246 Townsend, Use of Wings and Feet by Diving Birds. [julv 



under water is a help and not a hindrance. Experiments on 

 captive birds in tanks might determine these facts. 



That Loons are able to progress faster under water than on the 

 surface I have concluded from such observations as the following 

 (26): "Thus on one occasion I was watching a Loon swimming 

 about, dipping his head under water from time to time on the 

 lookout for food. The cry of another Loon was heard at a dis- 

 tance and my friend immediately dove in the direction of the other, 

 and, appearing on the surface for a moment, dove again and again 

 until he reached his companion. At another time on the Maine 

 Coast while watching a flock of young Red-breasted Mergansers 

 swimming off the shore, I noticed a movement as of a large fish 

 on the water outside. The Mergansers at once flapped in alarm 

 along the surface of the water towards the shore where I was hidden, 

 and I soon saw that a Loon was chasing them, following them 

 under water." Theoretically a Loon should be able to go faster 

 under water than on the surface, for on the surface the bird is 

 retarded by the waves in front and the eddies behind, and the 

 faster it goes the more it is retarded by these factors. The subject 

 of the resistance of submerged bodies has been exhaustively 

 studied by naval architects, and it has been shown that a prop- 

 erly shaped body completely submerged under ideal circum- 

 stances with the wave eliminated meets with little resistance 

 besides friction. The fact that a Loon when swimming rapidly 

 on the surface is apt to depress its body in the water so that its 

 back is awash seems to favor this contention. It may be argued 

 that the bird does this to avoid observation or to escape being shot, 

 but it certainly swims faster when thus submerged. Under water 

 the diving bird has a great advantage in being able to assume a 

 shape best adapted to cleaving the liquid medium. 



Incidentally it may be remarked that the Loon, in perfecting its 

 legs for use under water, has disabled itself for walking on the land, 

 but as it usually builds its nest on or close to the water, it can well 

 afford to sacrifice terrestrial locomotion. 



The combined use of wings and feet, a reptilian form of progres- 

 sion, would naturally be found among birds that had not fully 

 specialized in either direction. Among living birds the Cormorant 

 and the Penguin represent the extremes of specialization for the 



