Nectar-feeding is widespread among birds, but no species consumes nectar exclusively. Most combine it with insectivory for a mixed diet. Of particular interest are three lineages of specialized nectarivorous birds: the hummingbirds (Trochili dae), sunbirds (Nectariniidae) and honeyeaters (Meliphagidae). Nectar is produced by flowering plants to attract pollinators to visit the flowers and transport pollen between them. Flowers often have specialized structures that make the nectar accessible.