NO. I LOCOMOTOR MECHANISMS OF BIRDS — HARTMAN 35 



muscles of the goatsuckers, together with rather small legs, suggest a 

 life in the air for the capture of prey. 



In the hummingbird, with tiny legs, large pectoralis, supracora- 

 coideus, and heart, and wings with a high aspect ratio, together with 

 large tail and glide area, we have the most capable and most active of 

 the airborne birds. It possesses both speed and maneuverability. It 

 hovers, flies in any direction, flies like an arrow or, on long trips over 

 water, describes an undulating course (Murphy, 1913). Trogons, 

 with somewhat broader but large wings and moderate hearts, would 

 be good fliers, while kingfishers, with smaller pectoral muscles than 

 the trogons, would be less powerful. The small heart of the motmot 

 indicates little sustained activity, which would also be true for the 

 puffbird. Barbets, with large legs and small pectoral muscles, suggest 

 more footwork. Toucans likewise possess less powerful pectoral 

 muscles and large legs. 



In the woodpecker large, broad wings and a moderately powerful 

 pectoralis enable it to flap and glide alternately. Its sizable legs sug- 

 gest active use. The woodhewer is similar, except that a somewhat 

 smaller heart could support less activity. In the ovenbird, the larger 

 heart and a smaller pectoralis, together with larger legs, go with 

 greater activity in the form of less flying and more footwork. In 

 similar fashion the antbird seems to be adapted to ground activity. 

 The cotingas and flycatchers have large, powerful wings, with medium 

 to small legs and moderate hearts. 



Large wings with a high aspect ratio and a very large heart are 

 found in the very active swallow. The various values for the crows 

 and jays suggest moderate activity. Many of the small perchers can 

 be included in the classification of the large, broad-winged kinds but 

 with varied pectoral muscles and leg power. The wrens have large 

 legs and small pectorals. The thrushes should be better fliers, using 

 their legs less. The troupials make much use of their legs, as do also 

 some finches. 



Among all these birds two groups are most striking : The timamous, 

 with large flight muscles, large lower-extremity muscles, and the 

 smallest hearts ; and the hummingbirds, with the largest hearts, large 

 flight muscles, and very small lower-extremity muscles. 



Our data show that muscle weights are just as characteristic as is 

 body weight, and this, coupled with the values of certain muscle 

 groups, helps to identify the species. Beddard ( 1898) said, "the muscu- 

 lar system of birds is remarkably constant for the species." He was 

 referring to the presence and arrangement of the individual muscles. 



