Appearance

Phaethornis hermits are small to medium-sized hummingbirds with dull colored plumage. All species of Phaethornis have very long, slender bills, which in many species are slightly curved, and also have long, graduated tails in which the central pair rectrices usually are particularly elongated. Koepcke's Hermit is a relatively large Phaethornis, with a long and notably straight bill; the mandible is mostly red. The back is bronzy green, but the rump and uppertail coverts are tawny. The underparts also are mostly tawny, with a whitish throat and a tawny gray lateral throat stripe. The rectrices are dusky, and most are broadly tipped with tawny; the central pair of rectrices are greatly elongated, with very broad white tips.

The very tawny plumage and long straight bill of Koepcke's Hermit easily separate it from most of other species of Phaethornis within its range. Koepcke's Hermit is closely similar, however, to Needle-billed Hermit (Phaethornis philippii), another very tawny hermit with a long straight bill. Needle-billed Hermit is restricted to the lowlands, below ca 500 m, and so occurs a lower elevations than Koepcke's Hermit. Needle-billed Hermit also has a completely tawny throat, lacking the whitish center to the throat and the grayish tawny lateral throat stripes of Koepcke's Hermit.

Very locally, in the Mayo Valley in San Martín, Koepcke's Hermit overlaps geographically with Planalto Hermit (Phaethornis pretrei). Planalto Hermit occurs at lower elevations and in drier habitats than Koepcke's Hermit, however, and has white (not tawny) tips to the outer rectrices.

Tawny-bellied Hermit (Phaethornis syrmatophorous) of the Andes of northern Peru occurs at much higher elevations than Koepcke's Hermit, and its bill is decidedly curved.

The following description is based on Weske and Terborgh (1977):

Adult: Sexes similar. Crown blackish with a greenish gloss, the feather edged, giving a scalloped effect. Hind neck glossy greenish bronze. Back glossy bronze, becoming rufous on the rump. Uppertail coverts rufous with two or three blackish subterminal bars. Lores and auriculars blackish; short postocular streak white with rufescent tinge. Suborbital streak (from base of bill to below auriculars) buffy white. Chin and throat white, bordered on each side by a buffy gray lateral throat streak. Sides of neck grayish tan. Breast light rufescent buff centrally, darker and grayer laterally, and grading posteriorlv into rich rufescent buff on belly, flanks, and undertail coverts. Remiges and upper primary coverts glossy blackish; upper secondary coverts glossy greenish bronze. Central pair of rectrices elongate with slender, 3 mm wide tips that extend almost 2 cm beyond the tips of adjacent rectrices. Central rectrices dark glossy green basally, grading through dark grayish subterminally to white at the tips. The four lateral pairs of rectrices graduated, dark glossy green basally and black subterminally with a broad, buffy rufous tip on each vane.

Juvenile: Similar to adult, but the feathers of the upperparts are edged with dull yellow ochre, and the lateral throat streak is darker (Davis 1986).

Very little information. Probably follows the complex basic molt strategy. A specimen collected in December was molting some of the rectrices and remiges (Weske and Terborgh 1977).

Iris: dark brown

Bill: maxilla black; mandible orange red basally, distal third black

Toes: pink, flesh

Bare parts color data from Weske and Terborgh (1977) and from specimens in the Louisiana State University Museum of Natural Science.

Total length: 14–15 cm (Schulenberg et al. 2010)

Linear measurements:

male

wing length (chord), 64.6 mm (n = 1); tail length, 64.3 mm (n = 1); bill length (exposed culmen), mean 34.0 (range 33.5-34.3 mm, n = 2) (Weske and Terborgh 1977)

wing length, mean 66.88 mm ± 2.08 mm (range 63-70 mm, n = 16, series from Tarapoto region, San Martín); wing length, mean 62.93 mm ± 1.43 mm (range 61-77 mm, n = 22, series from all other localities); bill length, mean 37.44 mm ± 1.14 mm (range 33-39.5 mm, n = 39) (Hinkelmann 1988)

female

wing length (chord), mean 58.3 mm (range 57.0-60.1 mm, n =6); tail length, mean 61.4 mm (range 60.0-62.5 mm, n = 6); bill length (exposed culmen), mean 31.8 (range 29.5-32.6 mm, n = 6) (Weske and Terborgh 1977)

wing length, mean 62.56 mm ± 1.01 mm (range 61-64 mm, n = 9, series from Tarapoto region, San Martín); wing length, mean 57.57 mm ± 1.29 mm (range 63-70 mm, n = 23, series from all other localities); bill length, mean 34.48 mm ± 0.83 mm (range 33-36 mm, n = 32) (Hinkelmann 1988)

Mass: male, mean 5.4 g (range 4.7-5.8 g, n = 14); female, mean 4.7 g (range 4.5-4.9 g, n = 9) (Davis 1986)