2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 144 



bumble bees whose bulky, heavy bodies make one wonder how they 

 can manage ever to become airborne. What might be called the "main 

 sequence" of insects falls on a straight line well below that for the birds. 

 One might expect this to mean a generally poorer flight performance, 

 but this does not necessarily follow, since in appraising aerial ability 

 one must also take wing-beat rate and muscle weight into account. 



For birds, excluding for the moment the hummingbirds, the scatter 

 is much less, particularly at the small end of the scale. In general the 

 soaring birds have long wings, the gallinaceous birds short wings per 

 unit of total weight. When one considers the aerodynamics of soaring 

 this result might well have been expected. 



Hummingbirds fall into a very special group, for here nature ap- 

 pears to have devised an unusual model, one in which weight is pro- 

 portional to the 1.5 power of the wing length. This result is so un- 

 expected that one might well question its validity. In figure 2 the 

 hummingbird region is expanded, and I have plotted separately the 

 two sets of available data. Their self-consistency leaves little room for 

 doubt of the basic relationship. Hummingbirds cover only a small part 

 of the roster of flying animals, and it should be noted that extrapolation 

 of the hummingbird line either to larger or smaller body weights 

 would lead to aerodynamic monstrosities. I can offer no rationale for 

 the anomaly. Hummingbirds are excellent fliers, and it may be that 

 their peculiar dimensional relationships contribute to this end. 



One also sees that the hummingbirds are placed almost exactly in 

 the center of the figure ; hence they may represent a zone of transition 

 between insects and other birds. 



BODY WEIGHT AND WING AREA 



Figure 3 shows the relationship between body weight and wing area. 

 The results do not differ significantly from those in figures 1 and 2. 

 Note again the much greater scatter for insects, the increasing scatter 

 for birds as size increases, and the anomalous proportions for the 

 hummingbirds. In figure 1, however, wing length for birds is in gen- 

 eral greater per unit weight than for insects. Wing area, however, for 

 the long-winged insects is considerably greater per unit weight than 

 for the long-winged birds. 



Figure 4 is an expansion of figure 3 for birds (excepting humming- 

 birds) with a differentiation in charting for selected bird families. We 

 see that in general the birds of prey have the highest, ducks and gal- 

 linaceous birds the lowest, relative wing area. Aerial performance does 

 not necessarily track relative wing area. Ducks, for example, are strong 

 and competent fliers, making up for their small wing area by an un- 

 usually high wing-beat rate. 



