Canada Warbler Cardellina canadensis
Version: 2.0 — Published May 7, 2020
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Medium-sized, brightly colored New World warbler. Total length 14 cm (range 12–15), wing span 20–22 cm, body mass typically 9.5–12.5 g; female slightly smaller than male (2, 3, 4, 5). In adult male upperparts (rear crown, rear auriculars through tail and wings) bluish gray, underparts (chin through belly) bright yellow. Forehead and fore crown, lores, and anterior auriculars black, separating yellow and gray portions of head. Yellow supraloral stripe and complete whitish eye ring forming prominent “spectacles.” Black area extends beneath eye along side of throat joining with a series of vertical rows of black spots that run across upper breast (necklace). Undertail coverts white. No wingbars or tail spots. Female similar to male but duller overall, with paler, less distinct black markings on head and breast. Adult plumages are similar throughout year.
Immatures of both sexes are similar to adults but somewhat duller, with indistinct breast streaking and facial markings (6, 7). However, there is considerable individual variation among young and older age classes. Immature female is dullest, and may have a very pale necklace, but always shows enough of adult pattern to be recognizable. Older fledglings acquire the faint necklace early.
Typically, one of the easiest New World warblers to identify in any plumage. Its unmarked gray upperparts (note absence of wingbars) combined with its yellow underparts with unique dark necklace, and distinctive face pattern help distinguish this species (in all plumages) from all other species. Note contrasting white undertail coverts, and grayish tail lacking 'tail spots'. Juvenile may resemble juvenile Wilson's Warbler (Wilsonia pusilla) and is best identified by association with adults (8). Adult occasionally confused with Kentucky Warbler (Oporornis formosus), which has a similar overall plumage pattern, but Kentucky Warbler has olive upperparts, yellow undertail coverts, and lacks the black "necklace" shown by the Canada Warbler. For additional information see Dunn and Garrett (8).
Song is a sweet, rich, loud, and distinctive series of jumbled warbling notes often preceded by a loud chip note (see Sounds and Vocal Behavior: Vocalizations).
Canada Warbler has 9 functional primaries (numbered distally, p1 to p9), 9 secondaries (numbered proximally, s1 to s9, including 3 tertials, s7 to s9 in passerines), and 12 rectrices (numbered distally, r1 to r6, on each side of the tail). Little or no geographic variation in appearance (see Systematics: Geographic Variation) or molt strategies reported.
See Molts for terminology on molts and plumages. Following based on published plumage descriptions (9, 10, 11, 12, 13, 14, 15, 4, 16, 8); for specific age/sex-related criteria, see Robbins (17), Riggins and Riggins (18), Rappole (7), and Pyle (19). Appearances of sexes similar in Juvenile Plumage and thereafter show gradual variation across ages, sexes, and seasons, differing slightly in Formative Plumage and more substantially in subsequent plumages, and being brightest in Definitive Alternate males and dullest in Formative females. Definitive appearance assumed at Second Basic Plumage, although there is much individual variation (see Definitive Alternate Plumage).
Present primarily June–July, in the nest. Hatchlings lightly covered with sepia-brown natal down (9).
Juvenile (First Basic) Plumage
Present primarily July–August. Upperparts drab brown or grayish brown; sides of head and neck pale buff brown, wood brown, or olive brown; eye ring pale buff or off-white; upperwing coverts olive-brown, the median and greater coverts broadly tipped with dull vinaceous buff, forming two obscure to conspicuous buffy wingbars; flight feathers as in Formative Plumage (below) but fresher; throat between isabella color and saccardo umber; remainder of underparts dull yellow, washed with pale wood brown or olive brown on throat, breast, and flanks; undertail coverts whitish. See photographs in Pyle (20). Plumage ephemeral and variation not well described; see Pyle (20) for discussion of Juvenile Plumage in warblers. Sexes alike.
Male. Similar to Definitive Basic female but upperparts averaging more grayish and often with concealed black spots on forehead or anterior part of crown; necklace spots average blacker. Much duller than Definitive Basic male: forehead and anterior part of crown washed more heavily with yellow or buffy brown; black on forehead and crown less extensive; remainder of upperparts washed more with olive-green; yellow of underparts duller and more greenish, the necklace spots duller, less sharply defined, and dark grayish to dull blackish instead of black.
Female. Similar to Definitive Basic female, but duller: forehead often yellowish olive; remainder of upperparts more brownish or olivaceous, particularly on crown and back; necklace spots on breast smaller, less numerous, and sometimes extremely pale, appearing as a grayish wash at a distance (16).
In both sexes, Formative Plumage further distinguished from Definitive Basic Plumage by molt limits between replaced formative, grayish blue upperwing greater coverts, contrasting with older, more faded, and greener to brownish-green retained juvenile primary coverts; retained juvenile outer primaries and rectrices thinner, more pointed, browner, and relatively more worn (19).
First Alternate Plumage
Present primarily March–August.
Male. Similar to Definitive Alternate male except averages duller overall: upperparts often tinged olive; black feather centers on forecrown sometimes more restricted; black area on upper cheek and lower side of neck averages narrower; black necklace on breast narrower (6–11 mm), often less sharply defined at rear, where black spots often grade into smaller dark or pale olive spots. New crown feathers contrast with worn feathers in occipital area.
Female. Similar to Definitive Alternate female, but upperparts tinged green; forecrown with fewer or no black on feathers; face pattern less distinct; necklace on breast blackish, often restricted to some spots on side.
In both sexes, criteria to separate First Alternate Plumage from Definitive Alternate Plumage based on wing and tail feathers similar to that described under Formative Plumage and Definitive Basic Plumage, but contrast often even more distinct due to greater rates of wear for juvenile than formative feathers.
Definitive Basic Plumage
Present primarily September–March.
Male. Forehead and crown blackish to dark slate-gray, the feathers broadly edged with neutral gray when fresh; remainder of upperparts neutral gray, mouse gray, or dark bluish gray, the feathers fringed olive when fresh; tail grayish black or chateura drab, the rectrices narrowly edged on outer webs with gray or dark blue-gray of upperparts (faint or absent on outermost rectrix). Lores and lower auriculars, extending to submalar and lower side of neck, blackish; short, bright sulphur-yellow supraloral stripe from nostril to just above front corner of eye; broad and conspicuous white to lemon-yellow eye ring, often yellower above eye; rear auriculars and sides of neck bluish gray, similar to back. Upperwing coverts bluish gray, the centers of the lesser and median coverts and inner webs of the greater coverts grayish black; remiges, tertials, primary coverts, and alula grayish black, fringed along outer webs with bluish gray, slightly darker and wider but less sharply defined in secondaries and tertials, the primaries also margined on inner webs, except at tips, with light brown and the secondaries also with inner edges dull vinaceous buff. Underparts from chin to vent dull lemon-yellow to gamboge yellow; sides of throat to sides of breast with sparse small dusky marks; breast with longitudinal rows of dull black to chateura-black, rounded or triangular spots, the feathers fringed with yellow when fresh obscuring necklace; sides and flanks washed greenish olive when fresh; undertail coverts white (faintly yellow when fresh); underwing coverts and axillaries white, yellowish white, or pale gray, darker gray towards bases; axillaries and lesser coverts tipped yellow.
Female. Crown and forehead gray washed yellowish or olive (sometimes with some obscured black flecks); remainder of upperparts bluish gray, the feathers fringed olive when fresh; wing and tail feathers similar to male, but slightly duller gray and with fringes of flight-feathers sometimes tinged green. Lores and thin stripe along lower auriculars dusky, not as extensive or black as in male; short, dull yellow supraloral stripe in front of eye duller than in male; broad and conspicuous dull white to yellowish eye ring; rear auriculars and sides of neck bluish gray, tinged olive. Underparts similar to male, but sides of throat and chest with single row or no smaller dusky marks; necklace more restricted and with distinct olive, grayish or grayish-black streaks (but not black), obscured by feather fringes when fresh.
In both sexes, Definitive Basic Plumage further separated from Formative Plumage by having upperwing and tail feathers uniform in quality and freshness, dark grayish blue, the primary coverts duskier, edged blue-gray, and not contrasting in feather quality with the greater coverts; basic outer primaries and rectrices broader, more truncate, duskier, and relatively fresher (19).
Definitive Alternate Plumage
Present primarily March–August.
Male. Similar to Definitive Basic male but head and breast plumage bolder and brighter due to wearing of dull fringing and molt. Forehead black, often with short and narrow median stripe of dull lemon yellow; crown also black (or dark slate-gray), feathers narrowly edged with neutral or dark gray imparting a black-spotted appearance; cap thus uniform black in front, heavily spotted black on mid-crown, and marked with smaller spots at rear. Remainder of upperparts dark bluish gray, without olive tinges but sometimes washed deep olive-gray on back and scapulars. Lores and lower auriculars extensively black; yellow supraloral stripe brighter yellow; underparts brighter yellow, the necklace streaks bolder and blacker, each 1–2 mm thick, overall 10–18 mm wide, and becoming solidly black on side of chest.
Female. Similar to Definitive Basic Female but head plumage brighter and better-marked; necklace blacker and more distinctly defined. Substantial variation within plumage classes in forehead, crown, cheek, side of neck, and necklace color for both sexes (7). In particular, wide age-independent variation in necklace color and pattern in both males and females (7; Figure 8.3 in Morse ). In both sexes, criteria to separate First Alternate Plumage from Definitive Alternate Plumage, based on upperwing feathers and rectrices, similar to that described under Formative Plumage and Definitive Basic Plumage.
Molt and plumage terminology follows Humphrey and Parkes (21), as modified by Howell et al. (22, 24). Canada Warbler exhibits a Complex Alternate Strategy (cf. 22, 25), including complete prebasic molts, a partial preformative molt, and limited-to-partial prealternate molts in both first and definitive cycles (26, 9, 15, 7, 4, 16, 8, 19, 27; Figure 1).
Prejuvenile (First Prebasic) Molt
Complete, primarily June–July, in the nest. Most of the feather development occurs after day 4 and pin feathers on the wings are not exposed until day 5 or 6. Otherwise, no information on sequence of pennaceous feather irruption and development. Duration of Prejuvenile Molt among individuals probably 7–9 days as in other New World warblers; near-completed by fledging at day 8, with growth of remiges and rectrices not completing until 3–4 days post fledging.
"First Prebasic" or "Prebasic I" Molt of Humphrey and Parkes (21) and some later authors; see revision by Howell et al. (22). Partial, primarily July (Figure 1), likely commencing in nest and completing shortly after fledging, on breeding grounds. Includes most or all body feathers and upperwing secondary coverts, but not the greater alula and no primary coverts, primaries, secondaries, or rectrices (19, 27).
First Prealternate and Definitive Prealternate Molts
Limited, March–May (Figure 1), on non-breeding grounds. Includes most to all feathers of head, a few to some feathers of the upperparts and underparts, and (in ~15% of birds) 1–3 upperwing greater coverts, especially during the First Prealternate Molt (19, 27). First Prealternate and Definitive Prealternate molts are otherwise similar in timing and extent, as far as known. Reports that Prealternate Molts can begin as early as January on nonbreeding grounds (19) require confirmation; limited body-feather replacement at this time may instead be adventitious or part of protracted/suspended Preformative Molt and Prebasic Molt.
Definitive Prebasic Molt
Complete, primarily July–September (Figure 1), on or near breeding grounds, although study needed on the relationship between breeding territories and molting grounds. Primaries replaced distally (p1 to p9), secondaries likely replaced proximally from s1 and bilaterally from the central tertial (s8), as typical of passerines, and rectrices probably replaced distally (r1 to r6) on each side of tail, with some variation in sequence possible.
Bill and Gape
Short, straight, relatively wide bill with decurved tip of culmen forming small hook; bill approximately half the length of head. In juvenile, pinkish-buff becoming dusky or dull pale brown (9). In adult, upper mandible plumbeous gray, brown, grayish, brownish black, or black; cutting edges and tip of lower mandible bluish gray or horn-gray; remainder of lower mandible lighter: dull pink-white, pinkish brown, pale vinaceous drab, or yellow (12, 4). Rictal bristles long and well developed; 3 strong bristles projecting forward from each side of base of upper mandible. Tongue white.
In juvenile, dark brown. In adult, hazel to clove brown or deep brown.
Legs and Feet
In juvenile, pinkish buff becoming dusky or dull pale brown (9). In adult, pinkish brown, yellowish brown, buffish pink, tan-yellow, clay, yellowish clay, pale yellow, pale tawny olive, light ochraceous drab, or pale grayish yellow (15, 4). Leg color lighter (Munsell color value of 8) than 26 other wood warblers (28).
See Table 1. Many skeletal and other morphological measurements are given in Ostroff (3). Males significantly larger than females based on body mass, tarsus length, tail length, and wing chord (Table 1; 4; F. Moore and D. Cimprich, unpublished data). Wings of males average 5–6% longer than females; males generally > 64 mm and females < 62 mm but considerable overlap exists (7).
Bill Length, Exposed Culmen
Mean 8.87 mm ± 1.09 SD (range 7–11, n = 16; North Carolina State Museum). Males, mean 10.7 mm (range 10.2–11.2); females, mean 10.7 mm (range 9.7–11.2; Texas, 15).
Mean 2.94 mm ± 0.85 SD (range 2–4, n = 16; North Carolina State Museum of Natural Science [NCSMNS]).
Females, mean 52.2 mm ± 3.0 SD (range 45–61, n = 36; S. Morris, personal communication); mean 52.8 mm (range 51.1–53.3; Texas, 15). Males, mean 53.5 mm ± 2.5 SD (range 44.5–59, n = 47; Maine, S. Morris, personal communication); mean 56.1 mm (range 54.8–57.2; Texas, 15).
Middle Toe Without Claw
Males, mean 11.2 mm (range 10.7–11.7); females, mean 10.7 mm (range 9.1–11.7; Texas, 15).
Typically 5.5 × 4 mm during breeding season (museum skins from NCSMNS, ROM, Carnegie Museum of Natural History).
Mean 185.5 mm ± 15.8 SD (range 154–197, n = 8) (15; museum skins from NCSMNS, ROM, UNSM, Cornell University Museum of Vertebrates).
See Table 1. Fall migrants in Illinois and Alabama average heavier than fall migrants in Maine and breeders in North Carolina. Males average 4–11% heavier than females.