Glenn Bartley/Vireo

MacGillivray's Warbler

Geothlypis tolmiei

Conservation status Still common in its range, although some surveys have suggested a slight decline in numbers.
Family Wood Warblers
Habitat Low dense undergrowth; shady thickets. Breeds in thickets of willow and alder, near stream bottoms or at edge of coniferous or mixed forest. Favors new growth in logged or burned areas (especially with dead and fallen trees), brushy thickets near low moist ground, and thicketed mountain canyons. In winter in the tropics, occurs in forest undergrowth in foothills and mountains.
A skulker in dense western brush, sometimes hard to see but readily located by its hurried song and its hard chip callnote. A close relative of the Mourning Warbler of the East, replacing it from the Rockies westward. Unlike the Mourning, this species is often seen in substantial numbers during migration -- especially in early fall, when practically every thicket in the Southwest seems to have one (but only one) MacGillivray's Warbler.
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Feeding Behavior

Forages mostly close to ground in dense thickets, seeking insects on branches and among foliage. Hops when searching for insects on the ground. On the wintering grounds, individuals defend feeding territories and usually forage alone.


Eggs

Usually 4, sometimes 3-5, rarely 6. Creamy white with brown spots, speckles or blotches. Incubation is by female alone, about 11-13 days. Apparently cowbirds do not commonly parasitize this warbler's nests. Young: Both parents feed the nestlings. Young leave the nest about 8-9 days after hatching.


Young

Both parents feed the nestlings. Young leave the nest about 8-9 days after hatching.

Diet

Mostly insects. Details of diet are not well known, undoubtedly feeds mostly on insects. Known to eat click beetles, dung beetles, alfalfa weevils, flea beetles, caterpillars, and other insects. Young birds in Colorado will take sap from borings in willows drilled by sapsuckers.


Nesting

Male sings frequently through breeding season to defend nesting territory. Nest site is well hidden in dense shrubs, often placed in upright fork of fir saplings, scrub oaks, alders, salal, chokecherry or Spiraea. Usually 2-3' above the ground, sometimes lower or as high as 5' up. Frequently in shady damp places or amid tall weeds and ferns. Nest is loosely constructed open cup made of weed stems, bark shreds, and dry grass; lined with fine grasses, rootlets, and hair. Both sexes probably help build nest.

Text © Kenn Kaufman, adapted from
Lives of North American Birds

Illustration © David Allen Sibley.
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Migration

Probably migrates mostly at night. Migration is spread over a lengthy period in both spring and fall.

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Migration

Probably migrates mostly at night. Migration is spread over a lengthy period in both spring and fall.

Songs and Calls
Song a chanting tree tree tree tree sweet sweet! Call a loud tik, sharper than the calls of most other western warblers.