In the second category is Vermivora cincinnatiensis (Langdon), the Cincinnati warbler, described in 1880. “The unique type is regarded as a hybrid between Vermivora pinus (Linnaeus) and Oporornis formosa (Wilson).” Recently, in a letter dated August 3, 1948, Dr. George M. Sutton reports to Mr. Bent the discovery of a second Cincinnati warbler, taken in Michigan on May 28, 1948. He says: “Its bill and feet are large for Vermivora and its under tail coverts proportionately too long for that genus. It has only a faint suggestion of wing-barring and the merest shadow of a pattern on the outer rectrices. One of its most interesting and beautiful characters is the gray tipping of the feathers at the rear of the crown, as in O. formosus. The effect is very unusual, for the gray-tipped feathers are yellow. It is, in short, obviously a cross between Vermivora and Oporornis.”
The status of Vermivora leucobronchialis and V. lawrencii and the relationship between them puzzled ornithologists for upward of two generations. William Brewster (1876) described the former as a new species, and since that time, as Walter Faxon (1911) writes, “almost every conceivable hypothesis has been advanced by one writer or another to fix its true status in our bird-fauna.” In addition to being considered a valid species, it has been regarded as a hybrid (Brewster, 1881), as a dichromatic phase, that is, a leucochroic phase of V. pinus (Ridgway, 1887), as a mutant (Scott, 1905), and finally as a phase, “ancestral in character” (atavistic) of the goldenwing (C. W. Townsend, 1908).
Lawrence’s warbler is a very rare bird. The first specimen was described in 1874 (Herold Herrick, 1874), and since that time the bird was taken or seen infrequently, chiefly in regions where the breeding ranges of V. chrysoptera and V. pinus overlap. Consensus of opinion in the main regarded it as a hybrid between V. chrysoptera and V. pinus, as it combined characters of both the supposed parents. John Treadwell Nichols (1908) some years ago brought new light to the problem. He says:
In any discussion of the status of Lawrence’s and Brewster’s Warblers it is well to bear in mind the facts, including the much greater abundance of Brewster’s, are in accord with Mendel’s Law of Heredity, supposing both forms to be hybrids between Helminthophila pinus and H. chrysoptera. * * * All the first generation hybrids will be Brewster’s Warbler in plumage. In the next generation there will be pure Golden-winged Warblers, pure Blue-winged Warblers, pure Brewster’s Warblers, and pure Lawrence’s Warblers; also mixed birds of the first three forms, but none of the last form, which, being recessive, comes to light only when pure. The original hybrids then (which will be all Brewster’s in plumage) must be fertile with one another or with the parent species for any Lawrence’s to occur; and if they are perfectly fertile Lawrence’s must still remain a small minority. After the first generation the proportion of plumages of birds with mixed parentage should be: 9 Brewster’s, 3 chrysoptera, 3 pinus, 1 Lawrence’s.
This explanation removed the stumbling block, long believed to be insurmountable, that a black-throated bird, mating with a yellow-throated bird, could produce progeny having a white throat. Under Mendel’s Law the dominant color (white) of chrysoptera would appear by the suppression of the recessive black throat.
Fortunately, Walter Faxon (1913) not long afterward found a female blue-winged warbler mated with a goldenwing and was successful in following the resulting brood of young birds until they had acquired their first winter plumage when, fulfilling Mendel’s Law, they were all in “the garb of Helminthophila leucobronchialis,” thus establishing beyond a doubt the hybrid nature of the bird. At the end of his paper, Walter Faxon (1913) relates a bit of interesting ancient history regarding these three species of Vermivora. He says:
In my paper published in 1911, after stating the different hypotheses proposed 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 the stand was written in the autograph of John Cassin, “J. C., 20 October, 1862,” and also a badly blurred legend “Not from Bell.” An appeal to J. G. Bell elicited the response that he remembered shooting a peculiar warbler in Rockland Co., N. Y., about the year 1832—a warbler something like a golden-wing, but lacking, although in high plumage, the black throat of that species; a great many years afterward, he sold this specimen in Philadelphia but knew nothing of its ultimate fate. Dr. Trotter justly inferred that the Philadelphia Academy specimen was in all probability the very bird shot by Bell.