Appearance

Tinamous are stocky terrestrial birds with rounded wings and very short tails. Nothuras are five species of small, short billed, tawny tinamous, all of which inhabit grasslands or open scrub. Darwin’s Nothura is a small tawny tinamou with a rather short-necked appearance. The upperparts are tawny, the feathers with central black bars and narrow light gray margins. The head and neck are tawny, dotted with dusky. The underparts are primarily tawny, the neck and breast more or less streaked with dusky. The sexes are similar.

Throughout most of its geographic range, Darwin's Nothura is distinguished by its open habitat and small size: it is much smaller and tawnier than Ornate Tinamou (Nothoprocta ornata), and smaller than Andean Tinamou (Nothoprocta pentlandii) with a much shorter bill and a more strongly marked breast. Andean Tinamou also occurs at lower elevations, and is not likely to be syntopic with this nothura. Darwin's Nothura is similar to the four other species of nothura, of which there is geographic overlap only with Spotted Nothura (Nothura maculosa). These two species are very similar to one another, but Spotted Nothura has longer tarsi and toes (e.g., middle toe with claw typically 24-28 mm in Darwin's but over 28 in most subspecies of Spotted; Conover 1950). The inner webs of the outermost primaries of Spotted are barred, whereas these inner webs usually are unbarred in Darwin's. The two nothura also have different vocalizations.

The following description is based on Bump and Bump (1969) and Blake (1977) and refers to nominate darwinii; see also Geographic Variation:

Adult: Sexes similar. Crown rufescent brown, barred with brownish black, and with some whitish streaks. Upperparts generally dark brown, the feathers with narrow transverse bands of light brown and rufous, and with narrow whitish streaks. Wing coverts and secondaries (both webs) barred reddish buff and brown; primaries similar, but the pale markings on the inner webs are restricted to the bases of the feathers, and are reduced or absent towards the tips. Throat white, sometimes with darker spots. Supercilium and sides of head buff, sprinkled with darker spots. Neck and breast rufescent brown, the feathers barred with black, producing a streaked or somewhat spotted pattern. Belly and flanks tawny buff, flanks with narrow brown bars.

Immature: Similar to adult, but throat paler, sometimes pure white. Breast spotted (not streaked) with black.

Little information.

Iris: light yellow or dusky lemon yellow (male); apricot orange, yellow orange or orange brown (female)

Bill: maxilla dusky brown; mandible whitish brown or yellowish

Tarsus and toes: pale yellow, pale gray brown, vinaceous buff

Bare parts color data from Wetmore (1926), Bump and Bump (1969), Blake (1977), and specimens in the Louisiana State University Museum of Natural Science.

Iris color varies with age. At hatching, the irides are medium to dark brown. By the age of one and a half weeks, the irides become paler and grayer, and by the third week the irides are deep blue. Within five weeks, the color changes from blue to blue green, although the irides of some individuals have become dusky yellow. At six weeks, most birds have dusky yellow irides, although often with a greenish cast. By eight weeks, the iris is dusky lemon yellow in males and medium dark yellow in females, sometimes with suggestion of rufous. At ten to twelve weeks most males have dusky lemon yellow irides, as in adults, although still not as dark as the irides will become at one to two years old. The irides of females change to a much darker yellow bordering on rufous; with age, the females lose all yellow in the iris and the iris becomes a rich deep orange brown (Bump and Bump 1969).

Total length: 25-27 cm (Blake 1977), 26 cm (Fjeldså and Krabbe 1990)

Linear measurements (from Blake):

peruviana, male (n = 1)

wing length (flat): 126.5 mm

peruviana, female (n = 3)

wing length (flat): range 130-133 mm

bill length: range 18-20 mm

agassizii, male (n = 6)

wing length (flat): mean 138.5 mm (range 133-143 mm)

bill length (exposed culmen): mean 17 mm (range 16-18 mm)

agassizii, female (n = 6)

wing length (flat): mean 143 mm (range 133-151 mm)

bill length (exposed culmen): mean 18.3 mm (range 16-20 mm)

boliviana, male (n = 7)

wing length (flat): mean 135.5 mm (range 130-142 mm)

bill length (exposed culmen): mean 17.5 mm (range 17-19 mm)

boliviana, female (n = 5)

wing length (flat): mean 135.8 mm (range 130-141 mm)

bill length (exposed culmen): mean 17.2 mm (range 16-18 mm)

salvadorii, male (n = 6)

wing length (flat): mean 147.3 mm (range 131-154 mm)

bill length (exposed culmen): mean 18 mm (range 17-19 mm)

salvadorii, female (n = 5)

wing length (flat): mean 145.6 mm (range 132-153 mm)

bill length (exposed culmen): mean 18.4 mm (range 17-20 mm)

darwinii, male (n = 7)

wing length (flat): mean 132.7 mm (range 128-136 mm)

bill length (exposed culmen): mean 18 mm (range 17-19 mm)

darwinii, female (n = 4)

wing length (flat): mean 139 mm (range 134-146 mm)

bill length (exposed culmen): mean 18.2 mm (range 18-19 mm)

Mass:

darwinii, male, mean, 214 g (range 200-245 g, n = 13; Bump and Bump 1969: 150)

darwinii, female, mean, 243 g (range 209-285 g, n = 16; Bump and Bump 1969: 150)

salvadorii, male, mean, 250 g (range 192-250 g, n = 27; Bump and Bump 1969: 151-152)

salvadorii, female, mean, 274 g (range 197-330 g, n = 27; Bump and Bump 1969: 151-152)