76 BREWSTER'S WARBLER 



itely ascertained facts. The interbreeding of leucobronchialis with 

 pinus, and with chrysoptera, of pinus with chrysoptera, and of lawrencei 

 with /imMj is recorded on unquestionable evidence. Here alone, there- 

 fore, we have indisputable knowledge of sets of relations which in 

 their subsequent stages are bound to produce the most varied results, 

 accounting for every phase of plumage of the lawrencei type of which 

 we have any knowledge. 



Doubtless our most satisfactory observations in this connection 

 have been supplied by Dr. Walter Faxon who writes : "In the summer 

 of 1910, there bred within the confines of a camp of about fifteen 

 acres in Lexington, Mass., a pair of Golden-winged Warblers and two 

 male Golden-winged Warblers mated with two female Brewster's 

 Warblers. . . The progeny of the three pairs were closely observed 

 from the juvenile (in one case, from the natal) plumage up to the 

 first winter plumage, when the adult characters were acquired; the 

 young of the pair of Golden-wings were all Golden-wings ; one of the 

 Brewster's Warblers that was mated with a Golden-wing brought forth 

 a homogeneous brood of Brewster's Warblers, while the other pro- 

 duced a mixed brood of Brewster's Warblers and at least one Golden- 

 winged Warbler. A striking thing about it was this : the young birds 

 of mixed parentage were absolutely pure in plumage, — either Brew- 

 ster's Warblers or Golden-wings, without any tendency to combine as 

 'intermediates' the characters of the two parents." (Mem. Mus. Comp. 

 Zool., XL, No. 6, Aug. 1913, 311.) 



Two years later, in the same locality, Dr. Faxon (1. c.) made 

 even more definite and conclusive observations in regard to the breed- 

 ing of these birds which apparently fully justify his "satisfaction of 

 demonstrating the true nature of Brewster's Warbler, removing the 

 question forever from the realm of conjecture." 



In a word, he found a typical male Golden-winged Warbler mated 

 with a typical Blue-winged Warbler, and kept their young (number 

 not stated) under observation from June 15, about two days after they 

 had left the nest, until they "all grew up to be Brewster's Warblers." 



The same season a male Brewster's Warbler was found mated 

 to a female Golden-wing and of their young one "grew up to be a 

 typical Brewster's Warbler, while the other, its own brother, became 

 a typical Golden-wing." These two birds and one from the brood first 

 mentioned were banded, and a beginning was thus made for the study 

 of succeeding generations. 



