The Tennessee Warbler is a plain, fast-moving warbler that most Michiganders know only as a migrant streaming through the treetops in spring and fall. Understated in appearance — olive-green above, whitish below, with a gray head, a white eyebrow, and a needle-thin bill — the breeding male is trim and clean, while fall birds are washed yellow-green and easily confused with several other drab migrants. Its song is loud and staccato for such a small bird, an accelerating three-part series of sharp notes.
Like the Cape May Warbler, the Tennessee is closely tied to spruce budworm outbreaks in the boreal forest, where its numbers surge when the caterpillars are abundant. It breeds far to the north and passes through Michigan in good numbers on migration, foraging busily high in the canopy. The name, once again, is a migration accident — the first specimen was collected in Tennessee — and the bird neither breeds nor winters there, spending the cold months in Central America.
Feeds heavily on caterpillars, especially spruce budworm during outbreaks, along with other insects gleaned from foliage high in the canopy. On migration and its tropical wintering grounds it also takes nectar and fruit, sometimes visiting flowering trees, which is unusual among warblers.
No. It was named from a migration specimen collected there. It actually breeds in the far northern boreal forest and winters in Central America, only passing through Tennessee — and Michigan — on migration.
Like the Cape May Warbler, it specializes on spruce budworm caterpillars when they are abundant on the breeding grounds. During budworm outbreaks the birds raise large families and become common; between outbreaks their numbers fall.
In spring look for a plain olive-green warbler with a gray head, a white eyebrow, whitish underparts, and a thin pointed bill. Fall birds are yellow-green and trickier, best separated from similar migrants by the white undertail and fine bill.
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