[9] The proposed phylogenetic system for hummingbirds suggested by McGuire et al. (2009)[10] accommodated the possible elevation of these subspecies to species rank.

Giant hummingbirds can be identified by their large size and characteristics such as the presence of an eye-ring, straight bill longer than the head, dull colouration, very long wings (approaching the tail tip when stowed), long and moderately forked tail,[11] tarsi feathered to the toes and large, sturdy feet.

[19] Hummingbirds are extremely agile and acrobatic flyers, regularly partaking in sustained hovering flight, often used not only to feed on the wing but to protect their territory[20] and court mates.

[23] It regularly feeds from the flowers of the genus Puya in Chile, with which it has a symbiotic relationship, trading pollination for food.

[20][25][26] Considering the energy-rich nature of nectar as a food source, it attracts a large range of visitors apart from the hummingbird, which has coevolved with a plant to be the flower's most efficient pollinator.

[24] If alien species are introduced that become nectar thieves, it is reasonable to predict that their activities will significantly impact the local ecosystem.

This could prove to be a future risk for the giant hummingbird populations because they sit close to the physical limit in their metabolic demands.

[28] A giant hummingbird nest is small considering the size of the bird, typically made near water sources and perched on a branch of a tree or shrub parallel to the ground.