Description:

MacGillivray’s Warbler is the close western counterpart of the Mourning Warbler. It is a skulking bird that spends much time low, well within dense brush and thickets. Its major physical distinction is the prominent white eye arcs above and below each eye.
John K. Townsend first named this warbler Tolmie’s warbler after Dr. W.T.Tolmie, an ornithologist, surgeon and entrepreneur with the Hudson’s Bay Co. Later, however, J.J.Audubon renamed the species MacGillivray’s in honour of a close friendship with Dr. W.MacGillivary, a Scottish ornithologist.
This wood warbler is found over much of the west from southeastern Alaska to New Mexico and as far east as western Nebraska. The first breeding birds arrive on territory in coastal B.C. in late April to early May. Its winter range is from Central Mexico to Panama.

Identification:

General: This is a medium size warbler with prominent white eye-arcs above and below each eye witch is present in all plumages. It has a weakly bi-coloured bill and pink legs. It is 13 cm long and weighs 10.5 g.

Adult Male: Gray hood; black lores; white arcs above and below the eyes and variable dark slate mottling on lower throat. Olive upperparts and bright yellow below.

Adult female: Similar to male but hood and throat paler; chin whitish and yellow below slightly paler than male.

Juvenile: Gray of forehead, crown and nape slightly tinged with olive-brown. Chin and throat very pale gray, becoming darker gray; slightly mottled on the lower throat forming a hood border. Juveniles have either a broken or complete white eye ring.

Similar Species: The Orange Crowned Warbler with yellowish underparts, particularly birds of the race ‘orestera’ are very similar. The Mourning Warbler lacks the white eye arcs, but otherwise is very difficult to distinguish from Oporonis tolmiei.

Behavior: This warbler haunts dense thickets, where it forages by hopping along the ground or among lower twigs of shrubs and trees for insects. It is timid and elusive.

Habitat: Prefers cut-over or fire-swept areas of second-growth woodland, dead and fallen trees, brushy areas near low moist ground; brushy dry hillsides not far from water, thicketed draws and canyons as well as dense willows along stream bottoms.

Information:

During breeding season the male becomes bolder and often sings, alternating between thickets and a treetop perch throwing back its head and putting much effort into its liquid song.
This species hybridizes with its eastern equivalent, the Mourning Warbler where ranges overlap.
The nest is between upright stems of shrubbery 2-5ft above ground in dense, moist places and is loosely built of weed stalks, straws, dried grasses lined with fine materials. The nest usually contains 4 white or cream-white, brown speckled eggs.

Conservation Status:
Populations appear to be stable, and the species’ acceptance of brushy habitats, which are successional to logging, suggests that widespread declines are unlikely. Populations at the southern limit of the range in coastal central California, the mountains of southern California, and in Mexico are a small and fragmented, and could be vulnerable.