The Calliope hummingbird is the smallest breeding bird found in Canada and the United States. Adults are glossy green on the back and crown with white underparts. Males have wine-red streaks on the gorget, green flanks and a dark tail. Females and immatures have a pinkish wash on the flanks, dark streaks on the throat and a dark tail with white tips.
Calliope hummingbirds breed in western North America from southern British Columbia and Alberta south to Colorado and southern California. During spring and summer, they move, mainly through Arizona and New Mexico and northern Mexico, to winter in southwestern Mexico as well as in Guatemala and Belize. The breeding habitat of Calliope hummingbird is varied among open shrub habitats and altitudes. Open montane forest, mountain meadows, and willow and alder thickets may variously serve as breeding grounds. During migration and winter, these birds occur in chaparral, lowland brushy areas, deserts, and semi-desert regions.
Calliope hummingbirds are solitary and interact with each other only during the breeding season. They are territorial and males aggressively defend their breeding and feeding territories from intruders. Calliope hummingbirds are active during the day; they spend their time perching or hovering above flowers in search of nectar which they extract using a long extendable tongue. They may also catch small insects on the wing. Calliope hummingbirds are migratory birds and generally leave their breeding grounds earlier than most birds to take advantage of the late-summer wildflowers in the mountains of western North America.
Calliope hummingbirds are polygynous and don't form pairs. Adult males usually arrive on the breeding ground before females, from mid-April to early May. The male claims and vigorously defends a nesting territory in which he will breed with many females. During courtship, a male hovers, creating a loud buzzing sound, with throat feathers protruding and facing a female. The male then ascends temporarily to 20 meters and dives at high speed, with the rapid descent causing sonation of the wing and tail feathers combined with vocalization, intending to attract the attention of the female. The male takes no part in raising the young and often leaves the breeding grounds by the time the young hatch. The female builds an open cup nest alone usually in a conifer tree under an overhanging branch. She lays 2 eggs from late May to early July and incubates them for 15 to 16 days. The chicks hatch naked and helpless. They are capable of flight about 20 days after hatching and reach reproductive maturity at around one year of age.
Little information is available on the overall issues that are causing declines in Calliope hummingbird populations; however, possible threats include habitat loss, increased use of pesticides, and replacement of native plants by non-native plants. The restricted wintering range of Calliope hummingbirds makes the species more susceptible to natural disasters, diseases, or land use changes that could wipe out significant portions of the population.
According to the What Bird resource, the total population size of the Calliope hummingbird is around 1 million individuals. According to the All About Birds resource, the total breeding population size of the species is around 4.5 million birds. Overall, currently, Calliope hummingbirds are classified as Least Concern (LC) on the IUCN Red List and their numbers today are stable.
Calliope hummingbirds play a very important role in their local ecosystem. While collecting nectar, they transfer the pollen and assist in plant pollination.