Large, stout woodcreeper of tall rainforest. Plumage entirely rufous-brown with no barring or streaking; note thick red bill and prominent whitish malar mark (bill of young birds is dark brown). Found in tall rainforest as well as slightly lower-stature forests on sandy soils; generally less common than other large woodcreepers. Climbs along tree trunks and large branches at middle and upper levels, probing bark crevices for insects and small vertebrates; occasionally follows army ant swarms to capture animals fleeing up tree trunks. Heard more often than seen. Song, given mainly at dawn, is a far-carrying, hoarse screech repeated 3–4 times, very unlike other woodcreepers. Amazonian Barred-Woodcreeper, which also has a reddish bill and suggestion of a pale whisker, may occur with Red-billed at ant swarms and be mistaken for it in dim understory light; note Red-billed’s stouter bill and plain face with obvious whisker streak.