Chestnut-sided Warbler

Setophaga pensylvanica
Order Passeriformes
Family Parulidae

♂ Adult male.— Top of head yellow; back in strong light of a greenish tinge, streaked with black; wing-bars yellowish; cheeks white; sides of throat black; a narrow stripe of chestnut-red along the sides of breast and belly. 
♀ Adult female.— Similar, but duller.
Immature.— Entire upper parts yellowish-green; wing-bars yellowish; under parts white.

Nest, in a low, slight bush, often a blackberry or a raspberry.
Eggs, white, speckled, chiefly about the larger end, with reddish-brown.

The Chestnut-sided Warbler is a common summer resident of New York and New England, but is less common in the lower Hudson Valley than farther north. It arrives early in May and stays till the end of September. fers dry roadside thickets or clearings, and though its song closely resembles that of the Yellow Warbler, the two species are so rarely found breeding in the same kind of country that one will not often confuse their songs. The singer in the dry scrubby thickets is nearly always the Chestnut-side, while the bird of the streams and cultivated land is the Yellow Warbler.

Each of these two warblers commonly has two quite distinct songs, one strong and incisive, the other feebler and less piercing. The sharp incisive song of the Chestnut-side ends with a phrase which has suggested the rendering, Very, very glad to meet you. The loose or feeble song has so little character that it is hard to learn.

The yellow crown of this bird, and the white throat, breast, and belly make it easy to recognize, even if the narrow line of chestnut is not at first seen. The yellowish wing-bars of the young, and their greenish-yellow backs, and white, unstreaked under parts, distinguish them from other young warblers.

Hoffmann – A Guide to the Birds of New England and Eastern New York (1904)

Distinguishing Characters

Adults of both sexes may be known by their chestnut sides, yellowish wing-bars, yellow or yellowish crowns, the wholly different young by bright greenish yellow upperparts, yellow wing-bars, white eye-ring, grayish cheeks and underparts.

Length (skin), 4.50; wing, 2.50; tail, 1.95; bill, .35. [inches]

♂ Adult Male, Spring.- Crown yellow, forehead white; back greenish yellow broadly streaked with black, the nape grayish; tail black margined with gray the three outer feathers with white patches at the end of the inner web; primaries margined with grayish, inner flight-feathers with yellowish, median coverts tipped, greater coverts tipped and margined with yellowish; ear-coverts and sides of neck white enclosed by a black post-ocular stripe and black patch below the eye and on the side of the throat, from the latter springs a bright chestnut stripe which, broadening, passes along the sides to the flank, rest of underparts white.

♂ Adult Male, Fall.- Above bright greenish yellow indistinctly streaked on back and rump; tail and wings as in Spring ♂, whole side of head gray, eye-ring white; the sides and flanks chestnut, rest of underparts white.

♂ Young Male, Fall.- Similar to adult o in Fall but with less, or no chestnut on sides.

♀ Adult Female, Spring.- Similar to adult ♂ in Spring but duller, black areas less pronounced, tail and wings browner, chestnut stripes less developed. 

♀ Adult Female, Fall.- Similar to young ♂ in Fall.

♀ Young Female, Fall.- Similar to adult ♀ in Fall but always without chestnut on sides.

Nestling.- Above brown indistinctly streaked with black; below pale brownish, the belly white; wings and tail as in young, the coverts tipped with buffy.

The Bird and its Haunts

The regret occasioned by the decrease in the numbers of wood-inhabiting birds following the destruction of the forests in which they lived, is in a measure tempered by a knowledge of the fact that their places will be filled by other species. The Chestnut-sided Warbler, for example, considered by Wilson and Audubon to be a rare species, is now abundant, and we may believe that this change in numbers is due largely to the development of those scrub and second growths in which the bird delights.

In my own experience, covering the past twenty-five years, at Englewood, N. J., I have seen this Warbler become established as an increasingly common summer resident, and at East Orange, in the same state, Dugmore writes “What has been most noticeable about the bird-life of this particular locality is the rapid and steady increase of the Chestnut-sided Warbler.” In the summer of 1897, he adds, he did not observe a single specimen but in 1900 they had become comparatively common.

About Cambridge, Mass., Brewster, quoting Dr. Samuel Cabot, says that this species was very rare in eastern Massachusetts prior to 1835, but that it gradually and steadily increased in numbers after that date. Brewster adds “they nest chiefly on the edges of upland woods, in neglected fields and pastures, along the courses of brooks, and on country roadsides. In general terms they may be said to occupy most of the country which the Yellow Warblers avoid, but in a few localities the two species breed together in the same thickets. Both birds, as a rule, shun evergreen trees, although the Chestnut-sided Warbler occasionally frequents white pine woods in late summer, especially when it is consorting in ‘mixed flocks’ with such pine-loving species as the Chickadee and the Black-throated Green Warbler.”

Gerald Thayer writes that the Chestnut-sided is “an abundant roadside and brush-land Warbler throughout the Monadnock region, but on the mountain itself is not common above 2,000 feet, or thereabouts. Its ‘beat’ lies between the ground and the tops of small deciduous trees. The few nests I have seen have all been between two and five feet from the ground, in bushes. The adults’ peculiar markings and droop-winged, perk-tailed, and deep-chested attitudes are too well known to bear dwelling on here. Though potentially quick moving, the Chestnut-side is by no means restless, as Warblers go,— often spending many minutes at a time in one small tree, and it is one of the tamest of the tame.” (Thayer, MS).

Herrick’s detailed studies of the nesting habits of the Chestnut-side show how little we know as yet of the more intimate, personal side of the home-life of Warblers.

Song

 “The Chestnut-side, a full-voiced Warbler, has at least two main songs, both of which, but particularly the more liquid and less articulate one, are subject to wide variation. Both types of song are too liquid to be well suggested by English syllables, except for the clearly enunciated ending of one of them, wee–chew. Twit–a–wit–a–wit–a–wit-wee–chew! is something like the phrasing of the whole of this song, except that it fails to express the soft fluency of the first part. The other song is an elaboration of this initial rolling warble, with the wee–chew left off. Hardly any two Chestnut-sides sing this inarticulate song alike, and almost every individual plays noticeable variations on his own version of it. In addition to all this, the Chestnut-side is a mocker. One we used to hear, that regularly began his wee-chew song with a loud, long, rattling trill, almost indistinguishable from the more fluent song of the Sparrow; almost indistinguishable from the more fluent song of the Sparrows; and another, that lived near Catbirds, used several unmistakable notes of Catbird song. One of the Chestnut-side’s two or three or more small call-notes is characteristic, the others scantily so, if at all.” (Thayer, MS.)

Miss Paddock writes that the first two of the songs given below are usual. They are uttered with much energy and decided accent. The last two songs are more like the Redstart’s but are without accent, and sound as if sung with closed mouth.

Nesting Site

Throughout its range this species appears to nest in low bushes, saplings or briers, at from one to six, but usually about two feet from the ground.

Nest

The nest is externally rather roughly made of coarse grasses, strippings of weed-stalks, plant fibers, bunches of spiders’ webbing, and some plant down, finely and thickly lined with brown rootlets, grasses and horse-hair.

Eggs

4 or 5, usually 4, rarely 5. Ground color white to creamy white, beautifully marked, in most cases, with chestnut, varying shades of brown, lavender, and purplish brown and blackish, either in the form of a wreath or a conglomerate mass of spots on large end there being very few scattering spots over rest of egg. Some specimens of the egg of this species closely approach many eggs of the Yellow, Magnolia, Myrtle, and Prairie Warblers. Size; average .66x.49; extremes measure .61x.47, .71x.51, .66x.46 and .69x.52.

Frank M. Chapman – The Warblers of North America (1917)