| The male Bay-breasted Warbler changes colors during the year. During the breeding season the male has rust colored flanks, throat, and crown. The face and forehead are black with buff patches on the cheeks. The upperparts black with streaking and buff underneath. In the fall, the male plumage becomes similar to the plumage of the immature males and females. They are olive above with two wing bars and only a trace of the chestnut color on the sides. The Bay-breast has dark legs and a habit of wagging its tail when foraging. The call is a thin buzzy series of high pitched notes sounding like "seea-seea-seea", similar to the call of the Black-and-White Warbler.
The breeding habitat consists of the open spruce and fir forests and occasionally the adjoining deciduous forests that stretches from New England across southern Canada further north in western part of Canada. During their mid-May migrations, when the males are sporting the breeding plumage they are a favorite of bird watching enthusiasts. In late August or September and sometimes later the Bay-breasted Warbler heads for its wintering grounds from Costa Rica to the northern part of South America.
When the male arrives he will defend his territory by singing, however the territories will become constricted when food is abundant as is the case during spruce budworm outbreaks.
The clutch consists of 4 to 5 white or off-white eggs marked with brown or black at the larger end. The number of eggs may increase during spruce budworm outbreaks. The eggs are incubated by the female for about 12 to 13 days and leave the nest about 11 or 12 days later. The male will feed the incubating female at the nest and both parents feed the young after hatching. The nest is usually placed 5 to 50 feet above the ground on a horizontal branch of a conifer tree and is constructed of twigs, lichens, and grass, and lined with rootlets or hair. Unlike most warblers, this bird is usually not parasitized by the Brown-headed Cowbird.
The Bay-breasted Warbler is one of the most beneficial of birds to the logging industry. Their numbers will increase dramatically during outbreaks of the spruce budworm thus helping to keep that tree destroying insect under control. They will furtively hop slowly and deliberately along branches and from branch to branch as they forage for insects, wagging their tail. This was one of the birds that Robert MacArthur studied is showing that warblers that appear to occupy the same niche in nature actually forage in different parts of trees. This warbler tends to forage in the inter part of the understory along level branches as opposed to the warblers that forage near the ground or near the tree tops. Besides the budworm, this warbler also dines on flies, caterpillars, beetles, moths, and grasshoppers. They also consume smaller amounts of berries especially in its winter territories where they gather in mixed flocks.
Length: 5 to 6 inches
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