Birds. 6755 



some reason for this. As the bird hung, the distance between the feet 

 was greater than the space between the femur joints, as of course it 

 almost necessarily must be. Thus the drag on each leg is slightly 

 oblique in opposite directions, and the hallux therefore is opposed to 

 the direction of pressure, or very nearly so. These birds can there- 

 fore cling with perfect security to any vertical surface rough enough 

 to give hold to their powerful claws, and without any continuous 

 effort. You will observe from this that your correspondent was in 

 error when he stated that the tarsus could not be bent beyond 28° 

 with the tibia. It is obvious, if this were the case, that the bird's leg 

 could never be altered from the position of perching, i. e., the femur 

 directed forwards, the tibia backwards, and the tarsus forwards again. 

 This does support the bird when the direction of gravitation is per- 

 pendicular to the axis of the body or approaching it, but with a 

 clinging bird this direction of course coincides with it. If the bird 

 attempted to cling with the leg in this position, the claws, which give 

 the point of suspension, would be very little in advance of the poste- 

 rior margin of the sternum. Thus the head, the greater part of the 

 sternum, the viscera it encloses, and the powerful muscles which 

 cover it, by far the heaviest portion of the bird, would be above the 

 point of suspension. Its protuberant breast would prevent its throwing 

 this weight on the claws ; and we can hardly imagine that, thus cir- 

 cumstanced, even the powerful tail would prevent its fall backwards. 

 But by placing the feet forwards the whole body is beloio the points 

 of suspension ; the head only, or a portion of it (for the neck is drawn in 

 when the repose is complete), is above the claws. This inclination 

 to climb, as a means of escape and safety, was so strong that it over- 

 came every other. On replacing the bird on the floor it hurried to 

 me and ran up my clothes, taking refuge in the skirts of my coat. I 

 showed one of my skins to an old hog-hunter, who assured me he had 

 often seen them fly out of caves where, during their long expeditions, 

 these men stop for shelter or rest. I took care he should not confound 

 it with Hirundo pceciloma, of which I do not think there was much 

 danger. 



"I remarked in my last letter that these birds, from their occa- 

 sional appearance, and their uncertain stay in any one spot, do not, 

 like our other Hirundines, seem to hunt over a circumscribed locality, 

 but explore large districts. The little valley which cleaves through 

 the limestone down to the red conglomerate, in which this house 

 stands, consists of about a hundred acres of pasturage. It possesses 

 some unusual advantages for the observation of Hirundines; for 



