NO. I LOCOMOTOR MECHANISMS OF BIRDS — HARTMAN II 



of the "rest" group. Wings of fair size give them a buoyancy index 

 of 3.2 to 3.7, and the lower extremities are of medium size (5.5 to 

 7.8 percent). The proportions of domesticated Melopsitticus are 

 similar to those of the wild forms except that the buoyancy index is 

 lower (2.84). 



Cuculidae. — Some cuckoos fly very little, and we have studied 

 only those that do more flying. In these, the power of flight varies 

 considerably. The hearts (0.50 to 0.94 percent) indicate little staying 

 power. The flight muscles are very moderate (14 to 20 percent), 

 supporting wings of a high buoyancy index (3.7 to 4.4) and a low 

 aspect ratio (1.3 to 1.8), enabling them to fly only slowly. The tails 

 are large, and the lower extremities are of considerable size (muscles, 

 7 to 15 percent) . Anis fly with a series of steady wing beats alternating 

 with short sails. The flight resembles somewhat that of the Florida 

 jay, being slow and gliding and rather labored. The hearts and flight 

 muscles are smaller in Piaya cayana (P<.oi) and Crotophaga ani 

 (P<o.oi) in specimens collected at sea level than in the same species 

 collected at 4,300 feet elevation. 



Tytonidae. — The barn owl (Tyto alba) may be grouped with the 

 typical owls with respect to muscle values, although he has a larger 

 wing than most of the others. 



Strigidae. — Owls are able to fly quietly, as their wings are soft, 

 very large (buoyancy index, 4.24 to 5.1 1), and broad (aspect ratio, 

 1.8 to 2.J) . The flight muscles are moderately powerful ( 19 to 27 per- 

 cent), and the hearts are small to medium (0.31 to 0.89 percent), the 

 largest being found in the burrowing owl (Speotyto cunicularis) . 



Nyctibiidae. — The wings of the Nyctibiidae and Caprimulgidae 

 are as large as, or larger than (buoyancy index, 4.36 to S-^)* those 

 of owls but with a very high aspect ratio (2.20 to 3.4). The smaller 

 heart (0.58 percent) of the potoo (Nyctibius griseus) is in keeping 

 with his more limited activity, since he makes but short flights in his 

 forays for insects, in contrast with the caprimulgids (0.78 to 1. 12 per- 

 cent), which sweep the air in sustained flight. 



Caprimulgidae. — The pauraque (Nyctidromus albicollis), with a 

 longer tarsus and larger leg muscles (8.28 percent) than some other 

 caprimulgids, is more active on its feet and can run swiftly. 



Trochilidae. — The hummingbird is the acrobat among birds — none 

 equals him in speedy maneuverability. He hovers and flies forward 

 or backward at will. Of his large flight muscles, the pectoralis plus 

 the supracoracoideus constitute a large proportion. Many species 

 show sex differences, and in these species the muscles of the male are 



