White-throated Thrush Turdus assimilis Scientific name definitions

While most authorities currently regard this as a separate species from the exclusively South American White-necked Thrush (Turdus albicollis), some take an even more expansive view and split the form found from easternmost Panama to northwest Ecuador as a third species, the Dagua Thrush (Turdus daguae). As constituted here, however, the White-throated Thrush is found from northern Mexico (close to the US border) south to northwest Ecuador; its range encompasses both the Pacific and Caribbean slopes of Middle America, where it inhabits a wide range of forest types. It usually prefers fairly dense cover, and is seemingly rarely seen in the open. The bird’s plumage is mainly dark brown over the head and upperparts, with paler, slightly buffier brown underparts, becoming whiter posteriorly, with a clean but narrow white band on the foreneck and a heavily dark-streaked throat. As many as 14 different subspecies are recognized within this species.

22–26 cm; 62–87 g. Nominate race has grayish-brown to brown head and upperparts, white throat heavily streaked with dark brown meeting short white collar on upper breast, buffy to peach wash on breast and flanks, white belly to vent; narrow yellow eyering; bill yellowish at base; legs yellowish gray. Sexes similar. Juvenile is like adult but with pale cinnamon streaks on upperparts, whitish to buffy underparts with brown spotting and mottling.

Until recently considered to form a subspecies group of T. albicollis. Differs, however, in plumage, with overall browner-grey underparts (1), slightly darker on breast (1), and variably “colder” (grayer or more olive) upperparts (ns); and strongly in voice, song being delivered at a steady pace, typically changing notes all the time, but many repeated 2–3 times, most notes in range 1.5–3.5 kHz, occasionally higher, vs a continuous slow series (“caroling”) of throaty whistles at rather flat pitch, thus present species singing at a higher pace (score 2), with shorter, more variable notes (ns[2]) but often with 2–4 repeats (3) and in larger frequency range (ns[2]) (1 Boesman, P. (2016). Notes on the vocalizations of White-throated Thrush (Turdus albicollis). HBW Alive Ornithological Note 305. In: Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. Close ). Number of races surprisingly high, given modest levels of differentiation, and thorough revision needed; proposed race oblitus (from Costa Rica) merged with leucauchen.

Subspecies differ primarily in color tones (see below).

Eleven subspecies recognized here, but the lack of clear plumage differences suggests the need for a careful revision of the group. Subspecies daguae has been given separate species status (2 Ridgely, R. S., and P. J. Greenfield (2001). The Birds of Ecuador. Volumes 1 and 2. Cornell University Press, Ithaca, NY, USA. Close , 3 Núñez-Zapata, J., Peterson, A.T. and Navarro-Sigüenza, A.G. (2016). Pleistocene diversification and speciation of White-throated Thrush (Turdus assimilis; Aves: Turdidae). Journal of Ornithology. 157(4): 1073–1085. Close ) or assigned to T. albicollis (4 Collar, N., J. S. Marks and G. M. Kirwan (2019). White-necked Thrush (Turdus albicollis). In Handbook of the Birds of the World Alive (del Hoyo, J., A. Elliott, J. Sargatal, D. A. Christie and E. de Juana), Lynx Edicions, Barcelona, Spain. Close ).

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EBIRD GROUP (POLYTYPIC)

White-throated Thrush (White-throated) Turdus assimilis [assimilis Group]

Available illustrations of subspecies in this group

• eBird map
• 121 photos
• 100 recordings

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SUBSPECIES

Turdus assimilis calliphthongus Scientific name definitions

Distribution

NW Mexico (SE Sonora to NE Sinaloa and SW Chihuahua).

Identification Summary

T. a. calliphthongus is paler above and below than nominate.

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SUBSPECIES

Turdus assimilis lygrus Scientific name definitions

Distribution

W Mexico (s Sinaloa to w Oaxaca and sw Chiapas)

Identification Summary

T. a. lygrus is like calliphthongus but slightly more rufous above.

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SUBSPECIES

Turdus assimilis assimilis Scientific name definitions

Distribution

C Mexico (E Hidalgo and W Veracruz S to N Oaxaca).

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SUBSPECIES

Turdus assimilis oaxacae Scientific name definitions

Distribution

Highlands of Oaxaca

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SUBSPECIES

Turdus assimilis leucauchen Scientific name definitions

Distribution

S Mexico (s Veracruz) to Honduras

Identification Summary

T. a. leucauchen is like nominate but darker and blacker above, more contrasting white collar , slight peachy wash on flanks, brighter orange-yellow bill, eyering and legs.

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SUBSPECIES

Turdus assimilis rubicundus Scientific name definitions

Distribution

Pacific slope of SE Mexico (S Chiapas), W Guatemala and El Salvador.

Identification Summary

T. a. rubicundus is dull olive on breast and flanks.

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SUBSPECIES

Turdus assimilis atrotinctus Scientific name definitions

Distribution

E Honduras and N Nicaragua.

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SUBSPECIES

Turdus assimilis oblitus Scientific name definitions

Distribution

Highlands of n and central Costa Rica

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SUBSPECIES

Turdus assimilis cnephosus Scientific name definitions

Distribution

SW Costa Rica and W Panama.

Identification Summary

T. a. cnephosus is similar to nominate but warmer on breast and flanks.

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SUBSPECIES

Turdus assimilis coibensis Scientific name definitions

Distribution

Coiba I and associated islets (off S Panama).

Identification Summary

T. a. coibensis is small and dark.

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EBIRD GROUP (MONOTYPIC)

White-throated Thrush (Dagua) Turdus assimilis daguae Scientific name definitions

• eBird map
• 13 photos
• 10 recordings

Distribution

E Panama S to NW Ecuador.

Identification Summary

The Choco bioregion form, daguae, has a shorter bill, rusty-brown tinge above, and brownish-gray legs.

Northwest Mexico (southeastern Sonora), through Middle America and northwestern Colombia to northwestern Ecuador.

Often confined to forest but also uses forest edge, brushy thickets and second growth (5 Sekercioglu, C.H., Loarie, S.R., Brenes, F.O., Ehrlich, P.R. and Daily, G.C. (2007). Persistence of forest birds in the Costa Rican agricultural countryside. Conservation Biology. 21(2): 482–494. Close ). Found in most strata of forest, including conifers, humid and wet evergreen and arid deciduous (or thorn) forest (last at least seasonally), oak and pine-oak formations, also scrub-choked narrow ravines, deep canyon bottoms where gallery forest shades moist undergrowth, grassy and bushy bracken-covered “savannas”, palm groves, coffee plantations and pastures (S Costa Rica) (6 Cohen, E.B. and Lindell, C.A. (2005). Habitat use of adult White-throated Robins during the breeding season in a mosaic landscape in Costa Rica. J. Field Orn.. 76(3): 279–286. Close ), stands of tall wild cane, riverside trees and bushy clearings; sea-level to 3000 m elevation, but rarely above 2000 m E of Isthmus of Tehuantepec; 800–1850 m in Costa Rica (but higher in Coto Brus region). In El Salvador found along edges of cloudforest, in cypress (Cupressus lusitanica) plantations, in remnant old oak forest with tangled underbrush, old coffee plantations, densely wooded ravines, thus generally in humid woodland with dense understorey. On Coiba I, Panama, occurs at sea-level in mangroves. Birds carrying radio transmitters for ten weeks in S Costa Rica had a mean home range of 0·26 km² (range 0·07–0·58 km²); each bird used a mix of habitats that included primary forest, pasture and coffee or regenerating forest (6 Cohen, E.B. and Lindell, C.A. (2005). Habitat use of adult White-throated Robins during the breeding season in a mosaic landscape in Costa Rica. J. Field Orn.. 76(3): 279–286. Close ).

Generally sedentary, but with some elevational movement between non-breeding and breeding seasons. Appears to be distributed throughout same elevation range all year, but birds at higher elevations descend lower in winter (Nov–May in parts of Sonora (Mexico), Aug–Dec in Golfo Dulce region of Costa Rica), and possibly make only seasonal use of arid deciduous forest; minor tendency to winter vagrancy, and most individuals at Coban and Vera Paz (Guatemala) disappear in Oct–Dec. In Panama, small numbers apparently disperse to both slopes of Canal area (mostly on Atlantic side) in period Oct–Apr; species almost completely disappears from Cerro Campana in dry season.

Visits fruiting trees, including figs, ripe fruit of Bumelia, in hedgerows, savannas and second growth, especially outside breeding season, generally in small flocks; seen to feed in epiphytes in tall mossy oaks, in association with Ridgwayia pinicola. Sometimes attends army ant raids (7 Vallely, A. C. (2001) Foraging at army ant swarms by fifty bird species in the highlands of Costa Rica. Ornitología Neotropical 12: 271–275. Close , 8 O’Donnell, S., Kumar, A. and Logan, C. (2010). Army ant raid attendance and bivouac-checking behavior by Neotropical montane forest birds. Wilson J. Orn.. 122(3): 503–512. Close ).

Feeds on a variety of insects, earthworms, and other invertebrates, as well as the fruits of many plant species (especially in the non-breeding season).

The vocalizations of White-throated Thrush are quite varied, especially the calls. The degree to which calls vary geographically, as well as their respective functions, has yet to be investigated.

Song of two types, one very close to that of T. migratorius, the other much louder, fuller and more melodious and with quality of mockingbird (Mimidae), but phrases again paired. The song of race daguae is apparently like that of the nominate race of T. albicollis, but slightly faster (Call a loud nasal gruff “<em>rreeuh,</em>” often doubled, a clucking “kyow” or “ch-uhk,” a rapid clucking that can become a rich yodel, “wheeljeeujeeujeeu…” (possibly same as nominate alarm call), and thick high “ssi” flight note; in Costa Rica and Panama a frog-like guttural or nasal “enk” or “nrrk,” scratchy “dzee-yoo” and, when roosting, a mellow mournful but metallic “peeyuu” or “whuueeet” or “ooeek."

Scattered data are available from across the species' range, but few studies have included data from multiple nests. Even fewer have provided ecological or behavioral data (see Causes of Mortality).

Apr–Jul in Mexico; breeding-condition birds Mar–May in Belize; Mar to early Jun in Costa Rica, to Jul in Panama.

Nest a somewhat bulky cup with layer of mud, dead leaves and twigs, fibrous lining of rootlets and outer covering of green moss, placed on the ground, a road bank, or 1–10 m up in shrub or small tree.

Clutch size 2–3, whitish, pale blue or pale greenish blue with reddish-brown and grey spots and marks.

Incubation period c. 13 days.

Nestling period c. 14 days.

In one study in S Costa Rica, nesting success varied from 4–21% depending on circumstances. Daily mortality rates were lower at well-concealed nests than at less well-concealed nests and at nests that were placed on the ground vs. in vegetation; daily mortality rates were very low at an active coffee plantation where nests were placed in heavily concealed sites (9 Lindell, C.A., O’Connor, R.S. and Cohen, E.B. (2011). Nesting success of Neotropical thrushes in coffee and pasture. Wilson J. Orn.. 123(3): 502–507. Close ).

Not globally threatened (Least Concern). Fairly common to very common in appropriate habitat in Mexico. In interior montane Belize generally abundant. In El Salvador uncommon and sparsely distributed. In Honduras locally common, primarily in forest. In Costa Rica common to abundant on Pacific face of NW divide, but population in upper Valle Central has disappeared. In Panama fairly common to common (locally and seasonally) on Pacific slope, apparently uncommon in E Darién highlands; very common (race coibensis) on Coiba I, where one of the most numerous forest birds. In Ecuador it is generally uncommon and local, but is considered one of commonest birds in lowland foothill forest around Playa de Oro (Esmeraldas).