About Zebrilus undulatus (Gmelin, 1789)
Adults of Zebrilus undulatus have gray plumage marked with fine zigzag barring, a pale underside, and reach a standing height of around 32 centimeters (12 and a half inches). Juveniles have a dark back, with a brown head and brown underside. Because of its appearance, this species was often grouped with tiger herons in the genus Tigrisoma and their close relatives. However, it is actually a true bittern. Like other bitterns, it only has 10 rectrices, while other Ardeidae have 12. DNA sequence data also confirms it definitely belongs to the bittern lineage. Its short legs, short necks, and cryptic plumage may therefore be plesiomorphic traits across the heron family Ardeidae as a whole. The zigzag heron, the common name for this species, occurs across the entire Amazon Basin located east of the Andes cordillera, and is found in the five countries bordering the basin's western periphery: Colombia, Venezuela, Ecuador, Peru, and Bolivia. To the northwest, its range does not extend beyond the Orinoco River basin in Venezuela. To the east-northeast, its range includes the Guianas. In the southeastern Amazon Basin, its range does not extend east of the Tapajós River drainage.
