Habitat
Subtropical and tropical high altitude grassland, shrubland. Also, subtropical and tropical montane moisr forest, heavily degraded former forest, pasturelend. From 1,850 - 3,400 m.
Subspecies
Nominate and subspecies torridus have often been considered colour morphs of a single, variable taxon. Alternatively, each has been treated as separate species; subspecies simoni has been treated either as a separate species or as a subspecies of Glow-throated Hummingbird (Selasphorus ardens). "Selasphorus underwoodii" is a hybrid between nominate subspecies and Scintillant Hummingbird (Selasphorus scintilla).
The following 3 subspecies are recognised:
simoni Carriker, 1910 - Central Costa Rica (Volcanes Poás and Barba).
flammula Salvin, 1864 - Central Costa Rica (Volcanes Irazú and Turrialba).
torridus Salvin, 1870 - Southern Costa Rica (Cordillera de Talamanca) and extreme western Panama.