NO. I LOCOMOTOR MECHANISMS OF BIRDS — HARTMAN 5 



and in Tinamus, where the submergence may reach 9 to 10 mm. The 

 wings are small (buoyancy index, 2.86 to 3.14) and broad (aspect 

 ratio, 1.49 to 1.62). The wing area per gram of flight muscles is 

 19 cm. 2 in Tinamus and 36 cm. 2 in Crypturellus. Nothocercus 

 possesses smaller pectoralis muscles (P<o.oi) but larger lower- 

 extremity muscles than Tinamus and Crypturellus. The muscles are 

 in keeping with the habits — these birds run along the ground or fly 

 explosively for short distances, the small heart preventing more 

 prolonged effort. 



Podicipedidae. — Grebes are most proficient in swimming and 

 diving, using their feet in the process (Van Tyne and Berger, 1959). 

 Their flight muscles are very small, being only 14 percent of the body 

 in Podiceps dominicus. This species, which weighs only a little more 

 than one-third as much as Podilymbus podiceps, possesses almost 

 double the wing area of the latter. Podiceps dominicus also has a 

 lower aspect ratio (2.51 compared to 2.91). The tails are insignificant 

 in both species. The leg muscles are large, being 16 percent in 

 Podiceps and 18 percent in Podilymbus. The leg position is ideal for 

 swimming but causes an awkward waddling gait in walking. The 

 heart is moderate in size in both species (1.00 to 1.05 percent). 



Pelecanidae. — The clownish brown pelican starts rather awkwardly 

 with slow, sweeping wing strokes, continuing with frequent soaring and 

 sailing or, on a gentle breeze, gliding gracefully just above the water. 

 The male has relatively larger flight and leg muscles than does the 

 female, but compared to the cormorant, the flight muscles are but a 

 little larger while the legs are less than half the size. His wings are 

 moderately large (1.34 cm. 2 per g. of body; buoyancy index, 4.38) but 

 very long (aspect ratio, 3.75), enabling him to skim over the water 

 with ease. 



Phalacrocoracidae. — The cormorant prefers to dive and swim, 

 since that is his method of obtaining food. He is a rapid swimmer, 

 using only his feet according to Selous (see Bent, 1922), holding his 

 wings motionless. In the air he is a heavy flier (flight muscles, 17 per- 

 cent; buoyancy index, 3.27), slowly flapping his wings after the 

 manner of a heron. His legs are large (muscles are 11 percent of 

 the body), but because of their position, on land he is awkward, 

 though less helpless than the grebe. 



Anhingidae. — The anhinga, like the cormorant, obtains his food 

 by diving and swimming, using his feet only, with wings slightly 

 folded or slightly expanded and steering with his tail, which can be 

 spread as a rudder (Bent, 1922). However, unlike the cormorant he 



