Identification

Large (total length 13–15 cm, mass ~15 g), ground-dwelling New World warbler. The body is ovoid, the wings are long, and the bill and legs are large and strong. Connecticut Warbler is unusual among most warblers in that, for the most part, it walks instead of hops.

Predominantly olive to olive-brown above and yellow below with a complete and conspicuous whitish to white eye ring in all plumages. Adult males (in Definitive Basic and Definitive Alternate plumages) have gray to blue-gray heads and breasts, the breast with variable dark gray to slate mottling or up to a solid patch, and bright yellow lower underparts. Adult females are similar but duller, especially on the head and nape, which can be dull grayish to grayish brown and lacking black on the lower breast.

Juvenile Plumage, retained for only a week or so following fledging, is mottled brownish or olive with a buff eye ring. First-year birds (in Formative Plumage and First Alternate Plumage) resemble adult females but can be even duller, with dull olive to brownish-olive crowns, buff throats, and duller yellow underparts. First-year males average brighter and grayer heads than first-year females, especially in First Alternate Plumage during spring. First-year birds can also be separated from adults by molt limits among wing feathers and more worn, narrower, or more pointed retained juvenile primaries and rectrices (see Plumages). All age/sex groups become slightly brighter in spring (alternate plumages) than in fall and overwintering period through a combination of molt and feather wear.

Unlikely to be confused with other species except for the (formerly congeneric) Mourning Warbler (Geothlypis philadelphia) and MacGillivray's Warbler (Geothlypis tolmiei). The Connecticut Warbler is distinguished from these by its larger size, stockier build, and its complete whitish or white eye rings (not broken or lacking). The breast of the male is gray without or sometimes with dark gray to slate mottling, lacking the distinctly black feathering of the adult and spring male Mourning Warbler and MacGillivray's Warbler. All males in MacGillivray's Warbler and some males in Mourning Warbler also have dark lores (1 Pitocchelli, J. (1990). Plumage, morphometric and song variation in Mourning (Oporornis philadelphia) and MacGillivray's (O. tolmiei) Warblers. Auk 107:161–171. Close ), which are absent in Connecticut Warbler. The Connecticut Warbler has complete eye rings in all ages and sex classes. MacGillivray's Warbler has broken eye rings, or “eye arcs,” but never a complete eye ring (2 Pyle, P., and P. Henderson (1990). On separating female and immature Oporornis warblers in fall. Birding 22:223–229. Close ). Most adults in Mourning Warbler lack white around the eye, but some can show white eye arcs or spots (1 Pitocchelli, J. (1990). Plumage, morphometric and song variation in Mourning (Oporornis philadelphia) and MacGillivray's (O. tolmiei) Warblers. Auk 107:161–171. Close ), and the eye ring is much thinner and less bold than in Connecticut Warbler (JP).

Adult female and first-year Connecticut Warbler have brownish-olive hoods and distinct eye rings (2 Pyle, P., and P. Henderson (1990). On separating female and immature Oporornis warblers in fall. Birding 22:223–229. Close , 3 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ), in contrast to first-year Mourning Warbler and MacGillivray's Warbler, which have gray hoods and eye arcs. Occasionally, female or first-fall Mourning Warbler can have rather complete eye rings, but these are always thinner and often are broken (incomplete) in front or behind the eye, in contrast to the complete and full eye ring of Connecticut Warbler (2 Pyle, P., and P. Henderson (1990). On separating female and immature Oporornis warblers in fall. Birding 22:223–229. Close ). In their first-fall (Formative Plumage), Mourning Warbler has a more yellowish throat and first-fall MacGillivray's Warbler has a grayish throat; both differ from the buff throat typical of first-fall Connecticut Warbler. Underparts of Connecticut Warbler, especially in its first-fall, are duller yellow compared to Mourning Warbler and MacGillivray's Warbler.

Lanyon and Bull (4 Lanyon, W. E., and J. Bull (1967). Identification of Connecticut, Mourning, and MacGillivray's Warblers. Bird-Banding 38:187–194. Close ; see also 3 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ) used external wing and tail measurements to distinguish adult Mourning Warbler, MacGillivray's Warbler, and Connecticut Warbler. The difference of flattened wing minus tail ranges from 19–27 mm (n = 148) in Connecticut Warbler, the largest difference among the three species. There is no overlap in this value with either Mourning Warbler, which ranges from 10–16 mm (n = 109), or MacGillivray's Warbler which ranges from 2–11 mm (n = 150). See Measurements for more details.

Connecticut Warbler only superficially resembles the much smaller Nashville Warbler (Leiothlypis ruficapilla), which can also have olive upperparts, gray head, and a white eye ring, but its underparts are yellow from tail to throat (minus white in the lower belly near the vent), so it lacks the hooded appearance of the Connecticut Warbler. Further, the bill of Nashville Warbler is small and sharp, unlike the large and longer bill of Connecticut Warbler, and the legs are much smaller and not pinkish as in Connecticut Warbler. Likewise Connecticut Warbler can be superficially similar in plumage to females of the Common Yellowthroat (Geothlypis trichas), but the former is larger with a blunter bill, and has greener upperparts, yellow concentrated on the lower underparts rather than the throat, and a more complete and whiter eye ring.

In addition to plumage and leg color, Connecticut Warbler differs from all of these other wood-warblers in being larger and more rotund, tending to be more terrestrial (inhabiting lower branches and the ground under vegetation), moving more sluggishly, and walking rather than hopping.