Evolution and systematics

Although ecological equivalents of the nonpasserine hummingbirds, sunbirds as passerines are quite unrelated to them. On morphological grounds, sunbirds were considered close relatives of the honeycreepers (Meliphagidae) and the white-eyes (Zosteropidae), but on the basis of analyses of their DNA, Sibley and Monroe (1990) placed them with the flowerpeck-ers and sugarbirds. Irwin (1999) revised the sunbirds and concluded that they are of African origin with the short-billed, mostly insectivorous, genera Deleornis, and Anthreptes being the most primitive.

Evolution of the long, curved bills associated with nectar-feeding members of Nectarinia and other genera probably came about as a consequence of seeking insects in flowers. In addition to Deleornis and Anthreptes, Irwin accepted the validity of the genera Chalcomitra, Cyanomitra, Cinnyris, and Leptocoma, which Delacour (1944) had grouped in Nectarinia. Other genera within the Nectariniidae currently recognized include Chalcoparia, Hedydipna, Hypogramma, Anabathmis, Dreptes, An-thobaphes, Drepanorhynchus, Aethopyga, and Arachnothera.

Some sources recognize 130 species in 16 genera, but Peters recognizes 5 genera and 117 species. The sunbirds have radiated into most habitats throughout sub-Saharan Africa and tropical Asia. They have also penetrated to extremely high altitudes on both continents: Gould's sunbird (Aethopyga goul-diae), for instance, breeds up to 14,100 ft (4,300 m). In order to cope with the freezing conditions they encounter on high mountains, some sunbirds have the ability to lower their body temperatures while roosting. There are close associations between some sunbirds and particular groups of plants. For example, there has been coevolution between genera of mistletoes and the long-billed sunbirds that pollinate them, and the orange-breasted sunbird (Anthobaphes violacea) is dependent on proteas and heaths in its fynbos habitat.

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