84 lawre^xe's warbler. 



considerably. Below are given three of the theories advanced in explanation of this 

 problem. 



Mr William Brewster, writing in 1881, ( see Bulletin of the Nuttall Ornitho- 

 logical Club, Vol- VI, p. 218 ) and in 1886, ( see Auk, VoL II, p. 411 ) thinks that 

 both forms are hybrids, the result of a union between the Blue-winged and Golden- 

 winged Warblers. His reasons for so thinking being that both of the tbrms in dis- 

 pute occur along the line where the two species from which he claims they originate 

 overlap, and, furtherm )re, that both Lawrence's and Brewster's Warblers show ev- 

 ery stage of plumage between what he considers the two parent forms. This being 

 especially true in regard to Brewster's, which, as I have related, also sometimes 

 sings like both of its supposed parents. Underdate of December 10, 1902 Mr. Brews- 

 ter writes me as follows :- " Of the complete inlergradation of Icucobroncliialis and 

 lawi-encii with each other and with finiis and clirysoptera I have seen the most con- 

 \ incing evidence, although this is not furnished by my series alone ". 



Mr. Robert Ridgeway formerly considered Brewster's Warbler as a color phase 

 of Ihe Golden-wing, and Lawrence's as a color pliase of the Blue-wing (see Auk, 

 II, 1885, p. 359 ) ; that is, he thinks that both of what we may, for convenience, call 

 the parent forms, are double colored, iust as we find the Screech Owl, the Rough- 

 legged Hawk and some other birds double colored. The cause of this double color* 

 ation being unknown, but itappears to be due to extreme individual variation. Lat- 

 er, in his Birds of North and Middle America (1902, p, 454 ) Mr. Ridgeway says j 

 "" that dichromati- m as well as hybridism enters into the question of their origin ; in 

 other words,, while H. pinns apparently exhibits, rarely, a white and gray ( instead 

 of jellow and olive-green ) phase, and H. chrysoftern, as rarely, a yellow and olive- 

 green, instead of a white and gray, phase, the two species interbreed to such an ex* 

 tent, not only with one another, but with H. Icucobronchialis and //. laivrcncii ( the 

 hybrids being fertile inter se ) that the problem is a very complicated one and there-* 

 lore most ditlicult to work out satisfactorily", 



In the re\ised edition of my Birds of Eastern North America, 1896, pages 577- 

 78. I advanced the theory that both Brewster's and Lawrence's Warblers were not 

 hyljrids between //. finus and //. cJiryf'Oficra, cr color phases of either of them, hut 

 were incipient species derived, within a comparatively short tiine, directly from the 

 (jolden-winged Warbler. Below I give my reasons for this conclusion. 



In 1889 I had an opportunity, through the kindness of Mr, Brewster, ofe-xam' 

 iiiing his large series of skins of Warblers of the genus Hchnint/iop/iila. Previous 

 to making this examination I had discovered one difference between the Blue-winged 

 Warbler and the Golden-winged that appears to have escaped the attention of all 

 who have described the birds, whicii is, tl.at in tlie Golden-wing the terminal white 

 spoi on the i.iner web of the second (not the first) tail father does not extend along 

 tlie vein quite to its termination (see Fig. 40, a), whereas in the Blue-wing, this 

 spot does extend along the vein quite to its termination (see Fig. 41 ). Upon exam- 

 ining Mr, Brewster's s-ries ( between fifty and sixty of each species) I found that in 

 a large percentage of each species this character holds good. In about five percent 

 of the Golden-wings I find that the white does extend along the shaft to its termina- 

 tion, and in one or two cases it even encroaches upon the outer web, thus crossing; 

 the vein. In a smaller percentage of Blue-wings I find that the white does not ex- 



