SPECIES

Long-billed Gnatwren Ramphocaenus melanurus

Harold F. Greeney, Jonathan L. Atwood, Susannah Lerman, and Andrew J. Spencer
Version: 2.0 — Published July 16, 2020

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Identification

10.5–13.5 cm. Long-billed Gnatwren is a slender, wren-like bird with a very long, straight, slender bill and a long, slender tail that often is held cocked upwards or waved about in a characteristic manner (see Behavior). The nominate subspecies (of eastern Brazil) has pale lores, a buffy eyestripe and dark auriculars that contrast with the paler cheeks. It also has a broken, whitish eyering and a whitish throat with dark spots. Above it is uniform tawny brown, and below largely buffy, with a tinge of cinnamon on the sides. The long, graduated tail is blackish, with small white tips on the outer rectrices.

Similar Species

The Long-billed Gnatwren is not likely to be confused in most of its range, being easily recognized by its extremely long, straight bill, long blackish tail, and distinctive tail wagging habits (see Behavior). Collared Gnatwren (Microbates collaris) and Tawny-faced Gnatwren (Microbates cinereiventris) have stubbier tails, shorter bills, and decidedly different plumage patterns (2, 3, 4). Locally in southwestern Amazonia, Long-billed Gnatwren is syntopic with the very similar Chattering Gnatwren (Ramphocaenus sticturus); Chattering Gnatwren formerly was included within Long-billed, but now is recognized as a separate species (see Systematics History). The two are most readily distinguished by song, which in Chattering Gnatwren is not a trill, but instead is a repeated series of two or three elements, such as a string of ticking notes followed by a series of churt notes, etc. Plumage is very similar between the two species, but Chattering is distinguishable by broad white tips on the outer rectrices. The two also differ; in this region of Amazonia, Long-billed is restricted to humid evergreen forest, whereas Chattering apparently is confined to bamboo dominated forests, or, locally, to seasonally deciduous forest.

Plumages

The following pertains to the the rufiventris subspecies, unless otherwise noted:

Natal Down

No published information, but see ML113762251 (also below).

Juvenile (First Basic) Plumage

Described as duller than Adult Plumage, potentially with darker mottling on the face, particularly on cheeks. The only two descriptive accounts of the immature plumage are all in reference to the Central American rufiventris. Unfortunately, neither description provides a clear indication as to the age of the birds described. The immature plumage is described by Ridgway (5) as “Essentially like adults, but back, rump, etc., soft grayish brown (nearly concolor with pileum and hindneck), and under parts pale grayish brown, approaching dull buffy whitish on throat and abdomen.” Stiles and Skutch (6) provide a similar description: “pileum and nape buffy brown; rest of upperparts dull brown, with much less contrast than in adult; face duller, more tawny; throat buff, smudged with dusky and white; breast grayish-brown, fading to whitish on belly; wings with olive-brown edgings.” From only a quick glimpse of a fledgling on the day it left the nest, Skutch (7) noted that the plumage of the upperparts was almost concolorous gray brown; the head and hindneck, being only slightly browner than the more posterior upper parts.

Formative Plumage

No information.

Definitive Basic Plumage

Head, breast, and flanks are tawny cinnamon. The crown and nape are a dull chocolate brown, becoming grayer brown on the scapulars, back, and rump. The face is uniformly cinnamon/tawny with an indistinct dusky eyestripe, and thin buffy eyering. The throat is white, with indistinct streaks. The center of the belly and undertail coverts are whitish. The tail is blackish with all but the central rectrices tipped white; the tips of the outermost rectrices being most extensive. The wings have a slightly more olive-brown cast than the upperparts; the coverts with darker centers.

Molts

Little information, but molt follows the Complex Basic Strategy (8). The Preformative Molt is incomplete, apparently molting the body feathers and perhaps the wing coverts, but retaining the juvenile remiges and remiges (9, 8). Definitive Prebasic Molt is complete (8).

Bare Parts

Bill

Maxilla black, mandible pale gray (amazonum, 10); maxilla horn brown, sometimes darker near tip, mandible pale blue gray to pinkish gray (rufiventris, 5); pinkish gray, darker on culmen (rufiventris, 11; mostly brownish, paler, pinkish white along tomia, white to bluish white at base of mandible (trinitatis, Herklots 1961); maxilla brown, mandible grayish white, edged with pale brown (pallidus; 12); maxilla brown, mandible grayish tan (duidae, 13); maxilla slightly reddish brown, mandible paler, pale brownish pink along the lower margin (badius, dried skin; 14).

Mouth Lining

Linings of maxilla and mandible violet gray, tongue and inside of mouth pink (rufiventris; 15).

Iris and Facial Skin

Iris is brown (amazonum, 10; rufiventris, 5); pale brown (rufiventris, 16; pallidus, 12); medium brown (duidae, 13).

Tarsi and Toes

Bluish gray (amazonum, 10; rufiventris, 5); pale plumbeous (trinitatis, 17); plumbeous (pallidus; 12); gray (duidae, 13; rufiventris, 11); dull slate (duidae, dried skin; 14); dark gray (rufiventris, 16); tarsi and toes slate gray, claws pinkish gray, undersides of toes pale green (rufiventris, 15)

Measurements

Linear Measurements

Ramphocaenus melanurus rufiventris (♂♂)

Total length (skins) – 10.9-12.7, mean 12.0 cm (n = 18; 5); 10.5-11.8 cm (n = ?; 16)

Wing – 46-54.5, mean 51.2 mm (n = 18; 5); 47.5-54.0, mean 50.0 mm (n = 10; 16)

Tail – 36.5-43.5, mean 40.9 mm (n = 18; 5); 37.4-48.2, mean 41.7 mm (n = 10; 16)

Culmen – 22-26, mean 24 mm (n = 18; 5); 22.7-25.7, mean 23.9 mm (n = 10; 16)

Tarsus – 20-21.5, mean 20.9 mm (n = 18; 5); 19.3-21.1, mean 20.1 mm (n = 10; 16)

Middle Toe – 10.5-12.0, mean 11.1 mm (n = 18; 5)

Ramphocaenus melanurus rufiventris (♀♀)

Total length (skins) – 10.5-11.9, mean 11.3 cm (n = 16; 5)

Wing – 45.5-53, mean 49.2 mm (n = 16; 5); 46.6-51.5, mean 48.5 mm (n = 10; 16)

Tail – 36-41, mean 38.6 mm (n = 16; 5); 33.5-39.0, mean 37.3 mm (n = 10; 16)

Culmen – 20-24.5, mean 23.1 mm (n = 16; 5); 21.6-24.8, mean 23.5 mm (n = 10; 16)

Tarsus – 20-22, mean 21.3 mm (n = 16; 5); 19.7-21.8, mean 20.7 mm (n = 10; 16)

Middle Toe – 11-11.5, mean 11.2 mm (n = 16; 5)

Ramphocaenus melanurus rufiventris (sexes combined)

Total length – 10.5-11.8 cm (n = ?; 16)

Ramphocaenus melanurus ardeleo (♂♂)

Wing – 52, 50, 52, 52.5, 54.5 mm (18)

Tail – 44, 41, 46 mm (18)

Ramphocaenus melanurus ardeleo (♀♀)

Wing – 50, 50 mm (18)

Tail – 40 mm (18)

Ramphocaenus melanurus sanctaemartae (♀♀)

Wing – 47 mm (5)

Tail – 38 mm (5)

Culmen – 24.5 mm (5)

Tarsus – 22 mm (5)

Middle Toe – 12 mm (5)

Ramphocaenus melanurus sanctaemartae (♂♂)

Wing – mean 51.6 mm (n = 4; 5)

Tail – mean 44.5 mm (n = 4; 5)

Culmen – mean 25.1 mm (n = 4; 5)

Tarsus – mean 21.9 mm (n = 4; 5)

Middle Toe – mean 11.4 mm (n = 4; 5)

Ramphocaenus melanurus griseodorsalis (♀♀)

Wing – 48 mm (holotype; 19)

Tail – 43 mm (holotype; 19)

Culmen – 21 mm (holotype; 19)

Tarsus – 20 mm (holotype; 19)

Ramphocaenus melanurus pallidus(♀♀)

Wing – 47 mm (12)

Tail – 44 mm (12)

Bill – 21.5 mm (12)

Ramphocaenus melanurus trinitatis (♂♂)

Wing – 50, 50, 49 mm (20)

Tail – 42, 45, 49 mm (20)

Culmen – 20, 20, 19 mm (20)

Tarsus – 20, 21, 19 mm (20)

Ramphocaenus melanurus trinitatis (♀♀)

Wing – 48 mm (20)

Tail – 39 mm (20)

Culmen – 19 mm (20)

Tarsus – 21 mm (20)

Ramphocaenus melanurus trinitatis (sex unknown)

Wing – 48, 51 mm (20); range 48-54 mm (n = ?, 21)

Tail – 45, 42 mm (20); range 43-48 mm (n = ?, 21)

Bill – 20, 18 mm (culmen; 20); 21-23 mm. (n = ?, 21)

Tarsus – 20, 19 mm (20)

Ramphocaenus melanurus badius (♂♂)

Wing – 53 mm (holotype; 14); 53, 53, 49 mm (10)

Tail – 42 mm (holotype; 14); 49, 52.5, 47 mm (10)

Culmen (exposed) – 22 mm (holotype; 14); range 23-24 mm (n = 3; 10)

Culmen (from base) – 26.5 mm (holotype; 14)

Tarsus – 20 mm (holotype; 14)

Ramphocaenus melanurus badius (♀♀)

Wing – 49 mm (14)

Tail – 41.5 mm (14)

Culmen (exposed) – 20 mm (14)

Culmen (from base) – 24.5 mm (14)

Tarsus – 19.5 mm (14)

Ramphocaenus melanurus albiventris (♂♂)

Total length – 11.7 mm (22)

Wing – 47 mm (22)

Tail – 43 mm (22)

Culmen (exposed) – 22 mm (22)

Tarsus – 20 mm (22)

Ramphocaenus melanurus albiventris (♀♀)

Wing – 42 mm (22)

Ramphocaenus melanurus amazonum (♂♂)

Wing – 54.5, 54 mm (21); 52 mm (14); 51-55 mm (n = ?, 23)

Tail – 50, 49 mm (21); 53 mm (10); 53 mm (10); 46.5-50.5, mean 48.1 mm (n = ?, 24); 50-53 mm (n = ?, 23)

Bill – 22, 25 mm (21); 23 mm (10); 20-23 mm (culmen; n = ?, 23)

Tarsus – 18-21 mm (n = ?, 23)

Ramphocaenus melanurus amazonum (♀♀)

Wing – 51 mm (21); 51-53 mm (n = ?, 23)

Tail – 49 mm (21); 44-48.5, mean 46.2 (n = ?, 24); 47-51 mm (n = ?, 23)

Bill – 21-23 mm (culmen, n = ?, 23)

Tarsus – 19-20 mm (n = ?, 23)

Ramphocaenus melanurus austerus (♂♂)

Wing – 50.5 mm (holotype; 14)

Tail – 45.5 mm (holotype; 14)

Culmen (exposed) – 20 mm (holotype; 14)

Culmen (from base) – 23.25 mm (holotype; 14)

Tarsus – 20.5 mm (holotype; 14)

Ramphocaenus melanurus duidae (♂♂)

Wing – 48 mm (holotype; 14)

Tail – 44.75 mm (holotype; 14)

Culmen (exposed) – 21 mm (holotype; 14)

Culmen (from base) – 24 mm (holotype; 14)

Tarsus – 19.5 mm (holotype; 14)

Ramphocaenus melanurus melanurus (♂♂)

Wing – 53 mm (25)

Tail – 53 mm (25)

Culmen – 21 mm (25)

Ramphocaenus melanurus melanurus (sex unknown)

Wing – range 46-52 mm (n = ?, 21)

Tail – range 44-49 mm (n = ?, 21)

Bill – range 21-22.5 mm (n = ?, 21)

MASS

Ramphocaenus melanurus rufiventris

♂♂ – 8.6, 8.6, 8.8, 9.0, 9.1, 10.1, 10.1, 10.2, 10.5, 10.6 g (26)

♀♀ – 8.6, 9.0, 11.0 g (26)

sex unknown – 9.0 g, 11.0 g (15); mean 11 g, 10 g (n = ?, Costa Rica and Panama, respectively; 27); 9.7 ± 0.9 g (n = 17; 28).

Ramphocaenus melanurus ardeleo

♂♂ – 9.0, 9.1, 9.6 g (29); 8.2, 7.4 g (18)

♀♀ – 9.8 g (30); 8.1-9.6, mean 8.78 ± 0.69 g (n = 5; 29); 8.3, 8.1 g (18)

Ramphocaenus melanurus trinitatis

♂♂ – 6, 6, 7.5 g (20)

sex unknown – 8.5 g (20); range 8.5-9.5, mean 9.2 g (n = 9; 31); 8 g (32)

♀♀ – 8 g (31); 8 g (20)

Ramphocaenus melanurus pallidus

Sex unknown – 8 g (33); mean 7.5 g (n = 6; 34)

Ramphocaenus melanurus amazonum

♂♂ – 10.8 g, 9.2 g, 10.3 g (35)

Ramphocaenus melanurus griseodorsalis

♂♂ – 10.2 g, 9.6 g (36)

♀♀ – 10.7 g (36)

Ramphocaenus melanurus albiventris

♂♂ – 8.2, 8.7 g (37)

♀♀ – 8.3 g (37)

Mean 9 g (n = ?, sex unspecified, Manaus, Brazil; 27).

Ramphocaenus melanurus duidae

sex unknown – 9.8 g, 10.0 g (38)

Recommended Citation

Greeney, H. F., J. L. Atwood, S. Lerman, and A. J. Spencer (2020). Long-billed Gnatwren (Ramphocaenus melanurus), version 2.0. In Birds of the World (T. S. Schulenberg, B. K. Keeney, and S. M. Billerman, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.lobgna5.02