Sunbirds are very small birds, 3 to 7 inches (8 to 16 centimeters) long, resembling New World hummingbirds. The males of most sunbird species are brilliantly colored with combinations of iridescent, metallic green, purple, blue and black along with spots and patches of yellow, orange and red. Males of a few species are more drab, as are the females of nearly all sunbird species, although females of some species bear a metallic sheen. Outside of the breeding season, males molt and revert to less gaudy plumage (feathers) resembling that of the female of the species.
Sunbirds can easily be mistaken for the New World hummingbirds, but the sunbirds are strictly Old World birds and are not in any way related to hummingbirds. Sunbirds and hummingbirds are vivid examples of convergence, through adaptive evolution, by which unrelated species come to resemble each other due to similar environmental pressures over long stretches of time. In the case of sunbirds and hummingbirds, feeding on nectar has been the major adaptive molding factor in the two families.
Many single species are confined to some small islands off Africa, India, or in Indonesia. Examples include the Seychelles sunbird, found only on the Seychelles Islands, and the Sâo Tomé sunbird, found on Sâo Tomé.
Sunbirds in the genus Nectarinia have long, thin, downcurved bills for reaching into flowers to sip nectar, much like the bills of hummingbirds and other nectar-feeding bird species among the asity-sunbirds (family Philepittidae) and Hawaiian honeycreepers. Species in genus Anthreptes, considered the most primitive of the genera, have short, straight bills and chiefly feed by gleaning (plucking) insects from leaves, although they add nectar and fruits to their diets. Species of the genus Aethopyga have short bills and are among the most brilliantly colored animals alive. Species of genus Arachnothera, the spiderhunters, have low-key green, yellow, and gray plumage and most have very long, downcurved bills.
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