DIPPER 109 



lid. When the bird was in the shadow of the nest cavity, with my eyes within 18 

 inches of it, I could see the membrane very plainly as it frequently flashed across 

 the eye ball. * * * The true lids in most birds move up and down, the winker 

 moving horizontally. The Water Ouzel is an exception in so far as the move- 

 ment of the winker [nictitating membrane] is nearly vertical. In no bird can 

 the upper eyelid be made to close and open with the speed of the nictitating 

 membrane. According to the record made by the moving picture camera, there 

 are five frames, or individual pictures, impressed on the film at each flash of 

 the membrane. This represents about one-third of a second to each wink. 



* * * On one occasion Mr. Sandahl pressed the button of the camera exactly 

 at the time the bird winked. This picture shows the extent of the membrane's 

 action from above downward. It also shows the membrane as an oval cover- 

 ing of the eye and not a straight line as would be the case if made by the upper 

 eyelid. 



The membrane is called into action to clear the cornea of the watery mist 

 while the bird is near the spray and splashes of falls and rapids. This was 

 beautifully illustrated while the female was in the nest brooding. The flashes 

 of the membrane could plainly be seen. The spray from the nearby falls, with 

 the changing air currents could be seen to enter the nest and with each gust of 

 moistened air, the membrane was called into action with increased vigor to 

 brush aside the watery vapors from the cornea. This was performed independ- 

 ently of the white margined upper eyelid. The slow eyelid action is in part 

 controlled by volition ; the quick action of the membrane is brought about by an 

 unconscious reflex demand. 



Each pair of ouzels establishes and defends a definite territory on 

 its home stream, from which trespassing ouzels are driven. As a rule, 

 such territorial rights are respected, but sometimes the invading bird 

 is attacked and forced to retire. During the nesting season and when 

 broods of young have to be fed, such territories are quite extensive 

 and the nests are placed a mile or more apart ; Dr. Cordier thought it 

 unusual to find two nests within a mile. But when winter closes some 

 of the upper reaches of the mountain streams, the birds have to be- 

 come more concentrated at lower levels, and perhaps half a dozen birds 

 may be found within a mile or two. Dawson (1923) mentions find- 

 ing as many as 37 within a distance of two miles. Even then, though 

 the territories are shorter, they seem to be fairly well maintained. 



Voice. — The water ouzel is a beautiful singer, singing persistently 

 and almost constantly during most of the year and in all kinds of 

 weather. The song period is at its lowest ebb during the molting and 

 low-water period in August and September, but as soon as winter 

 snows have begun to replenish the mountain streams, early in winter, 

 it begins to build up and the flood tide of joyous music is reached 

 early in spring, mingling with the roar of rushing torrents, and 

 generally to be heard above the music of the cascades. John Muir 

 (1894) pays the following glowing tribute to the song of the ouzel: 



As soon as the winter clouds have bloomed, and the mountain treasuries are once 

 more replenished with snow, the voices of the streams and ouzels increase in 

 strength and richness until the flood season of early summer. Then the tor- 

 rents chant their noblest anthems, and then is the flood-time of our songster's 



