Part 5

As the demand for these Bulletins is much greater than the supply, the names of those who have not contributed to the work during recent years will be dropped from the author's mailing list.

Dr. Winsor M. Tyler has again read and indexed for this volume a large part of the current literature on North American birds and has contributed four complete life histories. Dr. Alfred O. Gross has written stories on the yellow-throats (Geothlypis trichas) and has contributed three other complete life histories. Edward von S. Dingle, Alexander Sprunt, Jr., and Dr. Josselyn Van Tyne have contributed two complete life histories each.

INTRODUCTION

William George F. Harris has increased his valuable contribution to the work by producing the entire paragraphs on eggs, including descriptions of the eggs in their exact colors, assembling and averaging the measurements, and collecting and arranging the egg dates, as they appear under Distribution; the preparation of this last item alone required the handling of over 5,600 records.

Clarence F. Smith has furnished references to food habits of all the species of wood warblers. Aretas A. Saunders has contributed full and accurate descriptions of the songs and call notes of all the species with which he is familiar, based on his extensive musical records. Dr. Alexander F. Skutch has sent us full accounts of all the North American wood warblers that migrate through or spend the winter in Central America, with dates of arrival and departure. James Lee Peters has furnished descriptions of molts and plumages of several species and has copied several original descriptions of subspecies from publications that were not available to the author.

Eggs were measured for this volume by American Museum of Natural History (C. K. Nichols), California Academy of Sciences (R. T. Orr), Colorado Museum of Natural History (F. G. Brandenburg), C. E. Doe, W. E. Griffee, W. C. Hanna, E. N. Harrison, H. L. Heaton, A. D. Henderson, Museum of Comparative Zoology (W. G. F. Harris), and Museum of Vertebrate Zoology (M. Jollie).

The manuscript for this Bulletin was written in 1945; only important information could be added. If the reader fails to find in these pages anything that he knows about the birds, he can only blame himself for failing to send the information to--

THE AUTHOR.

LIFE HISTORIES OF NORTH AMERICAN WOOD WARBLERS

Order PASSERIFORMES: Family PARULIDAE

By ARTHUR CLEVELAND BENT

Taunton, Mass.

GENERAL REMARKS ON THE FAMILY PARULIDAE

CONTRIBUTED BY WINSOR MARRETT TYLER

The family of wood warblers, Parulidae, is the second largest family of North American birds, surpassed only in number of species by the family Fringillidae. The wood warblers occur only in the Western Hemisphere; they are distinct from the Old World warblers, Sylviidae, although the two families play a similar rôle in nature's economy.

The wood warblers are largely nocturnal migrants, whose long journeys in the dark of night over sea and lake and along the coast expose them to many perils, one being the lighthouses they strike with frequently fatal results. Their notes are seldom heard from the night sky during their spring migration, but on many a calm, quiet night in August and September, as they fly overhead, their sharp, sibilant, staccato notes punctuate the rhythmic beat of the tree-crickets singing in the shrubbery and stand out clearly among the soft, whistled calls of the migrating thrushes.

The length of migration varies greatly; the pine warbler withdraws in winter only a short distance from the southern limit of its breeding range, whereas the most northerly breeding black-polls migrate from Alaska to the Tropics. In spring many species migrate at nearly the same time, apparently advancing northward in intermittent waves of great numbers during favorable nights. Flocks made up of sometimes a dozen species together flash about in their bright plumage during the week or two at the height of the migration and furnish days of great excitement to ornithologists. Their return in late summer and autumn is more leisurely and regular; in loose flocks they drift slowly by for several weeks, their southward passage evident even in daytime. The flocking begins early, soon after nesting is over, and to the north is apparent early in July, if closely watched for, even before the leaves begin to wither. The mixed fall flocks, with adults in winter plumage and young birds in duller colors, present many fascinating problems in identification as the birds move quietly along.

The literature contains descriptions of several warblers not recognized as established species by the A. O. U. Check-List (1931). Some, described and illustrated by older writers such as Wilson and Audubon, cannot be identified; others are presumably hybrids; and one, Sylvia autumnalis Wilson, the autumn warbler, is clearly the black-poll in fall plumage. The first category includes Dendroica carbonata (Audubon), the carbonated warbler, of which the Check-List says "the published plates may have been based to some extent on memory"; D. montana (Wilson), the blue mountain warbler, which is "known only from the plates of Audubon and Wilson"; and Wilsonia (?) microcephala (Ridgway), the small-headed flycatcher, of which it says: "Known only from the works of Wilson and Audubon whose specimens came from New Jersey and Kentucky respectively. There is some question whether they represent the same species."

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.

Now as Audubon was intimately associated with Bell, is it not possible that he had examined this example of Brewster's warbler? In that case, seeing that this bird's characters were in part those of the blue-wing, in part those of the golden-wing, he may have inferred the interbreeding of these two birds, and so (rather unwarrantably, it is true) their identity. If this be not the explanation of the passage in Audubon's letter to Bachman I have no other to suggest.

When Audubon came to publish his account of the Golden-winged Warbler in 1839 (Ornithological Biography, 1839, 5, p. 154) he said not a word about its connection with the Blue-winged Warbler.