[6] The white-bellied mountaingem forages for nectar in flowering trees and shrubs, and is especially partial to epiphytes of family Ericaceae and genus Columnea.

In addition to nectar, it also feeds on insects captured by hawking; females sometimes glean arthropods from foliage.

The white-bellied mountaingem's song is "a medley of squeaks, dry or liquid trills, and sputtering notes."

"[6] The IUCN has assessed the white-bellied mountaingem as being of Least Concern, though it has a somewhat restricted range and its population size and trend are not known.

[1] It is considered locally common and much of its habitat remains intact, especially in three Costa Rican national parks.