Wood-rails (Aramides) are large rails with stout, long, yellow green bills; black rear parts (lower flanks, undertail coverts, rump, and tail); rufous or reddish brown primaries; and stout, red tarsi and toes. The rufous head, neck, and breast for which Rufous-necked Wood-Rail is named are its most defining characteristic. There is a gray patch at the base of the neck, on the nape; the back is olive green. As in other wood-rails, the rump, tail, and lower belly are dusky to black. The irides range from orange to brown, the bill is greenish fading to yellow at the base, and the legs are coral red. The sexes of the adults are similar; juveniles are duller and appear more gray which can lead to confusion with similar species.
Rufous-necked Wood-Rail overlaps geographically with four similar species: Little Wood-Rail (Aramides mangle), Gray-necked Wood-Rail (Aramides cajaneus), Brown Wood-Rail (Aramides wolfi), and Uniform Crake (Amaurolimnas concolor) (Restall et al. 2007). Little Wood-Rail is slightly smaller than Rufous-necked, and has a gray (not rufous) crown and neck. There also is very little contact between these two species; Little Wood-Rail essentially is endemic to Brazil, with only a single record from French Guiana, where it is assumed to be only a vagrant. Gray-necked Wood-Rail is larger than Rufous-necked, and has an entirely gray head and neck; also, Gray-necked has a paler, cinnamon rufous belly. Brown Wood-Rail is larger than Rufous-necked, with a gray head, and the body plumage is dark and duller brown. Uniform Crake is much smaller than the wood-rail, with shorter bill and tarsi, and uniform rufous brown plumage, not as bright rufous as the foreparts of Red-necked Wood-Rail, and lacking the black rear parts of the wood-rail.
The following description is based on Wetmore (1965) and on Taylor (1998):
Adult: Sexes similar. Head, neck and breast rufous brown. Nape and extreme upper back gray. Back and scapulars olive brown or greenish olive. Primary coverts greenish olive, washed with cinnamon rufous basally. Primaries chestnut or cinnamon rufous; secondaries more greenish olive. Rump, tail, flanks, and undertail coverts black. Throat white. Belly grayish brown. Underwing coverts white, barred with black.
Juvenile: Much duller. Forecrown to nape buffy brown to grayish brown, tinged with cinnamon. Upperparts otherwise as in adult, but paler and duller. Sides of head, and chin to upper neck, pale buffy brown to dirty white, strongly washed with vinaceous cinnamon. Rest of underparts buffy brown, washed with ochre cinnamon. Lower flanks to undertail coverts deep brownish olive.
Iris: orange brown
Bill: greenish yellow, darker towards the tip
Tarsi and toes: dull red
Bare parts color data from Wetmore (1965).
Total length: 29-31.5 cm (Howell and Webb 1995, Ridgely and Greenfield 2001b), 33 cm (Hilty 2003)
Linear measurements (from Ridgway and Friedmann 1941):
male (n = 18)
wing length: mean 169 mm (range 163-174 mm)
tail length: mean 58.3 mm (range 53-63.0 mm)
bill length (exposed culmen): mean 43.7 mm (range 39.5-46 mm)
tarsus length: mean 59.5 mm (range 52.5-63 mm)
female (n = 13)
wing length: mean 163.6 mm (range 145.5-170 mm)
tail length: mean 57.3 mm (range 47-62.5 mm)
bill length (exposed culmen): mean 42.2 mm (range 37.5-46 mm)
tarsus length: mean 57.6 mm (range 50-60.5 mm)
Mass: male, 302 g, 327 g (n = 2; Haverschmidt 1968)