6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 143 



is a graceful, rather powerful flier, having somewhat larger flight 

 muscles (19 percent) and wings (buoyancy index, 3.7) but smaller 

 legs (8.6 percent). 



Fregatidae. — The man-o'-war, one of the most graceful birds in 

 the air, soars much of the time, steering by his scissors tail, but he 

 can also fly rapidly to overtake another bird. His wings are very large 

 (buoyancy index, 5.55) and extremely long (aspect ratio, 3.5 to 4.4), 

 but his pectoralis plus supracoracoideus muscles are moderate (13 to 

 17 percent). 



Ardeidae. — The large leg muscles of the herons are useful for 

 wading and stalking prey. The members of this family show a con- 

 siderable range in equipment, but the wings of all are rather long 

 (aspect ratio, 2.00 to 2.66) and large (buoyancy index, 3.68 to 5.28), 

 and all have large flight muscles (20 to 25 percent) except Ixobrychus 

 (13.89 percent). 



They vary as much in flight as in muscular equipment. Some, like 

 the great blue heron, make an awkward start on the takeoff by vigorous 

 wing strokes, but once underway the long, slow strokes carry them 

 majestically through the air. The black-crowned night heron differs 

 from other herons in having a flight more gull-like, being stronger and 

 swifter with quicker wing strokes. This is not due to the size of the 

 wing muscles, since they are no larger. The least bittern has an 

 awkward fluttering flight for a short distance, preferring to escape 

 by walking or climbing. However, on long flights he appears strong 

 and rather swift despite small flight muscles. The hearts of all herons 

 are rather small (0.57 to 0.83 percent). 



The hearts of the Florida subspecies of Butorides virescens are 

 heavier (P<o.05) than those of the same species collected in Panama. 

 This is also true for individuals of Florida caerulea and Ixobrychus 

 exilis from the two localities. The hearts (P<o.oi) and pectoral and 

 supracoracoideus muscles (P<o.o5) of Tigrisoma lineatum are larger 

 than the same features in Heterocnus mexicanus. 



Cochleariidae. — The boat-billed heron is similar to the true herons 

 in the size of its flight equipment. It is interesting to note that in an 

 immature Cochlearis, at a time when the body had almost attained 

 adult weight, the flight muscles were less than half the weight of those 

 in the adult, while the leg muscles were nearly the weight of the 

 adult's. The heart of the immature was also very much smaller than 

 that of the adult. The early development of the leg muscles was also 

 shown in a young Heterocnus mexicanus (250 g.). In this bird the 

 legs were half-grown (muscles 5.88 percent of the body) while the 



