PASSERINE BIRDS OF NEW YORK 137 



Some young birds undoubtedly replace the body plumage 

 extensively before they move south, as shown by specimens in 

 my collection ; others, as proved by their Juvenal dress conspicu- 

 ous for brownish wing bands, reach Guatemala or adjacent coun- 

 tries before moulting. It seems more than probable that the 

 incoming feathers observed on birds when they leave us de- 

 note a slow process of moult involving later the wings themselves, 

 an order of moult that would be a reversal of the usual method. 

 If, however, this prove to be the case then the transition would be 

 effected by a very late postjuvenal moult in young birds and the 

 first nuptial plumage would be the first winter modified by wear. 

 Some adults, like the young birds, begin to assume a few new 

 feathers before moving southwards, others reach their winter 

 haunts in worn breeding dress. That a complete postnuptial 

 moult takes place we may hardly doubt, for this moult is com- 

 mon to all species and it probably takes place during the last 

 months of the year, or just prior at least to the postjuvenal 

 moult of young birds. This would explain why all specimens 

 arriving from the south in spring are in almost equally fresh 

 plumage, whether young or old, seemingly too fresh to have 

 been worn since the previous autumn. 



I have indicated the difficulties to be overcome in studying 

 this family and the same ones confront us among the Hirnndinidce 

 and a few other species. If my conclusions are erroneous they 

 fail in matters of time rather than facts of moult. 



Milvulus tyrannus (Linn.). FORK-TAILED FLYCATCHER 



1. NATAL DOWN. No specimen seen. 



2. JUVKXAL PLUMAGE acquired by a complete postnatal moult. 



Above, including wings and tail, olive-brown ; coverts and wing-quills narrowly 

 edged with pale russet. Below, white. Orbital region dull clove-brown. Bill 

 and feet brownish-black in dried specimen. The tips of the primaries are 

 rounded and there is no yellow crown-patch. The tail is but five inches in 

 length. 



3. FIRST WINTER PLUMAGE acquired by a complete postjuv- 

 enal moult as shown by two specimens from Costa Rica, Septem- 

 ber 18 (Amer. Mus. Nat. Hist. No. 48225 $ and No. 48228 9), 



