26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



and glide areas nearly twice those of Manacus collected at sea level, 

 but this may not be an altitude effect. 



Ratio of buoyancy index. — Values for the buoyancy index are 

 shown in table I. Cathartes tops the list with 5.86. Nyctibius and 

 Casmerodius tie for second place, and Pandion is third, Tyto fourth, 

 Coragyps fifth, and Cochlearius sixth. The lowest is Manacus (2.79). 



ASPECT RATIO 



The ratio of the length to the width of the wing, or aspect ratio, 

 indicates the adaptation for soaring or quick takeoff — the long, narrow 

 wing (high ratio) for soaring, and short, broad wing (low ratio) for 

 prompt takeoff. Most small birds possess a low ratio, the cuckoo being 

 the lowest. Exceptions are goatsuckers, trogons, potoo, shore birds, 

 swallows, and hummingbirds, which are high, the last three being the 

 highest. Of the heavier birds. Chaemepetes is the lowest, while the 

 gull, frigate-bird, and pelican are the highest of all birds studied. The 

 barn owl has a longer wing than the other owls that we have studied. 

 Corvus has a much larger aspect ratio than the other corvids observed. 



TAIL AREAS 



The relative size of the tails is shown in figure 7. The tails in grebes 

 were so small that they were not measured. They are small in shrikes, 

 rails, jacanas, and tinamous, and large in Fregata, Anhinga, falconids, 

 cracids, cuculids, some strigids, the nyctibiids, caprimulgids, trogons, 

 dendrocolaptids, furnariids, tyrannids, corvids, parids, mimids, tur- 

 dids, sylviids, Ptilogonys, and f ringillids. Hummingbird tails are rela- 

 tively the largest of all. The tail of the turkey vulture is larger than 

 that of the black vulture. 



The size of a tail does not necessarily indicate its effectiveness, since 

 it may be an ornament as in the male quetzal. However, in most 

 instances it can be a factor in steering, gliding, or soaring. 



GLIDE AREAS 



The combined areas of wings, tail, and body make what we have 

 called the glide area. An examination of table 1 will show that these 

 areas tend to parallel the wing areas (see fig. 6). This is to be ex- 

 pected, since the wings constitute a large proportion of the total, the 

 tail being relatively small in most instances. In those birds in which 

 glide areas are much larger than the wing areas, the large tails usually 

 account for the increase, as in trogons and cuckoos. In a few birds 



