The pinnated bittern is a large heron, measuring between 25–30 in (64–76 cm)[2] with a weight that ranges from 554 to 1,157 g (1.2 to 2.6 lb); males typically weigh considerably more than females.

Rectrices are black in males and brown in females; the slate-grey remiges create a conspicuous two-toned effect in flight.

[4] There are currently two recognized subspecies, which are separated by a gap in Central America:[4] The alternate name "South American bittern" is a bit misleading, as the species is found as far north as southern Mexico.

Its range stretches from the Atlantic slope of southeastern Mexico to northern Argentina, though there are few records for Guatemala and Honduras.

[6] It can be found in a variety of freshwater habitats, including dense reed beds and lake borders, flooded tall-grass pastures, marshes and overgrown ditches.

[5] The pinnated bittern is a patient hunter, often standing motionless for long periods while waiting for prey to move within range.

Its nest, a platform or shallow cup of rush stems or other plant material, is typically built among thick vegetation not far above the water surface.