A dust-like substance resembling talcum powder is present on the contour feathers of many birds. Sexual selection can involve intersexual selection but not intrasexual selection. Birds generally produce 5 to 14 distinct calls having a variety of communicative functions. One function of apteria appears to be to aid the bird in losing excess body heat.
Some birds use tools to assist their feeding activities.
Learning is not important for most songbirds to achieve the complete song of their species. A large vocal repertoire appears to enhance a male bird's reproductive success. Especially because of biochemical data, the hoatzin is now placed in the order Sphenischiformes. Vocal mimicry is one way that some birds enlarge their vocal repertoires. Some birds can produce two sets of sounds simultaneously because the vocal apparatus consists of two independent halves.