/4 DWIGHT 



I. INDOOR STUDY OF MOULT 



Fundamental Principles 



The moulting of birds is a subject so complicated, so exten- 

 sive, and so difficult of study, that it is not surprising to find it 

 wrapped, e\'en to-day, in dense clouds of ignorance which ob- 

 scure the true principles underlying it. Doubts have arisen even 

 in the minds of those who have come nearest to the truth, be- 

 cause they have been unable to explain certain seasonal discrep- 

 ancies in the plumage of birds, and theories have sprung up and 

 flourished. Theories not founded on facts, must necessaril}- fall 

 to pieces when the truth is known, and the present paper sets 

 forth a number of indisputable facts derived from personal inves- 

 tigations, which, rightly interpreted, will explain not only the 

 problems of moult and plumage, but also the theories of those 

 whose published opinions differ widely from my own. It is my 

 present purpose to demonstrate the principles dominating the 

 plumages and moults of no less than one hundred and fifty 

 North American species of the great order Passercs or Perch- 

 ing Birds, and at the same time indicate the wider application of 

 these principles, which the study of other groups leads me to 

 believe prevail among all species of birds modified only by cir- 

 cumstances. 



The fundamental facts of moult have been grasped so imper- 

 fectly by some observers, that much theorizing about color 

 changes has taken the place of actual information upon the sea- 

 sonal variations of birds' plumages, and much superficial work 

 has been done, although some excuse for it may be found in 

 the existing lack of suitable specimens for stud}'. The folly of 

 guessing at age or sex from plumage characters is exempli- 

 fied in many collections, and museum collections especially con- 

 tain many undated specimens, which are positive hindrances 

 rather than helps in settling vexed questions of moult. Worse 

 than all is the great dearth of birds actually in process of moult. 

 My own collection remedies, in a measure, all these defects, for 

 the subject of moult has interested me for many years and I 

 have devoted much time to securing moulting birds, the sex of 



