An adult male is marked by a black facial mask extending from the forehead toward the sides of the neck and by bright yellow underparts. In Costa Rica, the bird uses wet grassy places and marsh cover and is usually in pairs.
In the adult male, the black mask reaches from the front of the crown to the sides of the neck. It meets the olive upperparts without a grey or white border; the underparts are bright yellow, with stronger olive on the sides.
In Costa Rica, it uses wet pastures, marshes with tall vegetation and tall grass beside rivers or ponds, usually in pairs.
In Costa Rica, it builds a cup nest of grass stems and leaves, lined with finer grass, 25–75 cm above ground in a large, dense grass tuft.
In Costa Rica, females lack the black facial mask and have a short yellow stripe from the bill to above the eye. The lores and cheeks are olive, and olive covers more of the flanks than in males.
Juveniles in Costa Rica are browner and more olive above, with paler, duller yellow underparts and a buff wash on the upper throat and breast.
An extinction-risk assessment has not been added yet.