544 ANIMAL LIFE IN THE YOSEMITE 



Occurrence. — Common in Transition, Canadian, and Hudsonian zones on both slopes 

 of Sierra Nevada; resident at least up to Canadian. Eecorded in summer from near 

 Bower Cave and El Portal eastward to vicinity of Williams Butte. In winter appears 

 down Merced Eiver 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 mil 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 Tran- 

 sition, 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 w^orking 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 



