NO. I LOCOMOTOR MECHANISMS OF BIRDS — HARTMAN 31 



facialis is lower in nonflying or poor-flying birds than in long-distance 

 fliers such as the parakeet, pigeon, and crow, while the percentage of 

 carbohydrate is higher in short-distance fliers such as the sparrow 

 (Nair, 1952). The distribution of this fat has been shown by George 

 and Jyoti (1955), who observed that in birds such as the pigeon, 

 Columba livia, the pectoralis superficialis contained two types of fibers, 

 a narrow type in which the sarcoplasm was interspersed with fat 

 globules as well as opaque granules appearing to be liproprotein, and 

 another broader, clearer type in which these inclusions were fewer. 

 When the pigeons became exhausted from flying, the narrow fibers 

 lost their fat globules. In the kite (Milvus migrans) the pectoralis 

 superficialis contained fewer narrow fibers and less fat. The leg 

 muscles of both species consisted only of the broad fibers with less fat. 

 The leg of the fowl, however, contained a high percentage of fat. 

 Continuous excitation of pectorals or leg muscles reduced their content 

 of free lipid (George and Jyoti, 1957). These authors concluded that 

 the muscle lipid supported prolonged activity. 



The muscles supply the power for flight, while the wing and other 

 areas are the foils with which the muscles operate. These surfaces 

 are difficult to measure accurately because their artificial expansion 

 may not duplicate exactly their natural expansion. Our values rep- 

 resent an approximation of the maximal expansion and, to that degree, 

 the possible area available, but this does not tell us how these areas 

 are used or how the areas are distributed in actual performance. In 

 action there is frequent change in areas as well as in shape. Aspect 

 ratio tells us a little but fails to give the shape, camber, or potential 

 slots of the wing. The shape, stiffness, and character of the tail are 

 also needed to complete the picture. These are all factors in flight and 

 maneuverability. The combined action of the flight muscles and 

 feather "blades" and "planes" determine the performance. 



This combined mechanism is used either in flapless flight in which 

 gravity is the factor, as in gliding, or in flapping flight in which 

 muscular contraction overcomes the pull of gravity. In gliding, the 

 bird may take advantage of winds or thermal currents, or it may dive. 



The size of glide areas is not always an indication of the amount of 

 gliding or soaring done by particular species. For example, Mycteria 

 with a glide area of 1.76 cm. 2 per gram is a good soarer, while 

 Phaethornis with a glide area of 7.14 cm. 2 per gram does not glide. 

 Compare also the glide area of Parus (9.42 cm. 2 per g.) with that 

 of Stelgidopteryx (9.55 cm. 2 per g.), two birds whose activities are 

 very different. 



