32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



Flapping flight may be in the form of "sculling" as in the gull, 

 hovering as in the hummingbird, or rocketing as in the pheasant 

 (Jack, 1953). 



Although we have employed the ratio, wing area per gram of body 



weight, for comparisons, the wing loading ( — r- — ] could be 



used, as was done by Jack (1953). Perhaps buoyancy index is to be 

 preferred. 



It is interesting that when a sex difference is shown in wing areas, 

 as in the case of sex differences in heart and flight muscles, it is the 

 male that shows the larger values, except in Cassidix mexicanus, in 

 which the reverse is true. 



In some manakins, as well as in the motmot, larger wing areas 

 occur in specimens collected at high altitudes than in those collected 

 at sea level. Traylor (1950) reported that some species from a high 

 altitude possessed longer wings than those from lower elevations. 



We have reported 39 of the species discussed by Poole (1938), 

 many of whose values are from single specimens. Seven of his species 

 possessed a smaller wing area per gram of body weight than ours. 

 In the following comparisons, his values are given first and ours 

 second : Dendroica pensylvanica, 5.45-7.0 cm. 2 per gram ; Centurus 

 carolinus, 3.00-3.79 ; Cyanocitta cristata, 2.65-3.39 ; Falco sparverius, 

 2.74-3.50; Sturnella magna, 1.83-2. 16; Buteo lineatus, 2.1 1-2.90; and 

 Cathartes aura, 1. 81-2.98. In all these species his specimens had larger 

 body values than ours. In addition, three species with about the same 

 body values had smaller wing values. They are Dendroica virens, 

 6.35-7.30; Mniotilta varia, 6.13-6.85; and Stelgidopteryx ruficollis, 

 6.79-7.54. Finally, his specimens of three species with smaller body 

 values than ours possessed larger wing areas. They are : Fulica 

 americana, 1. 37-1. 00; Strix varia, 3.59-2.49; and Ardea herodias, 

 2.33-2.06. These differences might be due to individual variation or 

 to seasonal changes. 



The tail is so variable in size, shape, and character that it may or 

 may not be generally a factor in aerial locomotion. In many instances 

 it has been observed to be useful in maneuvering. However, if the 

 tail is small, the wings take over its function, as in the swift or duck. 

 In the latter, on the other hand, because of the small wings together 

 with the speed, the course of flight cannot be changed quickly. 



The speed at which a bird flies is determined by the shape, size, and 

 rate of beat of the wing and the angle of attack. Of course, the speed 

 at which a bird can fly when pressed is not necessarily the speed that 



