food for them.

The song of the American Dipper is given throughout most of the year, perhaps more frequently during the winter time than in summer. We have heard it many times in the fall and winter months at El Portal and in Yosemite Valley. Certainly it comes more often to attention in these seasons when most other birds are quiet and when the rush of the rivers and booming of the Valley falls are stilled. On December 22, 1914, several of the birds were playing about the river ice in Yosemite Valley and giving voice to numerous calls; on March 1, 1916, while snow was falling heavily in the Valley, a dipper was heard in full song.

The utterance is not easily transcribed, being varied as to both theme and rendering. Some passages suggest comparison with notes of the California Thrasher, some with those of the mockingbird, and others with certain wren notes; but there is a distinctive quality to the dipper's song which makes direct comparison misleading. Perhaps part of the impressiveness of the song comes from the surroundings amid which it is heard, but certain of its pleasurable features are assuredly intrinsic.

The call note is short and rather burred, uttered singly when the dipper is 'jouncing' on a rock, or given in rapid series when the bird takes to flight. One of our renderings of it is zit, zit, zit, . . .; another bzeet, or extended to bz-ze-ze-ze-ze-ze-et. It is quite different in character from the song, and resembles in general character the call note of the cañon wren.

The American Dipper nests amid the surroundings which harbor it throughout the year, placing the structure on a rock close to or over rushing water where the surface of the nest will be kept wet by spray. Interiorly the nest is much like that of a cañon wren, but its outer walls consist of moss which, being continually moistened, remains green throughout the period of occupancy. The entrance is at the side, so that the whole structure is oven-like. Occasionally the nest is placed under a waterfall and only comes to view upon the cessation of the flow in the autumn. In former years a pair of dippers nested on the stone abutments to the old bridge near the Sentinel Hotel, but replacement of the structure by a new one of modern type, with smooth-finished surfaces, left no place for the birds; in 1919 no dippers were to be found in that vicinity.

On May 10 (1916) a nest containing five birds about five days old was seen on a beam under the bridge over Rush Creek, southeast of Williams Butte. A two-thirds grown youngster was being fed by an adult on May 26 (1911), in Yosemite Valley near the Sentinel Hotel. A young dipper already able to live independently was seen on Indian Cañon creek in Yosemite Valley on July 6 (1915). These dates indicate a nesting season continuing at least from April until the end of June.

In winter months dippers appear on the Merced River below El Portal and then range westward at least to Goff. They are to be seen readily from passing trains. Whether these are birds forced down from the ice-bound streams of the high Sierras or are migrants from farther north is not known.