Vermivora chrysoptera

Typical warbler size, shape, and bright coloration. Male has a slate-gray back and nape and a white chest and abdomen. The crown and forehead are bright yellow and contrast with a black cheek and throat patch. Thin white lines separate the crown from the cheek patch, and the cheek patch from the throat patch. The slate-gray wings have a yellow patch. In females the cheek and throat patch are gray and the back and chest may have a hint of yellow or olive.

Hybridization with the blue-winged warbler (VERMIVORA PINUS) produces two color patterns once thought to be separate species: the Brewster's and Lawrence's warblers. The Brewster's warbler has a white throat and, like the golden-winged warbler, usually has a white breast and gray back, but has a thin eye line and separate wing bars typical of the blue-winged warbler. The Lawrence's warbler has the black eye and black throat patch of a golden-winged warbler but has the yellow undersides and yellow-olive back of a blue-winged warbler. Intermediate forms occur and may result from matings between two hybrids and between hybrids and parental phenotypes. Intermediates show all degrees of variation in color hue and pattern between the parental types. Short (1963) and Gill (1980) derived a hybrid index to help distinguish among the intermediate and parental phenotypes.

NEST: coarse with an outer wrapping of bark and straw with leaf petioles protruding outward. All of about 20 nests in central New York contained many large strands of reddish viburnum bark in the bottom and outer portions of the cup (J. Confer, pers. obs.). The nest is lined with a criss-cross of fine, reddish-brown material. The cup is only two to three cm deep.

EGGS: pale cream to very pale blue with a scattering of fine reddish-brown dots concentrated at the blunt end, occasionally with a variety of other dark markings.

VOCALIZATIONS: two song types, which have been extensively studied (e.g., Ficken and Ficken 1967, Gill and Murray 1972, Highsmith 1989). One, common early in the breeding season, appears to advertise the territorial boundary and the male's presence and seems to have primarily an intersexual function. This Type 1 song is usually given intermittently during the morning for a few hours after sunrise, and sometimes shortly before dusk. The song is quite unmusical with one rasping note followed by two to eight buzzy notes on a constant, lower pitch. Phonetically this is sometimes represented as "bee-buzz-buzz-buzz." A Type 2 song is given during male to male encounters. This song is a series of staccato, rapid notes followed by a lower pitched, raspy trill. The blue-winged warbler has a song that is very similar in behavioral context and sound. Males of both species also sing the Type 2 song almost constantly for about a half hour just before sunrise from the beginning of the nesting season up to the time of fledging. Almost all males can be detected, barring inclement weather, in May and early June by their singing in this pre-dawn period. Females are usually inconspicuous and both sexes are usually secretive around the nest. However, as young fledge the adults become very noisy, frequently giving a distinctive "zzzzzp" call as they seem to lead the young from the nest or bring food to them.

BREEDING: Deciduous woodland, usually in dry uplands or areas of thick undergrowth in swampy areas; woodland edge with low cover; hillside scrub; overgrown pastures; abandoned farmland; powerline right-of-ways; recently logged sites; bogs; forest openings; territories usually have patches of herbs and shrubs, sparse tree cover, and a wooded perimeter (Confer 1992). Habitat tracts of 10-15 ha can support several pairs and are preferred over both smaller and larger areas (Confer 1992). Habitat can be created through logging, burning, and intermittent farming (Confer 1992). Habitat is ephemeral and requires periodic disturbance to return it to favorable early successional conditions. Nests on or a little above ground, in grass tuft, fern or weed clump, or concealed in herbage at base of shrub, tree, ferns, briars, or goldenrod (Harrison 1978, Confer 1992). Often the clump includes a taller stem used for descent to the nest. Nests usually at the ecotone of a forest with a field or marsh, or in a small opening in a forest (Confer 1992).

Nested abundantly in the chestnut-sprout (CASTANEA DENTATA) forests of West Virginia following the spread of the chestnut blight (Hall 1983). Commonly nest in upland sites on abandoned farmland in early stages of succession (e.g., Confer and Knapp 1981), or occasionally in logged areas (e.g., Will 1986). In the Canadian shield in Ontario, they nest "...in alder [ALNUS spp.] bogs, especially when a few taller species [of trees] are present" (Mills 1987). Several observers have mentioned nesting in powerline right-of-ways. In southern Michigan they nested in and around the edges of thickly wooded portions of tamarack (LARIX LARICINA) swamps as well as in small, brushy clearings (Will 1986). In northern Michigan, Will described their habitat as including dry fields overgrown with shrubs, and woodland clearings, as well as very wet areas that were recently logged and covered with felled trees and a homogenous cover of new saplings. Will suggested that, overall, they "...appeared to require proximal access to mature or second-growth woodlands as well as open areas in which there has been considerable invasion by brush, shrubs, and sapling trees."

Vegetative characteristics of territories have been quantified for southern, central, and northern New York (Confer and Knapp 1981, Frech and Confer 1987). In southern New York and contiguous New Jersey, nesting takes place in the Ramapo Mountains (Confer and Knapp 1981, Skully, in press). In this rugged topography, territories occurred in marshes between rock outcrops often with a perimeter of alder surrounded by forest. In central and northern New York, territories usually were located on dry, upland sites of abandoned farmland but occasionally in wet sites. All territories had areas with dense herb growth without shrubs or trees. Herb growth of at least moderate density covered 60% or more of the ground, including the growth under woody plants. All territories had patches of dense shrubs which covered about half of each territory. Tree canopy covered less than 15% of the northern and central territories but up to 40% of the southern territories. Central and northern territories usually extended no more than 20 m into a forest, while southern territories frequently extended considerably further. In wetter sites sedges (CAREX spp.) were the dominant herb and alders were the dominant shrub. In upland sites a wide variety of herbs occurred while VIBURNUM spp., narrow-leaved meadowsweet (SPIREA ALBA), and dogwood (CORNUS spp.) were the dominant shrubs.

All New York territories had a similar vegetative pattern with patches of herbs and shrubs, a few trees scattered throughout, and a tree row or forest edge forming most of the perimeter (Confer and Knapp 1981, Frech and Confer 1987). In New York, abandoned farmland undergoing secondary succession has this distinctive pattern of vegetation for only about 10-20 years. Thus, golden-winged warblers at upland sites are restricted to a specific and brief stage of succession. Because of this restriction, Confer and Knapp (1981) suggested that this warbler was in some sense a habitat specialist. However, a species that can nest in chestnut-sprout forests in Virginia, tamarack bogs in Michigan, and alder swamps in Ontario clearly tolerates a wide range of conditions. It would be valuable to determine if nesting warblers require a specific plant profile but tolerate a wide range of plant species, or tolerate a wide range of both plant profile and plant species.

NON-BREEDING: In migration and winter in various open woodland habitats, pine-oak, and scrub, often in foothill regions (AOU 1983). Found in evergreen and semi-deciduous forest, particularly the canopy, gaps, or edges and in tall second growth (Stiles and Skutch 1989, DeGraaf and Rappole 1995, Howell and Webb 1995).

Territories are about one to two ha (Ficken and Ficken 1968, Murray and Gill 1976, Confer and Knapp 1977, Confer 1992).

Produces one brood per year. Commonly renests after nest loss. Nests commonly in loose colonies of 2-6 pairs (Confer 1992). Monogamy is the norm, but polygamy occurs (J. Confer, pers. obs.). Renesting is not known to occur after a successful clutch, but can occur after an initial nest failure.

Eggs are laid in May-June. For New York, the earliest egg date is 18 May (Andrle and Carroll 1988) and the latest nestling date is 22 July (J. Confer, pers. obs.). The latter is almost certainly a renesting attempt. During three years of study in central Michigan, the first egg dates were 15, 18, and 25 May (Will 1986). Usually four to six (maximum of seven) eggs are laid per nest. Incubation by the female lasts 10-11 days. The nestling stage lasts eight to ten days (Andrle and Carroll 1988) with feeding by both sexes. Thirteen nests in central Michigan fledged an average of 3.4 young (Will 1986), while five nests in northern New York fledged an average of 2.6 young (J. Confer, pers. obs.).

HYBRIDIZATION: Hybridization between golden-winged and blue-winged warblers has received considerable attention. Three collections from zones of overlap for these two species consisted of 11%, 17%, and 22% hybrids (Short 1962, Gill 1980). Field observations, which might not detect all hybrids, indicated that hybrids comprised 3%, 10%, and 14% of three sample sites (Frech and Confer 1987). Despite some hybridization, the parental phenotypes always appear to be more common than the hybrids, which supports the contention that these are valid, but very closely-related species. Historically, the blue-winged warbler nested to the southwest of the golden-winged warbler (Gill 1980). Apparently, the abandonment of farmland and resultant areas of secondary succession provided routes for expansion of the blue-winged warbler into the golden-winged warbler range.

Hybrid phenotypes give the firsthand impression that the plumage differences between the two species are caused by two pairs of genes. The first generation hybrid (Brewster's warbler) gives the appearance of being heterozygous for both gene pairs. A much rarer form (Lawrence's warbler) gives the appearance of being homozygous recessive for both gene pairs. However, all gradations of color and all mixtures of color pattern between the two species have been noted (Short 1963, Gill 1980). This variation suggests that the inheritance of color is more complicated involving, perhaps, multiple but tightly-linked loci, incomplete dominance, or modifying genes.