NO. I LOCOMOTOR MECHANISMS OF BIRDS — HARTMAN 29 



rather than an altitude effect. Stieve also compared hearts of Lyrurus 

 lyrurus tetrix from different altitudes. Birds from higher levels 

 (1,800 to 2,000 m.) possessed definitely smaller hearts than those 

 living at 50 meters. The same could be shown in other species. Several 

 authors (e.g., Parrot, 1893, and Rensch, 1948) have concluded that 

 birds flying great distances or living in northern latitudes or high 

 altitudes possess larger hearts than those less active or living in warmer 

 climates. 



A thorough study of the muscles used in locomotion should include 

 the weight of each individual muscle because of the variation from 

 species to species. Since this is impossible in an extensive survey, only 

 the larger muscle groups have been weighed. The pectoralis super- 

 ficialis is the most important in flight, as it depresses the wing, while 

 the supracoracoideus is the principal levator of the wing. The re- 

 mainder of the flight muscles (called "rest" in our study) also play an 

 important role in the flight, whether it be in maneuvering or "setting" 

 the wing for the action of the "power" muscles. 



The flight muscles constitute a considerable proportion of many 

 birds, varying from 14 to 40 percent. The percentage is lowest in 

 those birds that use them least, but on the other hand, large size does 

 not always indicate extensive use. The tinamou has very large flight 

 muscles but makes only short flights. The flight muscles of the 

 hummingbird, which spends much time in the air, are also relatively 

 large, but not to be compared with those of the tinamou. The muscles 

 of Colinus, Chaemepetes, and some trogons are relatively just as large 

 as those of the hummingbird but are used much less. 



The pectoralis superficialis, much the largest of the flight muscles, 

 has received the most attention, but some authors have exaggerated 

 its size. Stillson (1954) says, "In good fliers the pectoral muscles 

 account for a large part of the total bird." Although Shufeldt (1890) 

 said that in all the birds possessed of the power of flight, the pectoral 

 muscles are second to none in importance, this is not true for grebes 

 and some of the rails. In the former the leg muscles range from 

 15 to 18 percent, whereas the whole flight musculature is 14 percent 

 or less. In Aramides the leg muscles are 24 percent, while the flight 

 muscles are less than 17 percent. 



Calculated from Fisher's (1946) data, the combined volume of all 

 muscles that may aid in depressing the wing constitute 62.7 percent 

 of the wing musculature in Cathartes and 56.2 percent in Coragyps. 



Of these the pectoralis superficialis is 60.5 percent of the total in 

 Cathartes and 54.1 percent in Coragyps. The volume of all muscles 



