212 CURIOUS HOMES AND THEIR TENANTS. 



In places where the birds are sufficiently numer- 

 OUG they will take possession of a mountain stream 

 from its source to its mouth, each family occupying 

 about a quarter of a mile of its length, and never in- 

 truding on the domain of its neighbors. 



They are very quick and queer in their move- 

 ments, flying with a rapid buzzing of the wings, and 

 following closely every turn and elevation or depres- 

 sion in the level of the stream, until they drop sud- 

 denly and disappear beneath its surface. 



"When there is sufficient depth for a plunge," 

 says Prof. Nuttal, " they open their wings and drop 

 them with an agitated motion, and with the head 

 stretched out as in the ordinary act of flying in the 

 air, descend to the bottom, and there, as if on dry 

 land, course up and down in quest of food." 



Mr. Mudie observes, in regard to this : " A question 

 has been raised how the dipper can keep beneath a 

 fluid so much more dense than itself. An owl to an 

 owl's bulk of air is as eight pounds to one as com- 

 pared with the dipper's bulk of water to the dipper ; 

 but if birds ascend into the air at pleasure by the 

 motion of their wings, it is only reversing those mo- 

 tions to enable them to descend or keep themselves 

 down in the water. The difljerence in specific gravity 

 between the bird and the water is indeed so trifling 

 that very little effort is needed to move it in any di- 

 rection downward or sideways. 



" Birds do not fly because they weigh little, for 

 with equal wings the heavier birds fly best ; they do 

 so because they strike the air more forcibly in the op- 



