Hind toe present or wanting. Toes only partially webbed or not webbed at all. Sternum has two notches usually on each side of posterior margin, but several species have only one on each side. Tibia with but few exceptions bare for some distance above tibio-tarsal joint. Schizognathous, or birds with vomer narrow behind, pointed in front; maxillo palatines free. Nostrils in a groove or depression. Oil-gland tufted. Primaries eleven. Fifth secondary wanting. After-shaft. Young are hatched covered with down. Eggs double-spotted.