32 



diving birds we know nothing. Most of our observations on 

 their subsurface progression have been made with birds in 

 tanks, or just beneath the surface of the water. Ordinarily we 

 lose sight of them when they leave the surface, or immediately 

 afterwards. Usually under the most favorable conditions birds 

 cannot be seen plainly much farther below the surface than 15 

 or 20 feet. There are reasons for the belief that some of the 

 diving birds go to the bottom in more than 100 feet of water. 

 Thoreau l gives on the authority of the newspapers the state- 

 ment that a fisherman caught a Loon in Seneca Lake, New 

 York, 80 feet beneath the surface with hooks set for trout, and 

 says that Miss Cooper has made a similar statement. 2 



Bacon gives evidence that the Old-squaw when feeding in the 

 Great Lakes is taken in large numbers in gill nets at a depth 

 of 15 fathoms, and rarely at 27 fathoms (162 feet). 3 Mr. G. 

 Dallas Hanna of the University of California writes me that he 

 has taken freshly swallowed Crested Auklets from the stomachs 

 of codfish which were caught on the bottom in water 200 feet 

 deep, but this is not conclusive proof that the birds ever dive 

 to that depth. 4 



Probably in deep diving the bird must prepare itself for long 

 submersion by first filling the lungs with air. To force its 

 buoyant body to great depths must require extreme propulsive 

 efforts. By far the largest propelling surface about a bird is 

 that of the wings, and the pectoral muscles that give them 

 force are much the largest and most powerful in the bodies of 

 all flying birds. Therefore we may assume that if the pro- 

 pelling power of the wings can be directed backward, they must 

 give a greater impetus than that given by the feet. However, 

 we do not yet know how directly the wing power can be ap- 

 plied in diving. 



It seems probable that in deep diving the wings are always 

 used and probably the feet also. Dewar has timed diving birds. 

 He gives the time required to reach a certain depth and return 

 to the surface. The rule, he says, is twenty seconds for the 



1 Allen, Francis H.: Notes on New England Birds, by H. D. Thoreau, 1910, p. 5. 



2 Cooper, Susan Fennimore: Rural Hours, 1850, p. 10. 



s Bacon, Samuel E., Jr.: Ornithologist and Oologist, Vol. 17, March, 1892, p. 45. 

 4 There is much additional evidence, however, that diving birds reach a depth of more than 

 100 feet. 



