LOCOMOTOR MECHANISMS OF BIRDS 



By FRANK A. HARTMAN 



Department of Physiology 



The Ohio State University, Columbus, Ohio 



INTRODUCTION 



Ornithological literature abounds in descriptions of the habits and 

 activities of birds, while anatomical studies are less common and are 

 related mostly to taxonomy. Attempts to correlate structure with 

 function in birds are few, yet this is a very intriguing subject for 

 study since birds are among the most active members of the animal 

 kingdom. This is reflected in their high rate of metabolism and ele- 

 vated temperature. Their versatility is great; they can fly, run, or 

 swim, some performing all these activities, while others are limited 

 to one or two. However, certain species excel in locomotion in the air, 

 on the land, or in the water. 



We note the explosive flight of the grouse, the graceful glide of the 

 swallow, the soaring of the vulture, the poise of the hummingbird, the 

 racing of the roadrunner, and the diving of the loon. Their skill can 

 be seen, their speed can be measured, but the relative power involved 

 escapes us. 



Actual measurement of these activities is necessarily limited, since 

 the confinement required would defeat its goal, but the muscles can 

 be weighed as an indication of their potential capacity. The flight 

 muscles can serve as a measure of power in the air. Likewise muscles 

 of the lower extremities represent the power for terrestrial or aquatic 

 locomotion, while heart weights bear a direct relation to the ability to 

 sustain activity. The areas of the wings, tail, and total gliding surface 

 are measures of the airlift, and the relation of length to breadth of the 

 wing shows the adaptation for lift or glide. The superficial and deep 

 layers of the pectoralis, which constitute 48 to 68 percent of all flight 

 muscles, are most essential in depressing the wing or lifting the body, 

 while the supracoracoideus raises the wing. The remainder of the 

 flight muscles (grouped in the master list, table 1 (pp. 38-87), under 

 the heading "Rest") play their part in controlling wing movement. 



Little accurate information about the relative size of muscles has 

 been available. General statements have been made such as that by 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 143, NO. 1 



