Plumages, Molts, and Structure

The appearance of the nominate subspecies from southern Mexico (Snow 1979) is described here for comparative use below to characterize Geographic Variation and subspecies in Rose-throated Becards. The description depends heavily on Ridgway (1907). Oberholser (1974) provided the only other detailed description of a population of this species, that of P. a. gravis, which is found in southeastern Texas and northeastern Mexico. P. a. aglaiae occupies a central position in the range of Rose-throated Becards, where two other subspecies are in direct contact with it and four others are nearby in the region. Its appearance exhibits no extreme characteristics, and thus it offers a convenient standard for a synopsis of other subspecies (Webster 1963).

Adults are sexually dichromatic in all populations. The outer wing is 'slotted' in adult males by a conspicuously shortened and emarginated ninth primary, a characteristic that is shared in several other species of becards once placed in the genus "Platypsaris"(Ridgway 1907).

Adult male: Crown and nape black becoming more sooty anteriorly and gray on forehead; lores grayish to dusky gray, and auriculars slaty, more grayish to brownish below eye and on malar region; upperparts from back to uppertail coverts and upper wing coverts uniform slaty to slaty gray, abruptly contrasting with glossy black cap on crown and nape; greater coverts margined indistinctly with paler gray tone; remiges dull slate or dark brownish gray with paler slate gray outer margins, most noticeable on secondaries, and narrowly edged white on inner webs; rectrices dark slate edged with paler slaty-gray; chin and uppermost throat pale gray to grayish white, while most of throat ruby to rose (Webster 1963), the color sometimes invading upper chest; rest of underparts medium gray becoming paler across abdomen, vent, and undertail coverts, the last quite whitish; axillars and underwing coverts pale brownish gray, sometimes with a buffy tinge. Bill, legs, and feet dark with bluish tone in life, but latter color fades in specimens; irides brown.

Adult female: Crown, nape slaty to dull dusky slate, sometimes suffused with buff tone or buffy streaking, paler on forehead where buff may dominate; hindneck buff, tawny, or ochre producing effect of a variably distinct collar; upperparts from back and wing coverts to uppertail coverts variably light grayish- or brownish buff to buffy, cinnamon, and russet; auriculars, lower throat, chest, and sides strongly buff with reddish tone, becoming buffy white on chin and upper throat, and paler buff posteriorly; axillars and underwing coverts also buffy to ochraceous; bill, legs, feet, and irides as in adult male.

Juveniles and older first year birds: Not described for nominate aglaiae, although juvenile plumages of males and females are similar to one another, and apparently more or less similar to females in their first winter plumage following the conventional first prebasic molt (Stiles and Skutch 1989, Pyle 1997a, Hawkins 2012). Dickey and van Rossem (1938) described the juvenile plumage of becards in El Salvador, where P. a. sumichrasti and P. a. latirostris occur, as "identical in coloration" to variant forms of adult females with black heads. Juvenile males of P. a. gravis were characterized by Oberholser (1974) in error as "Similar to nuptial adult male", but his account also described the male in first winter plumage as "Similar to nuptial adult female", except crown blacker, upperparts darker and more grayish-brown, underparts lighter and more grayish buff, and throat often light salmon pink. The latter description coincides almost verbatim to that of Dickey and van Rossem (1938) for first winter becards farther south. Pyle (1997a) noted that juveniles of the two northernmost subspecies resemble first cycle, post-juvenile females, but upperparts are more rufous and underparts buffier. The extent of geographic variation in juvenile and conventional first basic plumages of the species is unknown. It is clear that delayed plumage maturation occurs in male Rose-throated Becards, at least through the first year of life, and perhaps to some extent to the end of the second annual cycle (Oberholser 1974). Rufous or russet tones are prevalent in the body and wing feathers of males during the first year, and the first few pink or rose feathers may appear then, even rarely at the juvenile stage (Pyle 1997a). Dickey and van Rossem (1938) also suggest that some subtle differences persist into the second-cycle plumage of males although the plumage is very similar to that of adult males. However, such differences may reflect individual variation in a few males rather than a consistent, widespread pattern among males during the second cycle (Webster 1963). Older females, especially in P. a. gravis, also may have a few rose feathers on the upper breast (Pyle 1997a), so sex determination based on these feathers needs confirmation from other characters.

Natal down white (Brandt 1951, Baicich and Harrison 1997). The most recent assessment of molt in Rose-throated Becards is provided by Pyle (1997a, 1997b) in relation to two northern subspecies that enter the United States. A modified and controversial Humphrey-Parkes system of plumage nomenclature currently is being applied to first cycle plumages in becards and tyrannid flycatchers (Howell et al. 2003, Howell 2010, Hawkins 2012). I continue to use the conventional terminology introduced by Humprey and Parkes (1959). Juvenile plumage in Rose-throated Becards is replaced by a partial prebasic (preformative) molt from July–December. The resulting female-like plumage is worn into the second calendar year when a partial pre-alternate molt occurs from March to May. None of the greater secondary coverts, tertials and secondaries, and rectrices are replaced in the first prebasic molt. Up to two greater secondary coverts are replaced in about 44% of individuals during the first pre-alternate molt, and only a few tertials, secondaries, and rectrices are replaced less frequently during this molt (Pyle 1997b). Second and older prebasic molts are complete, and mainly occur on the breeding grounds, or perhaps are completed on wintering grounds in northernmost migratory populations (P. a. gravis, P. a. albiventris). Pre-alternate molts appear to be more prevalent in first spring males than in females of similar age, or in both sexes later in life. The first pre-alternate molt is absent in about 56% of birds, otherwise it is limited to a few greater secondary coverts, and occasionally includes several inner secondaries and one or two central rectrices. Most or all juvenal flight feathers are retained until the second prebasic molt. Pyle (1997a) emphasized the need for further study. This is especially true for Middle American populations of becards. Not known whether geographic patterns of molting exist.

The colors of bare parts notoriously fade with specimen age. Bill, legs, and feet described from specimens as "dusky" or "dark horn color" are often more bluish in life (Ridgway 1907). Colors described on data tags when specimens were fresh (Field Museum of Natural History, Chicago): iris, hazel to dark brown; maxilla bluish gray ("plumbeous") to blackish plumbeous with paler tip; mandible paler varying from dusky flesh to purplish flesh or horn-blue; tarsus plumbeous or blue gray, horn blue, dark blue to lead-blue. Not known to differ among subspecies, but too little information to evaluate the issue.

Ridgway (1907) and Webster (1963) provided measurements in their revisionary works that allow geographic comparisons among populations of Rose-throated Becards. Webster was able to measure all the taxa that we know today, while the northeastern population of P. a. gravis was not recognized as a distinctive named entity in the early twentieth century when Ridgway wrote. Table 1 compiles standard measurements of the taxa known to Ridgway (1907), and Table 2 permits a comparison of means among all currently named taxa (Webster 1963). Some measurements suffer from relatively small sample sizes, especially those of the island form P. a. insularis off western Mexico. No modern statistical analysis of mensural variation across the species’ range is available. I focus on the historically traditional approach of comparison within and among subspecies within what is now recognized as current species limits (see Systematics). I recalculated some means and standard deviations, which had been presented for subpopulations of subspecies, as weighted means for the subspecies concerned (see Table 2). On average, males are larger than females within subspecies (ignoring under-represented P. a. insularis), using wing chord as an index of body size (Table 1). Mean wing length of males was significantly longer than that of females in four of the subspecies (Table 2). Mean values of other characters are similar, larger, or smaller in males than in females in no particular direction. See Geographic Variation for a discussion of measurements in that context.