Red-billed Tropicbird

The red-billed tropicbird measures 90 to 105 cm (35 to 41 in) on average, which includes the 46 to 56 cm (18 to 22 in)-long tail streamers. Without them the tropicbird measures about 48 cm (19 in). It has a wingspan of 99 to 106 cm (39 to 42 in). In overall appearance it is tern-like in shape. Its plumage is white, with black wing tips, and a back that is finely barred in black. It has a black mask that extends up from just above the lores to the sides of its nape, with gray mottling usually seen near the nape and hindneck. The tail has black shaft streaks, as do tail streamers. The underparts are white, with some black on the outermost primaries and tertials and occasionally with black markings on the flanks. The iris is blackish-brown, and the bill is red. The legs, base of the central toe, and parts of the outer toes are orange-yellow while the rest of the feet are black. Although the sexes are similar, the males are generally larger than females, with the tail streamers being around 12 cm (4.7 in) longer on the male than on the female. The subspecies of this bird can usually be distinguished by their difference in size and plumage. The subspecies Phaethon aethereus mesonauta can be differentiated by its slightly rosy tinge when its plumage is fresh, the bolder look of the black barring on the upper wing, and the more solid look of the black on the outer wing. The subspecies P. a. indicus can be distinguished by its smaller size, its smaller mask on the face, which often does not extend far behind the eye, and its more orange bill with a black cutting edge. When the chicks hatch, they are covered with gray down. This down is eventually cleared in about 40 to 50 days. The young chicks lack tail streamers. The juvenile looks similar to the adult with a mostly white crown. In the juvenile, the stripes above the eye usually are connected at the nape. The tail feathers usually have black tips or subterminal dots and without the tail streamers that are distinctive on the adult. Occasionally, a juvenile will have black markings on its flanks and under tail coverts. The red-billed tropicbird can be differentiated from the other tropicbirds by its red bill in combination with its white tail streamers. The slightly smaller red-tailed tropicbird has red rather than white tail streamers, and the white-tailed tropicbird can be differentiated by its smaller size, black stripe along its upper wing coverts, and its yellow-orange bill. Juvenile red-billed tropicbirds have more heavily barred upper parts than juveniles of other species. In flight, the royal tern can be confused with the adult red-billed tropicbird but can be distinguished by the former's less direct flight pattern and its lack of tail streamers. This tropicbird moults once every year as an adult, following a complex basic strategy. This prebasic moult is completed before courtship and lasts between 19 and 29 weeks, with most being completed in 24 weeks. Birds gain their adult plumage at two to three years of age. The red-billed tropicbird usually only calls near breeding colonies, where it joins in with groups of other adults, numbering from 2 to 20, in circling above the sea and making loud, harsh kreeeee-kreeeee-kri-kri-kri-kr screams. If disturbed at the nest, the chicks will vocalize a loud and piercing shriek, either rasping or reeling.