MacGillivray's Warbler

MacGillivray's Warbler (Geothlypis tolmiei) is a small, active songbird of the New World warbler family, celebrated by birdwatchers for both its striking plumage and its stealthy nature. Primarily a resident of heavy underbrush in western North America during the summer, this active insectivore spends its time foraging close to the ground. It was named in honor of the Scottish ornithologist William MacGillivray by his friend John Kirk Townsend, who first collected the species.

Identifying a MacGillivray's Warbler requires looking closely at its prominent hood and eye markings.

• Adult Males: Feature a dark slate-gray hood that completely wraps around the head, throat, and upper breast. This hood darkens to near-black on the lores (between the eyes and bill) and on the lower breast, forming a rough, dark bib. The most critical identification mark is the pair of bold, white crescents (a broken eye-ring) directly above and below the eye.
• Females & Immatures: Exhibit a much paler, washed-out gray or olive-gray hood. Their white eye crescents are generally less prominent than the male's but are almost always present and diagnostic.
• Underparts and Upperparts: Across all ages and sexes, the back, wings, and tail are a uniform olive-green, while the belly and undertail coverts are bright yellow.

Similar Species: The highly similar Mourning Warbler (Geothlypis philadelphia) ranges further east but overlaps in parts of western Canada. Adult male Mourning Warblers lack the white eye crescents entirely, showing an unbroken gray hood. Immature birds of both species can be exceptionally difficult to separate, though MacGillivray's tends to have more distinct, bolder eye crescents and a slightly longer tail.

MacGillivray's Warblers are habitat specialists of dense, early-successional vegetation and damp understory.

• Breeding Habitat: Look for them in areas of dense shrubby growth, including clearcuts, regenerating forest burns, riparian willow and alder thickets, and brushy hillsides. They favor overgrown areas from sea level up to moist mountainous areas.
• Range & Migration: This species is a long-distance Neotropical migrant. They breed throughout western North America, from Alaska and western Canada south through the Rocky Mountains and Pacific states into California and New Mexico. In late summer and early autumn, they migrate south to winter in Mexico and Central America, utilizing similar dense brush, scrublands, and forest edges.

MacGillivray's Warblers are notoriously skulking, keeping low to the ground and bouncing through thick brush. They rarely venture into open spaces, making patience essential for birders.

• Diet & Foraging: They forage actively in low, dense vegetation, gleaning caterpillars, beetles, leafhoppers, and spiders from leaves, twigs, and the forest floor.
• Vocalizations: The song is a rapid, dry, and chattering series of notes that typically ends on a different pitch, often transcribed as chur-chur-chur-chree-chree-chree. The call is a very sharp, dry, and metallic tack or tsip, which is often the first and only clue that a bird is hiding in the thicket.
• Nesting: The pair builds a bulky cup nest constructed of dry grasses, bark strips, and weed stems, lined with fine rootlets and animal hair. The nest is typically hidden very close to the ground (under 1 meter height) in dense weeds, ferns, or low shrubs.