PASSERINE BIRDS OF NEW YORK 75 



which has been determined by dissection, and the age, when pos- 

 sible, by osteological characters. I have obtained several thous- 

 and of such birds and studied them before they were skinned, 

 and also prepared hundreds of young birds in early stages of 

 plumage. Among large series of the commoner species, I have 

 birds taken every month in the year and oftener, so that not 

 only are all the successive plumages illustrated, but in many 

 species all the intermediate transition stages. Gaps in some of 

 my series that a lifetime of field work might not fill have been 

 bridged to a certain extent through the kind assistance of 

 friends. The extensive collections in the American Museum of 

 Natural Histoiy have been put at my disposal by Doctor J. A. 

 Allen and Mr. F. M. Chapman. Mr. William Brewster has 

 accorded me like privileges with his private collection and Mr. 

 Robert Ridgway has furnished me with birds from the collection 

 of the United States National Museum, while Mr. Charles F. 

 Batchelder, Mr. Witmer Stone and Mr.WiLLiAM Palmer have 

 all furnished me with specimens to throw light on obscure points. 



Equipped with such material, it has been possible for me to 

 tread safely where others have slipped, and possessing in it a 

 key which fits locks hitherto unopened, I have endeavored to 

 use it to the best advantage. There may be little that is 

 quite new in these pages, for many have traversed the subject 

 before me, but no one has taken just my point of view, and my 

 work has been on absolutely independent lines. Nothing what- 

 ever has been taken at second hand, and every statement is for- 

 tified by specimens to prove its truth. No previous attempt 

 has been made to link together the successive plumages of so 

 many species, and yet this very linking together of isolated facts 

 affords the only highroad by which we may arrive at a true un- 

 derstanding of plumage or of moult. Specimens are isolated facts, 

 and hundreds of them taken at the wrong season may prove 

 nothing, while one taken at the proper time may prove everything, 

 provided the principles of moult are understood. Quality and 

 not quantity of material for study determines its value. 



Moult and plumage truly go hand in hand ; moult a vital 

 process at definite inter\-als for the production of new feathers. 



