About Nyctibius griseus (J.F.Gmelin, 1789)
Common potoos, scientifically named Nyctibius griseus, are 34–38 cm (13–15 in) long, with mottled red-brown, white, black, and grey cryptic plumage. This disruptive coloration lets them camouflage against tree branches. Males and females look very similar, and cannot be told apart through visual observation. Their eyes can either look like large black dots with a small yellow ring, or large yellow irises with small pupils, because the bird can voluntarily constrict its pupils. The common potoo has two or three slits in its eyelid that stay open at all times, letting it see even when its eyelids are closed. Its upper and lower eyelids can move independently and rotate over the eye to the desired position, so the bird can adjust its field of vision. It has an unusually wide mouth, with a tooth on the upper mandible that is used for foraging. Its song is haunting and melancholic: a repeating BO-OU, BO-ou, bo-ou sequence that gradually drops in both pitch and volume. When seized, the bird produces a squeaky sound similar to that of a crow. This call is very different from the much deeper, more dramatic call of the northern potoo. The nominate subspecies of the common potoo is found in Trinidad and Tobago and every mainland South American country except Chile, though it has been recorded as a vagrant in Chile. In its South American range, it occurs from the Andes to the Atlantic Ocean. The subspecies N. g. panamensis ranges from eastern Nicaragua south through Costa Rica and Panama, and west of the Andes from northwestern Venezuela through Colombia and Ecuador into northwestern Peru. The common potoo is a resident breeder that lives in open woodlands and savannah. It avoids cooler montane regions, and is rarely seen above 1,900 m (6,200 ft) above mean sea level even in the warmest parts of its range. It generally avoids arid regions, but was recorded in the dry Caribbean plain of Colombia in April 1999. It has many populations living in gallery forest-type environments around the border between Uruguay and Brazil. A bit further south, where the ratio of woodland to grassland is somewhat lower, it is decidedly rare. Further due west, in Argentina's Entre RÃos Province which has abundant riparian forest, it is also not common. Birds at the southern end of the common potoo's range may migrate short distances northward during winter.
