The Yellow-rumped Warbler, once considered 2 species, the Myrtle Warbler in the East and Audubon’s Warbler in the West, is one of the most common warblers in North America. It is also one of the most ecologically generalized: confined largely to coniferous breeding habitat, individuals forage in a broad range of microhabitats and employ a variety of foraging techniques, from fly-catching to foliage-gleaning for insects. It has a broad breeding range from Alaska south to Guatemala and east to the northeastern US. It is often abundant in winter in the southern US, Mexico, Central America and the western Caribbean.
Adult Male (spring/summer)
Head is charcoal gray with bright yellow crown and throat. Eyes have white eye crescents. Breast black; belly sides have black sides and streaks and white center; flanks yellow with thick black streaks and undertail coverts white. Nape gray; back gray with black streaks; conspicuous bright yellow rump. Scapulars gray with black streaks; wings black with white feather edging and two white wing bars. Conspicuous white tail spots with large black boarder are distinctive.
Adult Female (spring/summer)
Similar to adult male but duller overall, lacks bright yellow crown; grey-brown on forehead and nape and has more streaking on belly.
Juvenile
Similar to adult female but dull brown overall and yellowish throat.
Juvenile
Similar to adult female but dull brown overall and yellowish throat.
General:
Large, long-tailed warbler with stout dark bill. Length: 12-14cm. Wing: 19-23cm. Weight: 12-13grams.
Behaviour:
Yellow-rumped Warblers forage on outer tree canopies. They typically catch a variety of insects while in flight and males are known to forage higher than females. Their typical diet includes caterpillars, beetles, weevils, ants, and aphids. During migration and in the winter, this species will eat fruit, berries, and seeds and will occasionally feed from feeders.
Habitat:
In the summer, this warbler species inhabits open coniferous forests and forest edges. Occasionally they will be observed in deciduous forests. In the fall and winter, Yellow-rumped Warblers are located in open woods or shrubby streamside habitats, coastal vegetation, parks, and residential areas.
Information:
Yellow-rumped Warblers build cup nests for breeding, which are composed of twigs, pine needles, grasses, moss, lichens and moose, horse, or deer hair. The nest is lined with hair and feathers. The nest is places on a horizontal branch of a conifer. A typical clutch has 1-6 eggs that are white with brown speckling. Incubation lasts 12 to 13 days and nestlings fledge after 10 to 14 days.
Similar species:
Yellow-throated Warbler, Magnolia Warbler, Black-and-white Warbler.
Conservation Status:
The Yellow-rumped Warbler is listed as Least Concern and are common widespread.
A relatively short distance migrant, the Yellow-rumped Warbler migrates through Colony Farm in large numbers. Capture rate is highest during Spring Migration as seen by the peak in April and May and slightly lower during Fall Migration.
Molt Summary:
PF: HY partial (Jun-Sep); PB: AHY complete (Jul-Sep); PA partial (Dec-May)
Preformative molt usually includes all med & gr covs and often the greater alula, but no terts or rects.
Adult PA includes 0-10 inner gr covs, but no terts or rects
Ageing and sexing wood warblers in the spring requires a complete understanding of the molt cycle of the individual species being studied. All of these birds will have undertaken a prebasic molt following the breeding season last year when adults replace all body and flight feathers. In species where the annual prebasic molt is the only molt occurring annually breeding occurs in basic plumage and the result when looking at an adult bird, which has undertaken this complete definitive prebasic molt, in the spring is that there are no discernible molt limits on the wing between replaced and retained feathers.
However, in many species there is a SECOND molt that occurs prior to the next prebasic molt called the prealternate molt which occurs in the late winter/early spring. This molt occurs in both adults and first year birds so that in the spring first year birds will show three generations of feathers but adults will also show molt limits but only two generations of feathers between adult prebasic and adult prealternate feathers.
Many Setophaga warblers have extensive prealternate molts in the late winter/early spring which results in adult birds having molt limits but unlike second year (SY) birds which show 3 generations of feathers, juvenal, formative and first alternate, adult birds show only two, adult basic and adult alternate.
The differences between Audubon’s (below left) and Myrtle (below right) groups of Yellow-rumped Warbler is illustrated in this photo, Audubon’s with the plain face and yellow throat compared to Myrtle with the distinct supercilium and black auricular and white throat.
Juveniles have underparts with heavy streaking. Juv M=F, although sexing some birds may be possible by the amount of white in the rects, as in HY/SYs below, and (occasionally) juvs of AUWA with yellow in the throat can be sexed male.
The preformative molt is partial and usually includes all median and greater coverts and often the greater alula. This HY female in September however has replaced all median coverts, the carpal covert and greater alula covert A1 (red arrows) but has retained all of the greater coverts and main lower alula feathers.
Notice also the narrow, tapered outer primary coverts with no pale buffy-brown edging contrasting with the replaced carpal covert.
Sexing Yellow-rumped Warblers in the fall is a complicated assessment of multiple plumage characteristics and wing length.
Males tend to have broader and darker black side streaking than females and the yellow spot under the wings also tends to be much brighter and cleaner in males. In addition to side streaking, upper tail coverts are useful in sexing some birds, males having feathers with broad, dark black centers that are neatly and cleanly edged in gray and female upper tail coverts have a narrower dark center band and are broadly edged in gray with buffy/brown. However, many Yellow-rumped Warblers in the fall cannot be confidently sexed and are simply recorded as ‘sex unknown’.
This SY male in April is showing 3 generations of feathers. In its preformative molt following the breeding season last year it replaced lesser, median and greater coverts, carpal covert and greater alula covert (red arrows). In its 1st prealternate molt in the late winter early spring it replaced inner median and greater coverts (blue arrows); primaries, secondaries, primary coverts and lower two main alula feathers are all retained juvenal feathers.
Notice the narrow, tapered and abraded outer primary coverts and main alula feathers with little pale edging and compare with the spring adults below.
This SY male in May is showing the same 3 generations of feathers, the preformative molt limit between the outer greater coverts and inner primary covert and 1st prealternate molt limit between the 1st prealternate inner greater covert (GC 5) and formative outer greater covert (GC 4). Notice the mix of formative and 1st prealternate lesser and median coverts and that the greater alula covert (A1) is a retained juvenal feather in this bird.
Notice again the lightly pigmented and washed out appearance of the retained juvenal primary coverts and alula with no bluish-gray edging.
This SY in April has abnormally replaced the two innermost primary coverts in its preformative molt last fall. The close up provides a good opportunity to compare the difference in shape, quality, wear, sheen, gloss, rachis colour and edging between replaced adult and retained juvenal primary coverts.
And the above photo is shown side by side with an adult (ASY) male below. Again compare the difference in shape, quality, wear, sheen, gloss, rachis colour and edging between replaced adult and retained juvenal primary coverts and alula.
This AHY female in August is showing no discernible molt limits, the lesser coverts with brownish edging, greater coverts with broad whitish fringes and primary coverts more truncate and with relatively distinct grayish edging. Notice also the blackish main alula feathers with no contrast between them and the greater alula covert (A1).
A similar example of an AHY female in September with no discernible molt limits, the lesser coverts again with brownish edging, greater coverts with broad whitish fringes and primary coverts more truncate and with relatively distinct grayish edging. Notice again the blackish main alula feathers with no contrast between them and the greater alula covert (A1) and compare both of these adult female photos with the HY female in September at the top of the page.
This ASY male Myrtle Warbler in May is showing a prealternate molt limit (blue arrow) between the outer four greater coverts replaced as part of the birds definitive adult prebasic molt last year and the six inner greater coverts replaced as part of its adult prealternate molt this spring. Notice the difference in wear to the tips between the adult prebasic and adult prealternate greater coverts.
Notice also the broad, truncate primary coverts with distinct bluish gray edging and lack of contrast between the alula feathers.
This ASY male Myrtle Warbler in April is showing a prealternate molt limit (blue arrow) between the outer four greater coverts replaced as part of the birds definitive adult prebasic molt last year and the six inner greater coverts replaced as part of its adult prealternate molt this spring. Thus there are only two generations of feathers, adult prebasic and adult prealternate.
Notice also the broad, truncate primary coverts with distinct bluish gray edging and lack of contrast between the alula feathers.
This ASY male also in April is showing a similar prealternate molt limit in the greater coverts (blue arrow) having replaced all body and flight feathers in its definitive adult prebasic molt after the breeding season last year and the inner greater coverts again in its adult prealternate molt in the late winter early spring.
Notice also the broad, truncate primary coverts with distinct bluish gray edging and lack of contrast between the alula feathers.
This ASY male also in April is again showing a pattern of replaced inner greater coverts and has also replaced the innermost tertials (S8 & S9) as part of its prealternate molt.
Notice again the broad, truncate primary coverts with distinct bluish gray edging and lack of contrast between the main lower alula feathers and greater alula covert (A1).
Although tail shape is not reliable for ageing Setophaga warblers as all age classes can show rounded retrices the extent of white on retrices r2 to r6 of this adult (ASY) male and the extensive black centers to the uppertail coverts (red arrow) are both reliable indicators to confirm age determination when combined with molt criteria above.
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