Life Histories of North American Wood Warblers, Part One and Part Two. Arthur Cleveland Bent

       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.

      [Author’s Notes: When I asked Dr. Tyler to contribute these remarks we discussed Professor Cooke’s (1904) theory of trans-Gulf migration, which has been generally accepted until recently, when it was challenged by George C. Williams (1945). This paper started a discussion in which George H. Lowery, Jr. (1945), has taken a prominent part, and of which we have not yet heard the last. Routes of migration from South America to the United States are evidently well established through the West Indies and the Bahamas to the southeastern States; across the Caribbean to Jamaica, Cuba, and Florida; through Central America and directly across the Gulf from Yucután to the Gulf States; through eastern Mexico and Texas; and through western Mexico to the southwestern States. Professor Cooke was probably correct in assuming that the majority of wood warblers breeding in eastern North America migrate directly across the Caribbean or the Gulf. Some species may confine themselves to only one of the routes named, but we need more data to say just which species uses what route.]

      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,