Cassin's Sparrow

Peucaea cassinii



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Figure 2. Annual cycle of breeding, migration, and molt in se. Arizona.

For Cassin’s Sparrow populations in southeastern Arizona.

Alternate Cassin's Sparrow.

Long-tailed sparrow with indistinct buffy-gray supercilium and pale lemon bend of wing. Tips of outer rectrices are whitish. Bill is long, with relatively straight culmen. When fresh, Formative, Definitive Basic, and Alternate Plumages are similar. But by late summer, Alternate Plumages are noticeably plainer and duller due to feather wear: the upperparts lose their variegated appearance and are almost unstreaked.

© Melissa James , New Mexico , United States , 17 August 2017
Alternate Rufous-morph Cassin's Sparrow.

Rufous morph is brighter overall with more rufous upperparts, wing and tail edgings, and uppertail coverts. The indistinct streaking to the breast sides is a juvenile character that could indicate a first-year. But in this case it more likely represents variation in Alternate Plumage, perhaps due to molt timing that could occur in either first-year or older birds.

© Mark Kosiewski , North Carolina , United States , 1 May 2011
Formative or Definitive Basic Plumage Cassin's Sparrow.

Nape and sides of neck are gray with rufous-brown (some blackish-brown) streaking. Upperwing coverts with grayish to rufous-brown centers, the smaller lesser coverts fringed pale buff to yellowish and the median and greater coverts with buff-gray outer edges, forming indistinct wing-bars. Formative and Definitive Basic Plumages are largely indistinguishable following complete Preformative or Definitive Prebasic Molts, respectively.

© Terry Sohl , Arizona , United States , 10 November 2015
Formative or Definitive Basic Plumage Cassin's Sparrow.

Underparts are pale brown or gray to whitish, the chin with indistinct dark-gray malar stripes, the upper breast darker and washed buff, the sides and flanks paler. Belly is dull white.

© ALAN SCHMIERER , Arizona , United States , 17 January 2017
Formative or Definitive Basic Plumage Cassin's Sparrow.

Formative and basic back feathers and scapulars are pale brown with broad gray edges, dark-brown subterminal spots or irregular bars, and often thin brown shaft streaks or spots, resulting in a variegated pattern of pale gray and warm brown with dark crossbars or spots rather than streaks.

© Paul Suchanek , Arizona , United States , 2 January 2016
Cassin's Sparrow.

Forehead and crown are gray and finely streaked with dark brown. Superciliary stripe is grayish, becoming more pale and buffy above lores (washed pale yellow when fresh); postocular stripe is light cinnamon-brown. Moderately distinct dull white eye-ring is present. Flanks and sides are pale gray and may be striped with a few brown or dusky streaks, especially posteriorly. By this date most birds have commenced the Prealternate Molt and are thus in a transitional plumage.

© Sam Jolly , Texas , United States , 9 March 2018
Cassin's Sparrow tail.

Uppertail coverts are gray brown with narrow pale-gray edges and prominent dark brown subterminal crescent. The central rectrices are brownish gray with a darker serrated shaft streak and imperfectly developed crossbars. The remaining outer rectrices are dusky gray-brown, the outer three with noticeable pale gray to whitish tips (becoming whiter distally) and margins to outer webs, with largest and palest tips to r6. This bird could either be in Formative or Definitive Basic Plumage, which are not separable after the fall molts.

© John & Linda Prentice/Gindler , Texas , United States , 4 February 2018
Auxiliary Formative Cassin's Sparrow.

This is the first of two post-juvenile plumages and results from a partial Auxiliary Preformative Molt, which occurs prior to the complete Preformative Molt. First-fall migrants are often in this plumage. Note that the visible median coverts and some inner greater coverts have been replaced, and contrast in freshness with the remainder of the wing feathers, which are retained juvenile. It also appears that central back feathers may be replaced, contrasting with juvenile scapulars. The underparts are variably streaked in this plumage, usually less so than in Juvenile Plumage.

© Jeff Bray , California , United States , 22 October 2017
Juvenile Cassin's Sparrow.

The throat with short streaks or spots and the breast, sides, and flanks considerably streaked dark brown to brown-gray. Sides of head dull buff, streaked with buffy brown; auriculars and lores margined buff. Underparts are buffy, with paler whitish belly.

© John Drummond , Colorado , United States , 5 April 2018
Cassin's Sparrow chicks in nest.

Chicks are altricial and naked except for sparse, light-gray down on head and back, and pronounced yellow rictal flanges. Mouth lining is dark red with two parallel yellow lines on upper palate and two yellow spots on floor of mouth as feeding targets.

© Felipe Guerrero , Arizona , United States , 20 August 2017

A plain, nondescript sparrow, with body shape typical of the broader definition of Aimophila (in which Cassin’s Sparrow was formerly placed): large bill, elongated body, and a long, rounded tail. Total length 13–15 cm, mass 17–18 g. The bill is long, with a relatively straight culmen. Formative, Definitive (adult) Basic, and Alternate plumages are similar, mostly gray-brown, with a plain face (indistinct gray or buffy-gray supercilium), and gray crown. Bend of wing is pale lemon, and outer rectrices have whitish tips. The less-common rufous morph is brighter overall with more rufous upperparts, wing and tail edgings, and uppertail coverts (20). There are no sexual differences in plumage. Juvenile is similar to later plumages, but buffier and with considerable dark brown streaking on underparts; some Formative birds retain indistinct streaking across breast (a juvenile character retained on formative feathers), this has often worn-off by late summer. In late summer, adult may be very worn, making plumage characteristics such as barring and whitish tips on rectrices even more indistinct.

Similar Species

Botteri's Sparrow (Peucaea botterii) is very similar, but is richer brown and the bill is larger with a thicker base and more curved culmen. Both species are most easily identified in the field by their distinctive male songs, especially the dramatic Flight Song of Cassin's Sparrow. There are several subtle plumage differences that separate Cassin's and Botteri's sparrows, with the following summarized from Kaufman (21). In Cassin's Sparrow, fresh back feathers have gray edges and brown centers with a black crescent or bar, whereas back feathers of Botteri's Sparrow are brownish with central black stripe. The overall effect is that in fresh plumage Cassin's Sparrow appears spotted or scalloped on the upperparts, whereas Botteri's Sparrow appears narrowly streaked. Uppertail coverts in Cassin's Sparrow are tipped with black crescents, and streaked in Botteri's Sparrow. Fresh central rectrices of Cassin's Sparrow are pale gray-brown and faintly barred, contrasting with browner outer rectrices; all rectrices of Botteri's Sparrow are uniformly brown. Outer rectrices of Cassin's Sparrow have large gray or whitish tips, which are lacking in Botteri's Sparrow. Pale rectrix tips of Cassin's Sparrow are sometimes visible in flight (JBD), but wear away by late summer. Other subtle plumage characteristics of Cassin's Sparrow in fresh plumage include a few brown streaks on flanks (not visible when present on Botteri's Sparrow), pale gray breast (buff or grayish buff on Botteri's Sparrow), and tertials with blackish centers and edged with white (brown in Botteri's Sparrow). All of these marks can be altered by wear in late spring and summer, and birds in worn plumage are difficult to separate. Cassin's Sparrow is most similar to the gray texana subspecies of Botteri's Sparrow (22). Bachman's Sparrow (P. aestivalis) is similar in size and shape to Cassin's Sparrow, but upperparts are redder (more chestnut), having reddish-brown crown with little or no streaking (21); in addition, the buffy breast contrasts with a whiter belly, uppertail coverts lack the anchor-shaped markings, and the outer rectrix has pale tip 5–6 mm when fresh (vs. > 15 mm on Cassin's Sparrow) (23). Use care in separation of uncommon rufous morph of Cassin's Sparrow from Bachman's Sparrow. Songs and habitat are the most distinctive traits among the 3 species in the field. In the hand, Cassin's Sparrow shows a medium wing chord (56–68 mm) of the 3 species and shows a longer wing morphology, with p9 > p3 by 3–7 mm and the longest primary to the longest secondary 8–13 mm when feathers fresh and not molting; the bill is also more slender, depth at the tip of the nares being 4.5–5.3 mm (23). Other Aimophila sparrows north of Mexico have rufous cap and 1–2 mustache marks (Rufous-crowned Sparrow [Aimophila ruficeps] and Rufous-winged Sparrow [Peucaea carpalis]) or a strong facial pattern of gray, black and white stripes (Five-striped Sparrow [Amphispiza quinquestriata]). Cassin's Sparrow is much plainer, especially on the head, than all similar Mexican species, except perhaps Oaxaca Sparrow (Aimophila notosticta) and Cinnamon-tailed Sparrow (P. sumichrasti), both of which are found south of the Cassin's Sparrow range (24).

Brewer's Sparrow (Spizella breweri) is also grayish brown with few strong plumage marks and similar measurements for wing and tail length, but it has a much smaller and slimmer build (typical Spizella shape, with small bill and slender, shorter, notched tail). Brewer's Sparrow also has narrow black streaks on crown and back.

Detailed Description

Cassin's Sparrow has 9 functional primaries (numbered distally, p1 to p9), 9 secondaries (numbered proximally, s1 to s9, and 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 or sex-specific variation in appearance (see Systematics: Geographic Variation) or molt strategies has been reported.


The following is based primarily on detailed plumage descriptions of Ridgway (25), Oberholser (20), Wolf (3), Willoughby (10), Byers et al. (26), and Rising (27); see Pyle (23) for specific age-related criteria. Sexes show similar appearance in all plumages. Definitive Appearance is usually assumed at Formative Plumage.

Natal Down

Present primarily April–July, in the nest. Hatchlings with sparse down, restricted to head and back; generally described as “very dark” (20, 28). Schnase (29) characterized the down as “light gray” which is also evident on photographs of nestlings of 2 days in age taken by RKB. Down on head still light gray several days later (RKB).

Juvenile (First Basic) Plumage

Present primarily May–August. Similar to Definitive Alternate plumage but buffier overall, upperparts duller and less variegated, and underparts with dusky brown streaking on breast and flanks. Forehead and crown feathers with dark-brown centers and buff-brown edges forming irregularly streaked appearance; feather edges on nape cream colored, forming pale collar; back dull brown, the feathers with dark-brown central streaks (generally slightly expanded to irregular spots or bars distally), and buffy tips; rump feathers barred and with dull cinnamon-buff tips. Sides of head dull buff, streaked with buffy brown; auriculars and lores margined buff. Upperwing coverts brown with buff fringes, the median coverts tipped grayish buff and greater coverts tipped white, forming two indistinct wing bars; primary coverts and remiges pale brown with thin, buff to whitish margins. Underparts gray-buff to cream-buff, with paler whitish belly and more richly colored undertail coverts, the throat with short streaks or spots and the breast, sides, and the flanks considerably streaked dark brown to brown-gray. Juvenile body feathers (especially undertail coverts) filamentous due to lower barb density than feathers of later plumages.

Auxiliary Formative Plumage

"Supplemental Plumage" of Thompson and Leu (11) and Pyle (23); see revision by Howell et al. (30). Present primarily June–September, often during migration. Similar to Definitive Basic Plumage but breast with dark spotting that varies among individuals from heavy to nearly or entirely absent. Individuals lacking dark spots most reliably distinguished by molt limits between worn juvenile and fresh formative feathers among upperwing and (occasionally) tail (23): upperwing coverts usually mixed, the inner coverts replaced, with rufous-brown or dark brown centers and fringed buff, contrasting with duller and paler brown, retained outer coverts with whitish fringes; 1–3 tertials occasionally replaced, contrasting with older retained juvenile tertials and secondaries; juvenile primary coverts paler brown with reduced whitish edging; 1–2 central rectrices occasionally replaced, contrastingly fresh. A few scattered juvenile body feathers may also remain, most commonly on the neck, occipital region, and nape (10).

Formative Plumage

"First Basic" or "Basic I" plumage of Humphrey and Parkes (31) and later authors; see revision by Howell et al. (30). Present primarily November–February, largely on winter grounds. Formative and Definitive Basic plumages are essentially indistinguishable. Pyle (23) suggested that individuals with one or more breast spots are in Formative rather than Definitive Basic Plumage but reliability of this uncertain; Willoughby (10) found one or more breast spots in 11 of 58 (~20%) Formative/Definitive Basic individuals, with one individual showing heavier spotting as in Auxilliary Formative Plumage.

First and Definitive Alternate Plumages

Present primarily March–September, primarily on breeding grounds. Similar to Definitive Basic Plumage but birds show a mixture of older and abraded Formative or Basic feathers and newer, less worn, and less faded Alternate feathers, resulting in less-uniform coloration, especially of the upperparts. By late summer, Alternate plumages are noticeably plainer and duller due to feather wear: the upperparts lose their variegated appearance and are almost unstreaked (some birds are very scruffy, entirely pale gray-brown above with only indistinct darker spots), the uppertail coverts lose their edgings and subterminal dark crescents, and the pale-gray tips of the outer rectrices may be largely or entirely lost. First and Definitive Alternate plumages are not separable.

Definitive Basic Plumage

Present primarily October–February. Forehead and crown gray, finely streaked with gray-brown and some blackish brown; nape and sides of neck gray with rufous-brown (some blackish-brown) streaking; back feathers and scapulars pale brown with broad gray edges, dark brown subterminal spots or irregular bars, and often thin brown shaft streaks or spots, resulting in a variegated pattern of pale gray and warm brown with dark crossbars or spots rather than streaks; this patterning becomes less developed toward rump. Uppertail coverts gray-brown with narrow pale gray edges and prominent dark brown subterminal crescent; central rectrices (r1) brownish gray with darker serrated shaft streak and imperfectly developed crossbars; remaining outer rectrices dusky gray-brown, the outer 3 feathers (r4–r6) with noticeable pale-gray to whitish tips (becoming whiter distally) and margins to outer webs, with largest and palest tips to r6. Lores and sides of head pale gray to dull buff washed gray, the auriculars gray-buff with fine buffy white streaking and narrow cinnamon-brown rear border; superciliary stripe gray or buffy gray, more pale and buffy above lores; postocular stripe light cinnamon-brown; moderately distinct eye-ring present, dull white. Upperwing coverts with grayish to rufous-brown centers, the smaller lesser coverts fringed pale buff to yellowish and the median and greater coverts with buff-gray outer edges, forming indistinct wing bars; primaries and secondaries dull brown with thin paler outer edges; tertials brown with terminal margins and buff to whitish tips. Underparts pale brown or gray to whitish, the chin with indistinct dark-gray malar stripes, the upper breast darker and washed buff, perhaps occasionally with one or more dark streaks or spots (see Formative Plumage), the sides and flanks paler and sometimes (sides) to usually (flanks, especially posteriorly) with a few brown or dusky streaks; belly dull white; undertail coverts sometimes washed buff. Undersides of remiges and underwing coverts grayish, the marginal lesser coverts along leading edge of underwing cream-buff, becoming yellow distally.

An uncommon rufous "morph" (20) of the Cassin's Sparrow appears to be found more regularly in eastern portion of range: similar to gray morph (above) but hindneck, back and scapulars with larger, more numerous rufous-brown centers; sides of head buffier, sometimes much streaked with dull cinnamon-brown; underparts, especially upper breast, sides, flanks, and crissum, a deeper buff. See Figure 9 in Bevier (32) for a comparison of both morphs. Byers et al. (26) suggest the rufous morph also has plainer tail, with less developed shaft streak and barring on the central rectrices, but this requires confirmation. Some birds may be intermediate between gray and rufous types.



Molt and plumage terminology follows Humphrey and Parkes (31) as modified by Howell et al. (30, 33). Cassin's Sparrow exhibits a Complex Alternate Strategy (cf. 30, 34), including complete prebasic molts, a partial auxiliary preformative molt, complete preformative and prebasic molts, and partial prealternate molts in both first and definitive cycles (20, 3, 10, 11, 35, 23; examination of specimens by SJS; Figure 2). Cassin's Sparrow is one of at least 16 species of North American passerines reported to molt twice in the first 6 mo after fledging (23): shortly after fledgling, juveniles undergo a partial molt (primarily in May–August) which lasts about 2 mo, followed by a complete molt in September through November. Adults have an extended body molt in spring and summer (late February to August), and a rapid complete molt (lasting on average 6 wk) in late August to November. Thus a proportion of individuals within the population may be molting body feathers year-round (10; Figure 2).

Prejuvenile (First Prebasic) Molt

Complete, primarily April–September in North America, in the nest. Sheathed remiges, upperwing coverts, and dorsal and ventral body feathers present by day 3; sheathed rectrices and head feathers by day 5. By day 6–7, all feathers have emerged and young are fluffy except for patches between spinal and vental pterylae (29). Rectrices are short and nearly completely sheathed at fledging at ca. day 8–10 and become fully grown 2 wk later (29).

Auxiliary Preformative Molt

"Presupplemental Molt" of Thompson and Leu (11) and Pyle (23); see revision by Howell et al. (30) regarding the terminology of such unique, second-inserted first-cycle molts, first recognized and described in sparrows and cardinals by Sutton (36) and detailed for Cassin's Sparrow by Willoughby (10). Considerations of timing and extent of molt and the resulting changes in plumage color led Thompson and Leu (11) to consider the second molt after fledging as the Preformative Molt and the earlier molt as an Auxiliary Preformative Molt and this sequence is followed here. Irrespective of plumage color, this terminology presumes that the first post-juvenile molt is the later inserted molt evolutionarily, thus is termed the Auxiliary Preformative Molt, and that the second post-juvenile molt is homologous with Preformative Molts of related and ancestral taxa; the reverse of this, however, is also a possibility. Before recognition of the Auxiliary Preformative Molt, nomenclature for resulting plumages were confused and combined in most published descriptions. Length of breeding season and effects of variation in environmental conditions on timing of breeding complicate efforts to determine temporal patterns of molts from specimens; longitudinal studies of marked birds could provide a better indication of the duration of the different molts and a clarification of their nomenclatural sequence.

Auxiliary Preformative Molt in Cassin's Sparrow partial, primarily May-August (Figure 2), on or near the breeding grounds. Includes most to all body feathers, some to most upperwing secondary coverts and occasionally (in ca. 7% of birds) 1–2 tertials and/or 1–2 central rectrices (10, 35, 23). Molt can begin in midback of dorsal tract and proceeds posteriorly on back and head, with last dorsal regions to molt being cervical area of spinal tract and occipital portion of coronal tract; molt on ventral surfaces begins shortly after start of molt on dorsal surfaces, commencing with breast, sides, and throat, proceeding posteriorly along sides and flanks, then toward midline of abdomen and to area around vent; sides of head replaced late in molt period, starting with superciliary region and auriculars (3).

Preformative Molt

"First Prebasic" or "Prebasic I" Molt of Humphrey and Parkes (31) and some later authors; see revision by Howell et al. (30) and see Auxiliary Preformative Molt (above) for additional notes on the terminology of inserted first-cycle molts. Complete, primarily September–November (Figure 2), variably occurring on or near the breeding grounds or on the winter grounds, and suspending for migration (e.g., after inner primaries have been replaced) in at least some individuals. Light body molt occurring in December-February (10) may be part of protracted Preformative and/or Prebasic Molts. Sequence of body-feather replacement as in Auxiliary Preformative Molt and sequence of flight-feather replacement as in Definitive Prebasic Molt (3, 10). Pyle (23) mentions the possibility that some birds may retain juvenile middle secondaries and/or primary coverts but confirmation needed.

First and Definitive Prealternate Molts

Partial, primarily March–July (Figure 2), often commencing on non-breeding grounds and completing on breeding grounds; molt continues at low levels through nesting period but appears to suspend for peak breeding and resume between broods; molt timing variable depending on breeding dynamics (10). The Prealternate Molts include some to most body feathers (sometimes confined to head and throat), sometimes (in ca. 20% of individuals) 1-3 tertials and occasionally (in ca. 5% of individuals) 1–2 central rectrices (10, 35, 23). First and Definitive Prealternate Molts are similar in timing and extent, as far as known.

Definitive Prebasic Molt

Complete, primarily August–October (Figure 2), primarily on non-breeding grounds though it may commence on or near breeding grounds in some individuals (study needed); some individuals may undergo molt migration in July–August to North American Monsoon region of Arizona, and northwestern Mexico before continuing to winter grounds, as documented in other passerines (37, 38). Prebasic Molt may last on average 1.5 mo in individuals (10). Primaries (and corresponding primary coverts) are replaced distally (p1 to p9), secondaries are replaced proximally from s1 and proximally and distally from the central tertial (s8), and rectrices are generally replaced distally (r1 to r6) on each side of tail, with some variation in sequence. Body molt begins at or shortly before start of molt of primaries, and is completed by late stages of replacement of primaries; some birds begin replacement of tertials before replacement of p1, others not until after p3 is partly regrown; upperwing greater coverts are replaced by the time p5 is replaced, with other coverts lost later; replacement of rectrices begins sometime during molt of p1–p5 and ends during molt of p6–p9 (3).

Bare Parts

Bill and Gape

At hatching, bill brownish gray with prominent yellow gape flanges. Dark red lining with 2 parallel yellow lines along midline of upper palate and a pair of yellow spots on floor of the mouth (29). Subsequently, upper mandible becomes dark gray-brown with paler gray tomial edge, lower mandible same bluish gray, grading to paler, whiter shade at base. At 2 days of age, skin of nestlings is orangish pink, and by age 4–5 d skin much darker (from photographs taken by RKB).


Dark brown.

Legs and Feet

Variously described as light brown or dark pinkish; photos by RKB show pinkish-brown. Oberholser (20) noted darker claws, also evident in RKB photos.

Linear Measurements

Males average slightly larger than females. Data not adequate for comparisons across range. Mean measurements of birds (both sexes) banded year-round in southeastern Arizona (39): wing length (chord), 63.0 mm ± 2.4 SD, (range 56–68, n = 102). Exposed culmen (from base of feathers on proximal portion of bill to tip of upper mandible), 12.0 mm (range 12.0–12.0, n = 4).

From Wolf (3), mean measurements of museum specimens: Bill length (anterior edge of nares to tip): male, 7.68 mm ± 0.36 SD (range 6.8–8.3, n = 44); female, 7.48 mm ± 0.28 SD (range 7.0–8.2, n = 37). Bill depth: male, 4.92 mm ± 0.16 SD (range 4.5–5.5, n = 38); female, 4.87 mm ± 0.16 SD (range 4.5–5.1, n = 25). Bill width: both sexes 3.9 mm ± 0.21 SD (range 3.4–4.3, n = 82). Wing-chord length: male, 63.8 mm ± 1.23 SD (range 61.6–67.3, n = 43); female, 62.0 mm ± 1.69 SD (range 58.8–65.6, n = 16). Tail length: male, 67.8 mm ± 2.17 SD (range 63.9–71.0, n = 13); female, 66.4 mm ± 2.5 SD (range 62.0–71.2, n = 13). Tarsus length: both sexes, 19.8 mm ± 0.63 SD (range 18.5–21.4, n = 82). Middle toe length: both sexes, 14.3 mm ± 0.4 SD (range 13.5–16.1, n = 66). Hallux: both sexes, 10.6 mm ± 0.33 SD (range 9.9–11.6, n = 66).

Wing-tip shape is elliptical and wings are somewhat longer than expected from wing length: body size ratio (3). The elliptical shape is expected of migratory species, where wing-tips are more pointed than in sedentary forms. Neither Botteri's Sparrow nor Bachman's Sparrow has long wings. Wing length is the least variable trait within the Aimophila as formerly defined (shown by analysis of coefficient of variation); tail length and tarsus length are the next least variable (3).

Tail length is relatively short compared to rest of former genus. Length of hallux, middle toe, and tarsus are highly correlated with body weight within formerly defined Aimophila. Cassin's Sparrow and Botteri's Sparrow have a relatively small, weak bill (long for its depth) compared to rest of the formerly defined genus.


From Dunning and Bowers (39), mean mass of birds (both sexes) banded year-round in southeastern Arizona was 18.3 g ± 2.9 SD (range 16.0–21.5, n = 125). Mean mass of breeding birds (July–September) in southeastern Arizona (RKB): male, 17.8 g ± 1.19 SD (range 16.0–19.5, n = 28); female, 18.1 g ± 1.25 SD (range 16.0–21.5, n = 15). From Deviche et al. (40), mean mass of breeding adult males (July–August) in southern Arizona was 17.8 g ± 1.0 SD (n = 40). From Wolf (3), mean mass of museum specimens: male 17.6 g ± 1.0 SD (range 16.0–19.5, n = 20); female, 18.8 g (range 17.5–19.8, n = 5).

Recommended Citation

Dunning, J. B., Jr., R. K. Bowers Jr., S. J. Suter, and C. E. Bock (2018). Cassin's Sparrow (Peucaea cassinii), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.