PASSERINE BIRDS OF NEW YORK 87 



plumes or bristles, moult along with the contour feathers with 

 which they are associated. In adults there is regularity in the 

 development of the tracts all bearing a fairly definite time rela- 

 tion to each other but in young birds an outbreak of moult in 

 any of the tracts earlier or later is less unusual. 



A knowledge of the distribution of the feathers of each tract, 

 their relative numbers and arrangement is indispensable in fol- 

 lowing their successive growth, but it is not possible in the pres- 

 ent paper to go too deeply into the niceties of pterylographical 

 differences. Other writers, notably Nitzsch, have discussed 

 them and mapped out the feather tracts of various species. It 

 is well to remember that among our Passerine species contour 

 feathers grow on all the tracts, a small part of the alar and 

 caudal tracts furnishing the remiges and rectrices respectively. 

 It is well to observe that these too are contour feathers a fact 

 that some writers overlook. They are renewed in adults but 

 once in twelve months as a rule and no oftener in most young 

 birds but there are exceptions among a number of species. The 

 body feathers of a great many species are renewed twice a year 

 in both old and young. 



1. Alar or Wing Tracts (Ptervlce alares). The power of flight 

 depends upon the remiges of these tracts, and until they have 

 reached maturity after the moult regularly subsequent to the 

 breeding season, there appears to be little or no attempt at mi- 

 gration on the part of most, birds, some of the Flycatchers, 

 Swallows and, perhaps, a few others, being marked exceptions. 

 As flight then, is the first object to be attained, it is not surpris- 

 ing the moult should begin where it does near the middle 01 

 each wing with the fall of the respective innermost or proximal 

 primary. In nine-primaried species it is the ninth as usually 

 counted, omitting the one aborted, and the tenth when ten are 

 found. The upper primary coverts fall with or a little after the 

 primaries to which they belong and are almost never moulted 

 independently of the primaries. As soon as a primary falls the 

 follicle or envelope containing the new forming feather pushes 

 into view, often reaching one quarter the length of the old 

 feather and a diameter exceeding it by one half before the 



