110 PROCEEDINGS OF THE ACADEMY OF [1896, 



It is generally considered, and in many cases actually proven, 

 that the most perfect and brilliantly plumaged individuals of a 

 species are the oldest, or at least are birds of several years of age, 

 and I have followed this idea in treating of the species in the latter 

 part of the present paper. It is, however, quite likely that certain 

 individuals, whether from excessive vitality or some other cause, 

 assume the adult dress at an earlier period in their life than others 

 and that certain other individuals never attain the highest develop- 

 ment of plumage coloration exhibited by the species. 



The scarcity of adult birds in winter plumage (i. e. the dress 

 assumed at the end of the breeding season) has already been men- 

 tioned. The fact that the number of these birds taken in September 

 and October is often so remarkably small as compared with the 

 birds of the year, seems to me good evidence that they not only start 

 on their southward migration sooner than the young, but that they 

 make a more continuous journey with fewer and shorter stops. 



The diti'erence in the numbers of these birds taken by autumn col- 

 lectors is real and not imaginary. Mr. C. W, Beckham in 1887 called 

 especial attention to it\ giving the above explanation. He stated 

 that between Sept. 1 and Nov. 22, 1886, he collected 367 birds of 

 which 348 were birds of the year, the determination of age being 

 based upon examination of the skeleton. In the fall series that I have 

 examined, where the difference between the bird of the year and 

 adult was clearly indicated by the plumage, I find the proportion 

 of old birds very small ; but I think that careful collecting carried 

 on through August will result in the discovery of a large number 

 of adult birds present at that time, which leave before the usual fall 

 collecting begins. 



As a result of the studies given in detail farther on, the following 

 generalizations may be made : 

 1. The annual molt at the close of the breeding season is a physio- 

 logical necessity and is common to all birds. 

 II. The spring molt and striking changes of plumage effected by 

 abrasion are not physiological necessities and their extent is de- 

 pendent upon the height of development of coloration in 

 the adult plumage, and does not necessarily bear any relation 

 to the systematic relationships of the species. 



It naturally follows that closely related species may differ 

 materially in the number and extent of their molts, and that 



1 Auk, 1887, p. 79. 



