
Appearance
This species is very small, a mature adult growing to only 3–3.5 in in length. The male Costa's has a mainly green back and flanks, a small black tail and wings, and patches of white below their gorgeted throat and tail. Its most distinguishing feature is its vibrant purple cap and throat with the throat feathers flaring out and back behind its head. The female Costa's hummingbird is not as distinct as the male, having grayish-green above with a white underbelly.Hybrids between this bird and the black-chinned hummingbird as well as the broad-tailed hummingbird are known.

Naming
The binomial commemorates French nobleman Louis Marie Pantaleon Costa, Marquis de Beauregard.
Reproduction
The male Costa's hummingbird's courtship display is a spirited series of swoops and arcing dives, carefully utilizing a proper angle to the sun to show off his violet plumage to impress prospective mates. Each high-speed dive will also pass within inches of the female, perched on a nearby branch, which will be accented by a high-pitched shriek.Costa's hummingbird constructs a small cup-shaped nest out of plant fibers and down and coated with lichen to hold it together. The nest will be situated above ground on a yucca stalk or tree limb. The female lays just two eggs, which are white in color, which she will incubate for 15 to 18 days before the young hatch. The young Costa's hummingbirds leave the nest after 20 to 23 days.

Food
Like all other hummingbird species, Costa's hummingbird feeds on flower nectar and any tiny insects that it happens to find in the flower petals. As with other species, it can slow down its metabolism during cold nights when it enters a hibernation-like state known as torpor and its heart and respiration rate are dramatically slowed.References:
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