Phenotypic and vocal variation is marked throughout this species’ wide geographic range. Phenotypic variation is largely clinal from northern Mexico south through Central America to northwestern South America, with birds becoming smaller and paler southward (and out the Yucatan Peninsula). Size peaks in Amazonia, with birds in arid northeastern Brazil and on the Pacific Coast west of the Andes of moderate size; by contrast, birds in the Atlantic Forest are small. Birds throughout Middle America and much of Amazonia are olive, with birds in Amazonia more uniformly olive and those in Middle America having a contrasting brown mantle. Birds on the Pacific coast of Ecuador and Peru has the wings and tail pale tawny rather the deep rufous, birds in arid northeastern Brazil are brown and cinnamon overall rather than olive, and birds in the Atlantic Forest and in eastern Brazil are predominantly yellow rather than olive. Voice also varies geographically, generally being either a staccato trill (Middle America and northwestern South America) or a series of thin whistles (see Systematics and Vocalizations).
Fifteen subspecies in five groups, which differ in plumage color, body size, and bill size (Marantz et al. 2003). Despite marked differences in coloration among subspecies groups, subspecies within a group are similar to each other. Principal songs also differ among some of the groups (see Vocalizations).
griseus group – Middle America and northern South America (size small to moderate; bill short; olive overall but mantle contrasting brown; wings and tail rufous; wing band whitish or buff)
S. g. jaliscensis Nelson, 1900. Includes S. g. harrisoni Sutton, 1955. Resident in Mexico north of the Isthmus of Tehuantepec, in the Sierra Madre Occidental north to southern Nayarit and in the Sierra Madre Oriental north to eeastern San Luis Potosí and central Tamaulipas. Like S. g. sylvioides but dorsum darker and body size larger. Sutton (1955) reported birds intermediate between S. g. jaliscensis (as defined here) and S. g. sylvioides in Puebla.
S. g. sylvioides Lafresnaye, 1850. Includes S. pectinicaudus Reichenbach, 1853; S. levis Bangs, 1902; S. g. veraguensis Aldrich, 1937; and S. g. enochrus Wetmore, 1970. Resident in southern Mexico south of the Isthmus of Tehuantepec (north to southern Veracruz and southeastern Oaxaca) and south on both slopes through Central America to northwestern Colombia (northern Córdoba and northern Bolívar) [type locality = “Mexico”]. Like S. g. griseus but wing band buff, overall coloration darker and grayer (less green), and mantle rustier.
S. g. gracileus Bangs and Peters, 1928. Resident on the Yucatan Peninsula, south to eastern Tabasco, northern Guatemala (Petén), and northern Belize [type locality = Chichén Itzá, Yucatán, Mexico]. Like S. g. sylvioides but paler and smaller overall (Figure 2; see Paynter 1955 for size data). Birds in southern Belize are intermediate toward S. g. sylvioides (Austin 1929).
S. g. perijanus Phelps and Gilliard, 1940. Resident in northeastern Colombia (northwestern. Magdalena, western Guajira), and northwestern Venezuela (Sierra de Perijá, western Zulia) [type locality = La Sabana, Río Negro, Perijá, Venezuela]. Like S. g. griseus but wing band buff, head more olive (less green), and mantle more brown (less olive).
S. g. tachirensis Phelps and Phelps, 1956. Resident in northern Colombia (southern Bolívar and Santander) and western Venezuela (southwestern Táchira) [type locality = Cerro El Teteo, Burgua, Táchira, Venezuela]. Like S. g. perijanus but more olive overall and rump darker and more reddish (less orangish).
S. g. griseus Jardine, 1847. Includes S. phelpsi Chapman, 1897; and S. g. virescens Hellmayr and Seilern, 1912. Resident on both slopes of eastern Andes and in coast ranges of northern and northeastern Venezuela (southwestern Barinas and Mérida north to northwestern Lara and central Falcón east to Sucre and northern Monagas); also resident on Tobago (but not Trinidad) [type locality = Tobago]. Similar to S. g. griseicapillus but smaller, bill shorter, head and vent more greenish olive, mantle brown (contrasting with head), band at base of remiges whitish and narrow (especially on secondaries). Hellmayr (1925) noted that “certain specimens” of S. g. amazonus “closely approach” characters of S. g. griseus “in the very pale hue of the wing band.”
aequatorialis group – Pacific slope of Ecuador and Peru (size moderate; bill moderate; olive overall, but mantle contrasting brown; wings and tail tawny; wing band tawny)
S. g. aequatorialis Ridgway, 1891. Resident on Pacific slope of northwestern South America, from western Ecuador (north to western Esmeraldas) south to northwestern Peru (Tumbes) [type locality = Guayaquil, Ecuador]. Most similar to S. g. grisceus group but mantle fulvous brown (less olive) and wings and tail pale tawny (not rufous).
griseicapillus group – Amazonia and Chaco (size large; bill long; olive overall; wings and tail rufous; wing band tawny)
S. g. amazonus Lafresnaye, 1850. Resident in western Amazonia on both banks of the Amazon River, from southeastern Colombia (north to southern Meta, Vichada, and Guainía), southern Venezuela (western and southern Amazonas), eastern Ecuador, eastern Peru, and northern and western Brazil, east to the Rios Negro and Madeira and south to northwestern Mato Grosso [type locality = “Upper Amazon,” Peru]. Like S. g. grisceicapillus but body plumage darker and grayer (less olive), axillaries and underwing coverts whitish, remiges and rectrices more rufescent; bill averages larger. Birds from the upper Rio Madeira are paler and more olive and thus intermediate toward S. s. griseicapillus (Hellmayr 1925); moreover, a specimen from Chapada, Mato Grosso, is intermediate in color and size between S. g. amazonus and S. g. griseicapillus.
S. g. viridis Carriker, 1935. Includes S. g. viridior Todd, 1948. Resident in Amazonian Bolivia (Beni, La Paz, Cochabamba, and northern and eastern Santa Cruz) [type locality = Santa Ana, Río Coroico, La Paz]. Like S. g. grisceicapillus but dorsum more olive-green and ventrum distinctly paler, more yellowish green to buffy-olive.
S. g. axillaris Zimmer, 1934. Includes S. g. sordidus Todd, 1948. Resident in northeastern Amazonia north of the Amazon River, from southeastern Venezuela (northern and central Amazonas and Bolívar) and lower Rio Negro east to French Guiana and north-central Brazil (Amapá) [type locality = São José, Rio Jamundá, Brazil]; apparently unrecorded in Suriname, although it likely occurs there. Similar to S. g. amazonus but axillars and underwing coverts ochraceous, outer edge of outer remiges more rufescent, and mantle more strongly rufescent; size averages slightly smaller.
S. g. transitivus Pinto and Camargo, 1948. Resident in southeastern Amazonian Brazil south of the Amazon River and east of the RioTapajós south to northeastern Mato Grosso [type locality = Chavantina, Rio das Mortes, Mato Grosso]; this subspecies may also occur between the Rios Madeira and Tapajós (Marantz et al. 2003), but Zimmer (1934) treated birds in this area as S. g. amazonus. Phenotype intermediate between S. g. griseicapillus and S. g. axillaris, although more like the former but with upperparts grayer and wing-band more richly cinnamon than axillaries.
S. g. griseicapillus (Vieillot, 1818). Includes S. chapadensis Ridgway, 1891. Resident in south-central South America from southeastern Bolivia (southern Santa Cruz southwest to Tarija) east across central Brazil (southwestern Mato Grosso and Mato Grosso do Sul) and south through western Paraguay to north-central Argentina (Catamarca, Santiago del Estero, and northern Santa Fe) [type locality = Concepción del Paraguay, Paraguay, fide Hellmayr 1925]. Large; hindcrown olive-brown, head and mantle olivaceous, ventrum grayish or olive-buff, flanks buff, axillaries ochraceous buff, band at base of remiges tawny, and retrices and remiges rufous.
reiseri group – arid northeastern Brazil (size moderate; bill short; brownish overall; wing band buff)
S. g. reiseri Hellmayr, 1917. Includes S. g. cearensis Cory, 1921. Resident in northeastern Brazil (southern Maranhão, Ceará, and Pernambuco south to Tocantins and northern and western Bahia) [type locality = Pedrinha, west shore of Lake Parnaguá, Piauí]. Similar to S. g. grisceicapillus but hindcrown cinnamon-brown, head and mantle cinnamon-brown, ventrum cinnamon-buff, flanks cinnamon, axillars ochraceous, and remiges and rectrices pale, rich rufous; averages smaller overall, with the bill averaging shorter and more slender. Hellmayr (1925) reported a specimen “somewhat intermediate to S. g. griseicapillus.”
sylviellus group – Atlantic Forest and eastern Brazil (size small; bill small; olive-yellow overall; wing band buff)
S. g. olivaceus Wied, 1831. Resident along coast of eastern Brazil (southeastern Bahia) [type locality = eastern Brazil]. Like S. g. syviellus, but more olive (less yellow) overall, with ventrum duller.
S. g. sylviellus (Temminck, 1821). Includes S. erithacus (Lichtenstein, 1822); S. temminckii Lesson, 1830; and Acanthurus microrhynchus Bertoni, 1901. Resident in Atlantic Forest from southeastern and southern Brazil (northern Goiás, Minas Gerais, and Espírito Santo) to southeastern Paraguay, northeastern Argentina (Misiones and northeastern Corrientes), and northeastern Uruguay [type locality = Rio de Janeiro, Hellmayr 1925]. Head and mantle olivaceous mustard yellow, ventrum ochraceous yellow, and rectrices and remiges deep rufous; size small.