Orange-crowned Warbler

The Orange-crowned Warbler is found in shrubs and low vegetation. It is common and widespread in the west, but much less common in most of the east. It breeds widely over much of western and northern North America and east across Canada. It winters in the southern US, Mexico and northern Central America.

Adult Male (spring/summer)

Dusky olive-green head with pale olive-yellow supercilium, small black eye-line and broken eye-ring. Crown has faint orange line. Bill is black and sharp. Back, rump, uppertail coverts and wing coverts dusky olive-green. Flight feathers are dark with olive-green edges. Breast, belly, and flanks are drab yellow with blurry olive streaks. Undertail coverts are yellow.

Adult Female (spring/summer)

Plumage is duller than male and orange crown maybe absent.

Juvenile

Plumage is duller and may show buffy wing bars.

General:

Small, sharp-billed drab warbler. Length: 11-14cm. Wing: 19cm. Weight: 7-11grams.

Behaviour:

The Orange-crowned Warbler moves quickly from perch to perch as it probes or gleans insects from leaves, moss, branches, and grasses. Prey that are resting in the foliage or flying might sometimes be hawked. They feed on insects, berries and occasionally nectar.

Habitat:

Prefers habitats with shrubs and low vegetation, often in patchy oak or aspen forest, or in riparian areas or chaparral. Ideal breeding habitat is low shrubby areas with moderately dense foliage along steep slopes and close to water. During migration it frequents habitats riparian willows and scrub oak chaparral.

Information:

Orange-crowned warbler is divided into four subspecies. Leiothlypis celata celata is the dullest of the four and it occurs in Alaska and across Canada. L c lutescens occurs along the Pacific coast and is the brightest yellow. Intergrading between these two subspecies in appearance is L c orestera from the Rocky Mountains and Great Basin. L c sordida is dark green but is found only from southern California to northern Baja California and the Channel Islands. During the breeding season the male will sing from the tops of tall trees. Breeding females construct an open cup nest of twigs, bark and grass and that is lined with finer materials on or close to the ground. 4-6 reddish-brown speckled white eggs are laid. The species is monogamous and both parents feed the young. A group of warblers may be called a “bouquet”, “confusion”, “fall” or “wrench”.

Similar species:

Nashville Warbler, Philadelphia Vireo, Tennessee Warbler, Yellow Warbler.

Conservation Status:

Listed as Least Concern. Abundant but may be experiencing gradual, long-term decline.

Capture Rates:

A breeding bird in Colony Farm, capture rates of the Orange-crowned Warbler are relatively consistent from early spring through August. Numbers do peak however in September due to juvenile dispersal as well as a higher frequency of migrants moving to their wintering grounds in the southern U.S. and Central America.

Molt Summary:

PF: HY partial; PB: AHY complete; PA absent-limited
Preformative molt includes all med and gr covs, sometimes 1 – 3 terts (rarely s6) and occasionally 1 – 2 central rects (r1; to all rects in lutescens and sordida)
PA is limited primarily to the head and chin, is more extensive in SY M than in other age/sex groups.

The 4 subspecies of Orange-crowned Warbler (OCWA) vary markedly in colour, the pacific coastal (lutescens) subspecies (below left) with brighter yellowish-olive head, upperparts and underparts and the Interior (orestera) subspecies (below right) with duller grayish-olive plumage. 

These grayish-olive birds (particularly the celata subspecies) can be confusing particularly in the fall looking more like Tennessee Warblers (TEWA) but OCWA has yellowish undertail coverts (versus whitish in TEWA) and always has a yellowish ‘face’ and blurry grey breast streaking which is always lacking in TEWA.

In many species of warblers, sparrows and vireos the preformative molt is partial with all lesser, median & greater coverts replaced but no tertials or other flight feathers. In OCWA this partial preformative molt can include a number of tertials and occasionally central retrices.

This HY in August has completed its partial preformative molt and replaced all lesser, median, great coverts and carpal covert, the molt limit indicated between the outer greater covert and inner primary covert (red arrow). Notice also the thin, tapered outer primary coverts and lower main alula feathers with only very feint greenish-olive edging contrasting with the replaced greater coverts.

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 like this bird. Molt limits can be quite subtle 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.

The tail of the same HY bird in August is showing very tapered and sharply pointed outer rectrices with very feint greenish-olive edging.

Tail shape is generally more tapered in hatch year birds and more truncate in adults although determining the age of birds by tail feather shape alone is generally not very reliable because of individual variation and the possibility of accidental loss and replacement (i.e. adventitious molt). Tail shape should always therefore be used with caution and only in conjunction with other ageing criteria (e.g. molt limits).

This HY also in August has again replaced all lesser, median, great coverts and carpal covert, the molt limit indicated between the outer greater covert and inner primary covert (red arrow). Notice also the contrast between the replaced greater alula covert (A1) and retained juvenal lower main alula feathers (red arrow).

Again notice the thin, tapered outer primary coverts and lower main alula feathers with little or no greenish-olive edging contrasting with the distinct and broad olive-green edged replaced greater coverts.

The tail of the same HY bird in August showing tapered outer rectrices with little greenish-olive edging.

The tail of this SY in May shows how retained juvenal tail feathers begin to show extensive wear by spring. Notice the abraded, tapered and brownish outer rectrices with virtually no olive-green edging.

Feather exposure to sun and abrasion is the major cause of feather deterioration and is especially hard on juvenal feathers. Exposure wears down feathers both through structural weakening and break-down as a result of solar irradiation, and through physical abrasion against foliage and the ground. Because juvenal feathers are of poor quality, they tend to wear down and fade more rapidly than subsequently grown feathers.

This HY bird in fall is again showing very fresh retained juvenal feathers, the molt limit is between the replaced outer greater covert and retained inner primary covert (red arrow). Primary coverts are retained feathers in all examples of partial preformative molts.

Notice again the contrast between the replaced greater alula covert (A1) and retained juvenal lower main alula feathers (red arrow).

Although the outer primary coverts do have some greenish-olive edging as these are still fresh juvenal feathers, the lower main alula feathers are very thin and tapered with no edging contrasting with the replaced greater alula covert (A1) mentioned above.

The two photos immediately below show molt limits in the making and illustrate the sequence of events that results in the molt limits shown in HY/SY birds above.

This typical sequence of molt of wing coverts in the preformative molt typically begins with the proximal lesser coverts and proceeds distally and toward the greater coverts as follows:

– inner lesser & median coverts
– when about half of lesser coverts
– median coverts commence
– when about half of median coverts molted
– greater coverts commence (replacement of greater coverts usually proceeds proximally)
– when about half greater coverts replaced
– tertials commence
– alula covert is replaced when median coverts completed
– carpal covert and alula replaced when greater covs completed
In many species, central retrices can be replaced if and when tertials are replaced.

Both of these HY birds in July are undergoing their preformative molt replacing lesser, median and greater coverts and the carpal covert (feathers in sheath) where upon they will stop molting.

In many species of warblers, sparrows and vireos, all lesser, median & greater coverts but no tertials, retrices or other flight feathers are replaced resulting in a molt limit between the replaced outer greater covert and retained inner juvenal primary covert.

Notice again the very fresh juvenal alula, primary coverts and remiges all of which are retained feathers.

Contrast the above HY wings with the wing of this AHY in September showing no discernible molt limits among the coverts or alula. Notice also the broad green edging on the lower main alula feathers not contrasting with the adjacent greater alula covert (A1).

The following 3 photos all show AHY birds in September and are prime examples of what definitive adult plumage, with no discernable molt limits among the coverts or alula, looks like in fall. There was even a trace of a feather sheath remaining on the outermost primary of the last bird, showing that this bird was near the very end of its complete definitive prebasic molt.

Again, tail shape is generally more tapered in hatch year birds and more truncate in adults, the rectrices below of the AHY immediately above are all replaced adult feathers, broader, more truncate with an obvious corner to the inner web and simply better quality feathers with more structure when compared to the first year (HY/SY) birds above.