The Buff-bellied Hummingbird is notable for its red bill and throat that can look blue-green in the right light. It feeds in South Texas, and some birds move to Louisiana for winter.
Its belly is warm buff and its bill is brilliant red. In the right light, the throat and breast can appear blue-green.
Young male Buff-bellied Hummingbirds can show a red-and-black upper bill while male coloration is still developing. In first-cycle plumage, their wing coverts are duller green than the bright metallic basic feathers. Juvenile tail feathers are narrow with dusky bronze-green tips; basic tail feathers are broader and more clearly edged. The Belize analysis included N=59, with 18 first-cycle samples.
The preformative molt replaced 0–3 inner greater coverts (mean 0.2). Male bill color matured later, and most first-cycle formative males showed mixed red and black on the upper mandible. Bill corrugations reached 0% by definitive-cycle basic plumage. Most definitive prebasic molt occurred in March–May, while the second prebasic molt peaked in June–September.
An extinction-risk assessment has not been added yet.