Vol. XXIII 



1906 



Clark, Pterylosis of Swifts and Hummingbirds. 87 



Pterylosis of the Head and Neck. — In all birds, the distribution 

 of the feathers on the head seems to be more liable to variation 

 than on any other part of the body; among the Caprimulgi, for 

 example, we find that the different genera exhibit quite a notable 

 diversity in the pterylosis of the head. When we consider there- 

 fore how the whole head of the hummingbird has been altered 

 for its peculiar feeding habits, and how the plumage of the head 

 has been modified in connection with the development of the 

 gorgeous metallic colors, we should expect a characteristic ptery- 

 losis. When on the other hand, we consider how nearly in the 

 opposite direction the modification of the swift's head has been, 

 and that there is no development of a peculiar head plumage, 

 it is not strange that there are some differences in the arrangement 

 of the feathers of the head and neck between hummingbirds and 

 swifts. That these differences are due to the modification of the 

 trochiline head in connection with feeding habits is certainly sug- 

 gested, if not demonstrated, by the pterylosis of the nestling hum- 

 mingbird. A comparison of figure 4, plate III, with figure 3, plate 

 II, certainly suggests a real resemblance between the two. The 

 long, narrow frontal aptcrium shown by all adult hummingbirds, 

 is almost wanting in the nestling, as it is in swifts, while the sparse 

 feathering of the occipital region is quite as evident in Chatura 

 as in MeUisuga. On the other hand, the nestling shows clearly 

 the supraocular and nuchal apteria, and the absence of lateral 

 cervical apteria which are such characteristic features of both 

 swifts and hummers. It is a natural conclusion therefore, that 

 the fundamental plan of the pterylosis of head and neck was origin- 

 ally similar, if not identical, in the Cypseli and Trochili. 



Pterylosis of the Wings. — The general arrangement of the 

 remiges and coverts of the wing is quite similar in the two groups 

 under consideration, and such differences as occur are closely 

 associated with the size of the bird. Thus we know that, as a 

 rule, the smaller the bird, the fewer will be the secondaries, lesser 

 coverts and alula feathers, and this is well shown by the swifts 

 and hummingbirds. As regards the quincubital or aquincubital 

 condition of the wing there is no constant difference between the 

 two groups, for, as already shown, individual hummingbirds show 

 variability on this point, and neither condition is characteristie 



