MacGillivray’s Warbler

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. Geothlypis tolmiei 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.

Adult Male (spring/summer)

Dark slate-gray head, nape and throat and upper breast; bold white eye-arcs; black lores connect across forehead; olive-green back and wings; yellow lower breast, belly and flanks. Legs are pinkish-brown.

Adult Female (spring/summer)

Similar to male but head, nape, throat gray-olive; chin whitish gray; dull yellow lower breast, belly and flanks.

Juvenile

Similar to adult female but duller overall with paler throat.

General:

This is a medium size warbler with prominent white eye-arcs above and below each eye witch is present in all plumages. Length: 10-15cm. Wing: 19cm. Weight: 9-13grams.

Behaviour:

This warbler haunts dense thickets, where it forages by hopping along the ground or among lower twigs of shrubs and trees feeding at or just above ground level 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:

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.MacGillivray, a Scottish ornithologist. 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.

Similar species:

Mourning Warbler, Connecticut Warbler, Orange-crowned Warbler.

Conservation Status:

Listed as Least Concern. 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.

Capture Rates:

Capture of MacGillivray’s Warbler occurs from spring through the summer and early fall (April – September). Capture rates however, are at their highest in spring into early summer (May and June). MacGillivray’s Warblers are medium to long distance migrants, moving south for the winter as seen by our zero capture rate between October – March.

Molt Summary:

PF: HY partial; PB: AHY complete; PA limited-partial
Preformative includes all median and greater coverts but not the greater alula, tertials or rectrices.
1st PA includes 0-3 inner gr covs but no terts or rects.
Adult PA usually includes no gr covs, terts or rects.

Ageing wood warblers in late summer/early fall requires close scrutiny as molt limits can be difficult to see when hatch year (HY) birds still have very fresh retained juvenal feathers.

This wing of this HY female in August is a good example of this. Under magnification the contrast between replaced lesser, median, greater coverts and carpal covert and retained primary coverts and main alula feathers (A2/A3) can be seen the molt limits indicated with red arrows between the outer greater covert and inner primary covert and greater alula covert (A1) and main lower alula feather (A2). Molt limits like this can be quite subtle with birds in the hand and for this reason, especially after adults of these same species begin to show signs of approaching the end of their complete prebasic molt age should always be confirmed by additional criteria such as skull ossification.

Again, the molt limit on this HY male in August is quite subtle, this bird having replaced lesser, median and only 4 inner greater coverts (red arrow). Notice the slightly fresher and more olive-green edged replaced inner and paler tipped retained outer greater coverts. Notice also the very subtle molt limit between the replaced greater alula covert (A1) and retained lower alula feathers. The indistinct narrow greenish edging on the alula and the primary coverts are due to very fresh retained juvenal feathers which will disappear due to wear by spring. Again, at this time of the year age should always be confirmed by additional criteria such as skull ossification.

This SY male in May is showing lots of wear to the coverts and looks to have replaced only lesser and median coverts in it’s preformative molt. Notice the subtle molt limit between the replaced greater alula covert (A1) and lower main alula feather (red arrow).

The wing of this ASY male in May is also showing quite a lot of wear but there are no obvious molt limits between the greater coverts and primary coverts or between the greater alula covert (A1) and lower main alula feathers, the amount of wear being consistent between and among feather groups.

The tail of this ASY male in May is showing the broader, more truncate outer rectrices with very little wear typical of adult birds. Note also the ‘corner’ on the inner web of the these feathers (red arrow).