The prothonotary warbler (Protonotaria citrea) is a small songbird of the New World warbler family. It is the only member of the genusProtonotaria.The nature most beautiful bird prothonotary warbler is 13 cm long and weighs 12.5 g. It has an olive back with blue-grey wings and tail, yellow underparts, a relatively long pointed bill and black legs. The adult male has a bright orange-yellow head. Females and immature birds are duller and have a yellow head. In flight from below, the short, wide tail has a distinctive two-toned pattern, white at the base and dark at the tip.