The Double-striped Thick-knee easily is overlooked during the day, when it crouches in the grass, which its brown-and-gray streaked plumage matches well. It is more easily spotted at night, when it calls noisily and may be located by the strong reddish reflections of its eyes when illuminated (Land 1970, Garrigues 2007). Shaped somewhat like a long-legged plover, with somewhat thickened “knees” (actually the ankles), the broad white superciliary and short, stout bill set the thick-knee apart from any shorebird (Garrigues 2007).
Similar to the Peruvian Thick-kee (Burhinus superciliaris), but the Double-striped Thick-knee is larger, darker and more heavily patterned above, with a heavier bill and darker crown, and a more distinct contrast between the dark breast and the white belly. In flight it shows a less contrasting wing pattern (Hume 2004). There also is no geographic overlap between these two species.
Although somewhat similar to plovers and other shorebirds, the thick-knee can be distinguished from these by its broad white superciliary and short, stout bill (Garrigues 2007).
The following description is based on Blake (1977), and refers to nominate bistriatus (see also Ridgway 1919); see Geographic Variation for the distinguishing characters of the other subspecies:
Adult: Sexes similar. Sides of crown, or entire crown, black. A prominent white superciliary. Upperparts dark brown, striped fulvous. Remiges mostly fuscous brown; the primaries are extensively white at the base or on the inner webs. Rectrices tipped black; lateral rectrices also barred white and fuscous brown. Center of throat white. Malar area and sides of the neck tawny, with narrow dark brown streaks. Foreneck and breast paler, often grayish, and with dark shaft streaks. Abdomen white, rather sharply set off against the brown or grayish of the breast. Undertail coverts uniform cinnamon.
Juvenile: Similar to the adult, but more rufescent above, and somewhat mottled.
Soft part colors are from Ridgway (1919) and Blake (1977):
Bill: mostly black, base of mandible gray or greenish.
Tarsi and toes: greenish yellow or yellow.
Burhinus bistriatus - total length 43-51 cm (Land 1970, Sick 1993, Garrigues 2007). Mass 700 g (male; n=?; Sick 1993), 787 g (n=1, Oaxaca, Mexico; Dunning 2008).
Burhinus bistriatus pediacus (Wetmore and Borrero 1964):
males (n=6): wing (flat) 240-253 mm (mean 245 mm); tail 115.5-124.3 mm (mean 117.8 mm); culmen from base 47.3-49.4 (mean 48.6 mm); tarsus 101.5-115.0 mm (mean 108.5 mm)
females (n=3), wing (flat) 242-249 mm (mean 244 mm); tail 115.6-122.5 mm (mean 119.6 mm); culmen from base 46.9-53.1 mm (mean 49.8 mm); tarsus 101.0-111.8 mm (mean 107.5 mm)