Tropicbirds

(Phaethontidae)

Class Aves

Order Pelecaniformes

Suborder Phaethontes

Family Phaethontidae

Thumbnail description
Medium-sized oceanic birds with pointed wings, highly elongate central tail-feathers, an overall white coloration with black markings on the wings, and excellent flight skills

Size
29–40 in (74–100 cm); includes elongated tail streamers; wingspread 37–44 in (94–112 cm)

Number of genera, species
1 genus; 3 species

Habitat
Coastal and offshore waters of warm-temperate and tropical oceans

Conservation status
Not threatened, although some populations are declining

Distribution
Breed on isolated tropical islands; range widely in tropical and warm-temperate waters around the world, often far offshore

Evolution and systematics

There are only the three species of tropicbirds (genus Phaethon) in the family Phaethontidae. They are related to other waterbirds in the order Pelecaniformes, including pelicans, frigatebirds, cormorants, gannets, and anhingas. The Pelecaniformes lineage is ancient, with a fossil record extending to the Lower Eocene (54 million years ago).

Physical characteristics

Tropicbirds are medium-sized seabirds with a slightly decurved and pointed bill, long pointed wings, and highly elongate tail streamers (rectrices, the two central tail feathers). Body length is about 29–40 in (74–100 cm); this includes the tail streamers, which can be up to 21 in (53 cm) long and comprise about half the total body length. Wingspan is 37–44 in (94–112 cm), and the weight is 0.7–1.7 lb (0.30–0.75 kg). The plumage is overall white, sometimes with a pink flush, and black wing markings, a black eye-line, and sometimes a darker back (depending on the species). The bill is colored yellow to orange-red. Adults have elongate, narrow tail streamers. Young birds lack the tail streamers and have a gray-white banded back and wings. The short legs are placed far back on the body, making walking awkward. The feet are webbed as an aid in swimming. There is no obvious external physical difference between male and female tropicbirds.

Distribution

Tropicbirds range widely in coastal waters of tropical and warm-temperate regions, sometimes occurring far offshore. They breed on isolated tropical islands such as Ascension Island in the Indian Ocean, Cousin Island in the Seychelles group, and Kauai in the Hawaiian Islands.

Habitat

Tropicbirds breed on isolated tropical islands. When not breeding, they range widely in coastal and offshore tropical and warm-temperate waters.

Behavior

Tropicbirds have a steady, pigeon-like flight, often settling on the surface of the water to rest. They use their webbed feet as rudders during flight, and sometimes hover in breeding displays. They do not walk well, and often shuffle on their belly when on land. They catch much of their food of small fish and marine invertebrates by making shallow plunge-dives, often from an impressive height. They have a tern-like voice and can be noisy around the breeding colonies, but are generally silent when at sea outside of the breeding season.

Feeding ecology and diet

Tropicbirds generally search for food singly or in pairs, but may also associate with large flocks of other seabirds. They often catch small flying-fish above the surface. They also feed on other species of small fish, squid, and larger

crustaceans caught at the water surface, or by making a shallow plunge-dive. The typical size of prey selected is determined by the size of the bill; in areas where two species of tropicbirds occur, they tend to partition food on the basis of bill size.

Reproductive biology

Tropicbirds usually nest on ledges of coastal cliffs, in cavities under rocks, or under vegetation that gives protection

from the sun and rain. On some Pacific islands, they nest in trees. Ground nests are a shallow scrape and are usually located together in colonies. The social courtship display includes groups of birds flying excitedly and noisily around the nesting site in undulating flight. During this display flight, the long tail feathers wave conspicuously up and down. Tropicbirds lay only one egg, which is initially colored mottled reddish or brown but becomes paler with time as the water-soluble pigment is lost due to moisture and rubbing. The chick hatches after an incubation period of 41–45 days. The chick has a dense, silky, gray or yellow-brownish down plumage that gives protection against intense sunlight. It is fed by both parents, beginning at an age of three days, and takes 11–15 weeks to fledge. Chicks are vulnerable to being killed by adults of the same or related species of tropicbirds that are seeking a scarce nesting site. Among the redbilled and white-tailed tropicbirds of Ascension Island, such interactions within and between the two species can result in a low survival rate of young and the evolution of complex differences in breeding timetables. Red-billed tropicbirds breed every year on Ascension Island, but white-tailed tropicbirds

breed every nine months and may do so at any time of the year.

Conservation status

Tropicbirds are not listed as being at risk globally by the IUCN or in the United States by the Fish and Wildlife Service. Although general population trends are not well known, some local breeding populations have declined because of disturbance and habitat loss, and perhaps because of mortality associated with commercial drift-net fishing.

Significance to humans

Tropicbirds are not of much economic importance to humans, although they are appreciated by naturalists and this can contribute to local economic benefits through ecotourism.

Formerly, tropicbird feathers were sold to the once-prominent business of millinery, or the production of women's hats and garments. The long tail feathers are still used as traditional adornments in various island cultures. The human consumption of tropicbirds, including eggs and chicks, has occurred since ancient times.

Species accounts

List of Species

White-tailed tropicbird

Phaethon lepturus

taxonomy

Phaeton lepturus Daudin, 1802, Mauritius.

other common names

English: Golden bosunbird, yellow-billed tropicbird; French: Phaéton à bec jaune; German: Weißchwanz-Tropikvogel; Spanish: Rabijunco Menor.

physical characteristics

Adult body length (including streamers) is 29 in (74 cm), wingspan 37 in (94 cm), and weight 11 oz (0.30 kg). The overall body color is white, with black markings on the upper wings, a black eye-stripe, and a reddish (rarely yellow) bill. Juveniles have a pale-cream bill.

distribution

Tropical and warm-temperate oceans of the world.

habitat

Tropical and warm-temperate oceans of the world, especially in coastal waters.

behavior

An excellent flier that commonly feeds by shallow plunge-dives and by catching flying-fish on the wing. They have a rattling call in flight, and seldom glide.

feeding ecology and diet

Small fish, squid, and larger marine invertebrates, which are caught above, at, or just under the water surface. Tends to feed closer to shore than other species of tropicbirds.

reproductive biology

Breeds on remote tropical islands. A single egg is laid and incubated by both adults. Chicks have white, buff-gray, or blue-gray down. Fledging in 70–85 days.

conservation status

Not threatened.

significance to humans

None known.

Red-billed tropicbird

Phaethon aethereus

taxonomy

Phaethon aethereus, Linnaeus, 1758, Ascension Island.

other common names

English: Silver bosunbird; French: Phaéton à brins rouges; German: Rotschwanz-Tropikvogel; Spanish: Rabijunco Colirrojo.

physical characteristics

Adult body length (including streamers) is 18 in (46 cm), wingspan 44 in (112 cm), and weight 1.6 lb (0.75 kg). The overall body color is white, with black markings on the upper wings, a darker back, a black eyestripe, red tail-streamers, and a bright red bill. Juveniles have a black bill.

distribution

Tropical and warm-temperate oceans of the western Pacific Ocean, especially off western Mexico and the Galápagos Islands, the tropical Atlantic Ocean, and the Red Sea region of the northwestern Indian Ocean.

habitat

Tropical and warm-temperate waters, especially in coastal areas.

behavior

An excellent flier that feeds by shallow plunge-dives and by catching flying-fish on the wing. The voice is a harsh, clanging rattle.

feeding ecology and diet

Small fish, squid, and larger marine invertebrates, which are caught above, at, or just under the water surface.

reproductive biology

Breeds on remote tropical islands. A single egg is laid and incubated by both adults. Chicks have gray down, fledge at 80–90 days.

conservation status

Not threatened.

significance to humans

Not of much importance to humans, except for the economic benefits of ecotourism related to birdwatching.

Resources

Books

Harrison, P. Seabirds. An Identification Guide. Beckenham, United Kingdom: Croom Helm Ltd., 1983.

Orta, J. "Family Phaethontidae (Tropicbirds)." Handbook of the Birds of the World. Vol 1, edited by J. del Hoyo, A. Elliott, and J. Sargatal. Barcelona: Lynx Edicions, 1992.

Periodicals

Howell, T. R., and G. A. Bartholomew. "Experiments on Nesting Behavior of the Red-tailed Tropicbird, Phaethon rubricauda." Condor 71 (1969): 113-119.

Stonehouse, B. "The Tropicbirds (Genus Phaethon) of Ascension Island." Ibis 103b (1962): 126-161.

Organizations

BirdLife International. Wellbrook Court, Girton Road, Cambridge, Cambridgeshire CB3 0NA United Kingdom. Phone: +44 1 223 277 318. Fax: +44-1-223-277-200. E-mail: [email protected] Web site: <http://www.birdlife.net>

Bill Freedman, PhD