The Tooth-billed Hummingbird is endemic to the humid lowland and foothills of the Choco, from northwestern Ecuador to southeastern Panama. Though hummingbird bills, in general, are very diverse in size and shape, few are structurally modified in other ways. The Tooth-billed Hummingbird derives its name from its straight bill that has a prominent hooked tip and backward-pointing tooth-like serrations on the distal half. This modification is absent on the female bill, and thus may be related to sexual selection. More plausible, though not necessarily mutually exclusive, is that this distinctive bill morphology, found in 27 other hummingbird genera, is an adaptation for nectar robbing of flowers with inaccessible nectar, an adaptation convergent with Flowerpiercers (Diglossa).