The Calliope Hummingbird is the smallest North American breeding bird. Defending its territory with a body mass about half that of North America's smallest passerine, the Bushtit (Psaltriparus minimus), or a third that of the smallest wood- warblers (Parulinae), the Calliope Hummingbird lives up to its heroic specific name, that of the muse of epic poetry. Stellula means “little star,” a name especially suited to the male Calliope Hummingbird when he flashes the magenta rays of his beautiful and unique gorget.
The Calliope Hummingbird survives and breeds successfully in chilling northwestern montane environments, despite having the severe thermal disadvantage of a high ratio of surface exposure to heat-producing tissue mass. Flight speed, endurance on fuel reserves, and brain size (storage capacity) are some of the size-dependent characteristics that can limit migratory travel, so the Calliope Hummingbird is of special interest as the smallest long-distance avian migrant in the world. Seasonal distribution records tell us that some Calliope Hummingbirds must travel 9,000 km annually. Recent winter records in the southeastern United States suggest potential range extensions in this species, perhaps associated with environmental changes caused by humans.
The Calliope Hummingbird overlaps extensively in range with the Rufous Hummingbird (Selasphorus rufus) but is generally less aggressive and noticeable and thus more likely to be overlooked on migration.
At life's extremes in size and performance, basic principles are more obvious and thus more advantageously studied. Ironically, the biology of the Calliope Hummingbird has not attracted the measure of scientific inquiry that it deserves. Consequently, knowledge of its life history is far from complete. The gaps represent several opportunities for further study.