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Winter: Southern middle America and the northwestern tip of South America, primarily in Panama, northern Colombia, and northwestern Venezuela. Breeding habitat Inhabits dense, boreal forests, especially stands of mature spruce-fir, pine, hemlock, or mixed forest, that is broken by small clearings, swamps or bogs. Does not usually nest in deciduous forest, but will in response to caterpillar outbreaks. Occasionally uses Norway spruce plantations. Conservation status The Bay-breasted Warbler is of moderate conservation concern because of its relatively narrow breeding range (primarily in belt of closed boreal forest in Canada), and its even narrower winter range in tropical lowland forests. Because of its use of mature forest stands with tall conifers for breeding, studying the effects of fragmentation and largescale silvicultural practices is important for the Bay-breasted Warbler's conservation. Populations have declined significantly in a large portion of this species' range, particularly in Maine and the Maritime provinces. Description Male: Distinctive breeding plumage consists of rich bay colors on the crown, throat, sides, and flanks, coupled with a distinct black mask covering the face and forehead. Two white wing bars are prominent, as is a buffy patch on the neck; white corners can be seen on the tail. Female: A drab greenish and buffy warbler with two prominent white wing bars; diagnostic markings include buff or rufous wash on the flanks and breast, a bay-colored crown-patch, a split, buffy eye-ring, and mottled blackish cheeks. Juvenile: Dull olive-gray and strongly streaked above; buffy-white and spotted with dusky marks below. Also shows a yellowish tinge on the sides of the head. Vocalizations Song: The Bay-breasted Warbler's song is composed of 5-10 very high, thin, squeaking single or double notes, varying little in pitch, rendered as se-atzee-atzee, or seetzy-seetzy, seetzy, seetzy-see. The number and pattern of single and double notes varies among individuals. The song is generally soft and very high pitched, one of the highest of any of the North American wood-warblers. The tonal quality and pattern is similar to Cape May Warbler, from which Bay-breasted Warbler is nearly indistinguishable by human ears. Calls: A high-pitched, loud, and buzzy call note, zip or zee, is given both in flight and while feeding. A sharp-sounding metallic chip and a tititi call are both given in alarm. Also gives a loud, sweet chip. Foraging strategy Generally gleans prey from the mid-level, inner part of coniferous trees, particularly on lichen-covered limbs with little foliage, but readily forages at other heights within the tree and in broad-leaved foliage. Movement is primarily in a radial direction around tree, or moving along branches, or short flights to adjacent branches. Occasionally sallies or hovers to capture insects. Diet Primary food items are caterpillars, beetles, flies, moths, and budworms. Specific prey include click, ladybird, leaf-eating, June and other beetles, house flies, gall flies, Mayflies ants, lace-winged flies, ichneumon flies, moths and their cocoons, and canker worms. Outbreaks of spruce-budworm, which affect fir as well as spruce trees, and black-headed budworm have been shown to affect territorial behavior and clutch size (see “Behavior and Displays” and “ Nesting-Eggs” below). Behavior and displays
Courtship
Nesting Nest site: Often located on the limb of a dense conifer 4.5-10 feet (1.5-3.0 meters) out from the trunk. Favored tree species are black spruce or balsam fir, but occasionally nests in a pine or hardwood in a mixed-forest habitat, or, less frequently, in shrubs. Sometimes nests on the edge of coniferous forest where it joins secondary deciduous forest. Height: Usually 12-25 feet (4-7 meters) above the ground in the lower third of a tree, but can range from3-40 feet (1-12 meters) and may be placed as high as top of tree. Nest: Cup-shaped with a thick rim and a relatively thin bottom. Sides are fragile and constructed of loosely woven conifer twigs, bark shreds, coarse dried grasses, lichen, insect and spider silk, spider webs, and plant down; the cup is lined with fine rootlets, pine needles, hair, moss, and fine grasses. Nest built by female, who is accompanied by male. Eggs:4-7, usually 5, occasionally 6. Clutch size varies with spruce-budworm outbreaks in boreal coniferous forests. The white, creamy white, pale bluish-white, or pale greenish-white eggs are boldly speckled, spotted, or blotched with brown or chestnut colors. Shell is smooth and glossy. Incubation period: Incubation by female alone, 12-13 days. Nestling period: Nestlings are altricial and covered with brown down at hatching. For the first few days the female broods the young while male brings food to the female. Female often trembles, slightly droops and rapidly flutters her wings when the male arrives at nest; the male responds by passing food to female. Although both parents bring food to young, the female feeds nearly 3 times as much as the male. Young leave the nest at 10-11 days. Fledgling period: Young are able to stand and fly short distances upon fledgling, but remain close to the nest and are fed by adults for several days after departure. In one instance, both adults and 1 young were still in the nest 8 days after the rest left the nest. Broods: No information. Cowbird Parasitism: Rare host for Brown-headed Cowbird, as the ranges of these two species rarely overlap. Notes
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in Canada and the U.S. Ninety percent of range lies in Canadian boreal forest,
extending west to British Columbia but with the bulk of the breeding population east of
Ontario. The remaining 10% breeds in the northern U.S., primarily in Maine. Elsewhere in
the U.S., it is considered an uncommon to rare breeder. Breeding range does not extend
south along Appalachian Mountains, as is the case for several other northern breeding
warblers. 
