It is extremely difficult to generalize about any of the behaviors or nesting habits of passerines, because as a group they are so diverse. Perching birds exhibit a bewildering array of plumages and colors derived from diverse keratin structures as well as ingested pigments, such as carotenoids (Gray, 1996). Many passerines, such as some Old World Flycatchers (Muscicapidae) and African Widowbirds (Viduinae) have extremely long tail feathers or highly modified plumes (Birds of Paradise: Paradisaeidae) used in courtship displays. Several groups such as the Wattlebirds of New Zealand (Callaeidae) and Honeyeaters (Meliphagidae) have fleshy, bright blue, red or yellow wattles on the face and neck. Perching birds build their nests generally out of sticks or grass on the ground, in trees, and in the case of Dippers (Cinclidae) in the banks of fast-flowing rivers. Many passerines migrate from their nesting grounds in the Nearctic and Palearctic to more equatorial regions, or from southern temperate regions north to the tropics. Parental care by both sexes is common in passerines, although in some highly dimorphic and predominantly lekking groups, such as manakins (Prum, 1994) and birds of paradise (Diamond, 1986), females alone provide for young and build the nest. Cooperative breeding, in which young birds delay breeding and assist other individuals (often parents) in raising young and defending the territory, is common in several passerine groups, such as Australian fairy wrens (Maluridae) and New World Jays (Corvidae; Brown, 1987; Edwards and Naeem, 1993). Some of the most elaborate singers in the bird world are passerines (Kroodsma and Miller, 1996). Some passerine birds are poisonous to the touch and are avoided as prey by indigenous peoples (Dumbacher et al., 1992).