314 BREWSTER'S WARBLER. 



uals composing the brood, or it may be connected with sex, since the female 

 of Brewster's Wai-bler, I think, always retains a tinge of yellow on the breast, 

 even in the adult. I fancy the rapid loss of the veiling yellow feather-tips is 

 occasioned by their disintegration and dropping off rather than by mere mechani- 

 cal abrasion and bleaching. 



When the female pinus was first observed, although she was a typical pinus 

 in iiluniage, both Dr. Tyler and I surmised that she was a so-called impure iiinus 

 in blood, produced in accordance with the Law of Mendel from one of the many 

 crossings of chrysoptera with IcucobronchiaUs that, to our personal knowledge, 

 have occurred in this locality during the last four years; in other words, that she 

 belonged to the same family stock as the chrysopkrae and leucobronchiales in the 

 swamp. We even calculated, with lively anticipation, the chances of .seeing a 

 Lawrence's Warbler among her offspring, — a more than even chance provided 

 both she and her Golden-winged mate belonged to the mixed stock and raised 

 a brood of four or five young. This expectation (like many a hope staked on 

 young promise for its fulfilment) was not realized; all the young birds grew up 

 to be Brewster's Warblers; yet we had the full satisfaction of denK)nstrating 

 the true nature of Brewster's Warbler and removing the question forever from 

 the realm of conjecture. That all of the offspring of this pair of Inrds were 

 Brewster's Warblers would indicate that both of the parents were of pure blood. 

 By the Mendelian Law of transmission a pure chrysoptera mated with a pure 

 pinus should produce nothing but leucobronchiales; a pure chrysoptera and an 

 im]nu-c pinus will produce, on the average, chrysoptcrae and leucobronchiales 

 in equal numbers; an impure chrysoptera and a jiure pinus, in like manner, 

 pinus and leucobronchiales in the same proportion; while an imj^ure chrysoptera 

 united with an impure pinus would give rise to chrysopterae, pinus, leucobron- 

 chiales, and laivrencei in ecjual proportions. 



It is interesting to recall to mind in this connection, that Dr. Tyler saw a 

 male Blue-winged Warbler near his house on the 6th of May of this year (Auk, 

 July, 1913, 30, p. 435); this bird sang the normal song of the Blue-winged 

 Warbler, — pretty sure evidence that he was a stranger from tlic South and not 

 a member of the native Lexington colony of mixed breed, all of whom without 

 exception sing the Golden-wing's song. It is highly j^robable that on the night 

 of the 5th-6tli of May, when there was a heavy migration of W^arblers in this 

 region, a small flight of Blue-winged Warblers invaded eastern Massachusetts 

 and that the female Blue-wing that mated with the Golden-wing in the Lexington 

 swamp came in with that flight. 



