BREWSTER’S WARBLER. 315 
The history of the other pair in the swamp, a male Brewster’s Warbler and 
a female Golden-wing, may be told in a few words. As in one of the two cases 
of a male Golden-wing joined with a female Brewster’s Warbler, considered in 
detail in my memoir published in 1911, a majority of their issue were Brewster’s 
Warblers, but one of them a male Golden-wing. Dr. Tyler banded two of the 
little birds belonging to this brood on the 19th of June, when they were but a day 
or two out of the nest and as like each other as two peas from one pod; one of 
these grew up to be a typical Brewster’s Warbler while the other, its own brother, 
became a typical male Golden-wing. If any of the birds that were banded 
(three in all) return and breed in their native place next summer, we may be 
able to establish a family pedigree for these interesting hybrids, extending 
through three generations, complete as regards both the male and the female 
lines. 
In my paper published in 1911, after stating the different hypotheses pro- 
posed in order to explain the relations existing among the Golden-winged, Blue- 
winged, Brewster’s, and Lawrence’s Warblers I added, half in jest, that the only 
hypothesis left for a new-comer in the field was this: that the Golden-winged 
and the Blue-winged Warblers themselves were merely two forms of one species. 
Curiously enough, not long after this I found that this very opinion had been 
expressed, and in a most unexpected quarter: in a letter dated Edinburgh, 
Sept. 15, 1835, Audubon wrote to Bachman that he suspected the Golden- 
winged Warbler and the Blue-winged Warbler were one species!’ That Audubon 
at that early date, ignorant (as he was assumed to be) of the existence of 
Brewster’s and Lawrence’s Warblers, and but superficially acquainted with the 
Golden-wing, should suspect that two birds so diverse as the Blue-wing and 
the Golden-wing were one species seemed incomprehensible, and in the light of 
what we now know about these birds, his surmise seemed to presuppose an 
almost superhuman faculty of prevision. 
As a possible explanation of Audubon’s letter I have only this to offer: 
in the winter of 1876-77 Dr. Spencer Trotter ° discovered in the collection of the 
Academy of Natural Sciences of Philadelphia a specimen of Brewster’s Warbler 
without a label, the third specimen known up to that time; on the bottom of 
1This letter is among the many unpublished MS. letters of Audubon in the Wade collection, 
generously presented to this Museum by Mr. John E. Thayer. 
2See Proc. Acad. Nat. Sci. Phila. for 1877, Jan. 1, 1878, p. 292; Bull. Nuttall Ornithol. Club, 
Jan., 1878, 3, p. 44, Jan., 1879, 4, p. 59. 
