Colima Warbler

The Colima Warbler is a subtly plumaged wood-warbler best known not for bright colors but for its extremely limited US range. It breeds almost exclusively in wooded canyons of the Chisos Mountains of Big Bend National Park, Texas, drawing birders from across the country for that single reason, though it is fairly common in the mountains of Mexico further south.

Overall the bird is a soft grayish-olive above and pale buffy-yellow below, with a chestnut crown patch that is usually concealed and only flashes into view when the bird is excited or preening. A crisp white eyering and bright yellow-orange undertail coverts add the only real accents to an otherwise understated plumage.

Key field marks

• Gray head and back with a faint olive wash
• Chestnut crown patch, often hidden
• Bold white eyering on a plain gray face
• Bright yellow undertail coverts contrasting with a paler grayish-buff breast
• Long tail for a warbler, often pumped or flicked

Similar species

• Virginia's Warbler: smaller, grayer overall, with a distinct yellow patch on the breast that Colima lacks (Colima's underparts are more uniformly pale buff).
• Lucy's Warbler: much smaller, paler, with a chestnut rump rather than crown, and lacks the yellow undertail coverts' brightness of Colima.
• Nashville Warbler (in migration elsewhere): brighter yellow underparts overall and a smaller range overlap.

Habitat

Colima Warblers favor open oak and oak-pine woodland on steep, shaded mountain slopes and canyons, typically between about 1,650 and 2,300 m (5,400-7,500 ft) elevation, where madrone, pinyon, and juniper often grow alongside oaks.

Range

In the United States the species breeds only in the Chisos Mountains of Big Bend National Park, Texas, making it one of the most range-restricted breeding birds in the country. Its core range lies in the Sierra Madre Occidental of Mexico, extending south through Chihuahua, Durango, and neighboring states.

Migration

Colima Warblers are short-distance migrants, withdrawing from the Chisos Mountains in fall to winter in west-central Mexico, then returning to breed by April.

Behavior

Colima Warblers forage actively but deliberately through the mid-story and canopy of oak woodlands, gleaning insects and spiders from leaves and bark, often working along horizontal branches with a slow, methodical pace compared to some more hyperactive warblers.

Voice

The song is a simple, sweet trill that accelerates and often drops slightly in pitch at the end, reminiscent of a Chipping Sparrow's trill but richer and more musical. The call is a sharp, dry chip.

Nesting

Nests are built on the ground or in low vegetation on steep, brushy slopes, tucked among grasses, leaf litter, or the base of shrubs where they are extremely well concealed. Females typically lay 3-4 eggs, and both discovery of nests and detailed breeding biology data remain relatively limited due to the bird's remote habitat.