14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



Pipridae. — Among the manakins, Corapipo and Schiffornis have a 

 high heart value of 1.50 percent, compared to 1.06 percent for 

 Manacus and 1.11 percent for Pipra. In view of the practice of 

 dancing on the part of the male, larger leg muscles than in the female 

 might be expected. In Corapipo we found no great difference, but in 

 Manacus the leg muscles of the male were larger than those of the 

 female (11.91 percent compared to 8.42 percent). Moreover, the leg 

 muscles of Manacus were larger than those of other manakins. Lowe 

 (1942) mentions that the pectoralis and thigh muscles of the male 

 are very well developed. 



Cotingidae. — The cotingas, birds of the forest, are peculiar to the 

 warmer parts of the Americas. Arboreal in habit, they possess strong 

 flight equipment for movement among the tree tops (22 to 33 percent 

 flight muscles; buoyancy index, 3.28 to 4.83; aspect ratio, 1.65 to 

 2.00). The hearts are large (i.ii to 1.45 percent) and the legs 

 moderately so (5.15 to 8.18 percent). 



Tyrannidae. — The tyrant flycatchers constitute one of the largest 

 families of American birds (365 species, according to Van Tyne and 

 Berger). Those found south to Panama are mostly arboreal, darting 

 from a strategic perch to capture insects. There is great variation in 

 their musculature, heart size ranging from 0.71 to 1.88 percent and 

 flight muscles from 16 to 33 percent. Large and broad wings (buoy- 

 ancy index, 3.39 to 4.71 ; aspect ratio, 1.46 to 2.05) give great maneu- 

 verability. The muscles of the lower extremities show considerable 

 range (3 to 7.35 percent). Their adaptations for catching prey or for 

 bold attacks in defense of territory are quite varied. The genus 

 Todirostrum in proportion to its size has much larger muscles of the 

 lower extremities and smaller flight muscles than do other members 

 of the family. 



Hirundinidae. — As swallows spend much time in the air, their 

 legs are very small, being used only for perching (lower extremity 

 muscles, 1.80 to 2.84 percent), yet their flight muscles are not unusu- 

 ally large (19.7 to 25 percent). All except Progne have very large, 

 narrow wings (buoyancy index, 4+ ; aspect ratio, 2.3 to 2.6) and 

 fairly large tails. 



Corvidae. — The jay family contains the largest passerine birds and 

 some of the most aggressive ones. Although fairly strong fliers (flight 

 muscles, 20 to 25 percent; buoyancy index, 3.4 to 4.7), they use their 

 feet extensively in walking and manipulating food (lower extremity 

 muscles, 10 to 15 percent). Their hearts are of moderate size (0.85 

 to 1.0 percent). 



