The red-tailed tropic bird (Phaethon rubricauda melanorhynchos) is geographically distributed in the Indian and Pacific Oceans (Boland et al., 2004; Le Corre et al., 2003; Spear and Ainley, 2000a; Spear and Ainley, 2000b). The species has white plumage and a red or orange beak (Veit and Jones, 2003; Boland et al., 2004). Studies have documented weight ranging from 600 g to 900 g (Le Corre et al., 2003; Boland et al., 2004).

The red-tailed topicbird belongs to a lineage of birds known as Phaethontidae (Boland et al., 2004; Spear and Ainley, 2005a; Spear and Ainley, 2005b). Phaethontidae includes three species of tropicbirds: Phaethon rubricauda (the red-tailed tropicbird), P. lepturus (the white-tailed tropicbird), and P. aethereus (the red-billed tropicbird). The three species are distributed throughout the tropical and subtropical regions of the Pacific Ocean (Spear and Ainley, 2005a; Spear and Ainley, 2005b). The tropicbirds are distinguished by having elongate tail feathers known as streamers (Boland et al., 2004), and in all species the sexes are monomorphic.

The most striking feature of the red-tailed tropicbird is its red tail streamers (Veit and Jones, 2003; Boland et al., 2004). The streamers range in length from 190 cm to 468 cm (Boland et al., 2004), but do not provide an aerodynamic benefit (Veit and Jones, 2003). Instead the streamers are used in courtship displays (Veit and Jones, 2003; Boland et al., 2004). Interestingly, the red-tailed tropicbird cannot produce the carotenoid pigments required to produce the red color of the streamers naturally. The species must absorb the carotenoids through their diet. Birds that are unable to obtain the food items with the necessary carotenoids have less colorful streamers. Additionally, some parasites inhibit the ability of an individual to properly absorb the pigments. One study has suggested that the color of the streamers is an indication of mate quality since an individual’s ability to forage and parasitic load can be determined from their streamers’ color (Boland et al., 2004).

Growth patterns of the tail streamers have been studied thoroughly (Veit and Jones, 2003, 2004). Each tail streamer grows to about the same length every year (Veit and Jones 2003), a process which takes about six months (Veit and Jones, 2004). However, the streamers are not grown simultaneously. Instead, one streamer is molted and grown after the other streamer has reached its full length (Veit and Jones, 2003; Veit and Jones, 2004). Therefore, there is often a size asymmetry between the two tails depending on the stage of growth and wear of each streamer (Veit and Jones, 2003).

Mating in the red-tailed tropicbird is monogamous (Boland et al., 2004) and occurs in the summer (Le Corre et al., 2003). Nesting typically occurs on oceanic islands (Boland et al. 2004) and eggs are laid between mid-November and late December (Le Corre et al., 2003). The clutch size is one egg (Boland et al., 2004) and the incubation period last about 42 days (Le Corre et al., 2003). Parental care of the hatchling is distributed equally (Boland et al., 2004), taking place between February and May for about 85 to 90 days (Le Corre et al., 2003).

The diet of the red-tailed tropic bird includes mostly fish and squid (Le Corre et al., 2003). Individuals typically forage alone (Le Corre et al., 2003; Speak and Ainley, 2005a) and use surface diving to obtain prey (Le Corre, 1997; Le Corre et al., 2003). Although diving is believed to be the only type of underwater locomotion in which the red-tailed tropicbird engages, one study suggests that individuals may also use their wings and hindlimbs to propel themselves deeper underwater (Le Corre, 1997).

Additional Information on the Skull

Click on the thumbnails below for labeled images of the skull in standard anatomical views.

Dorsal view	Lateral view	Ventral view

This specimen (FMNH 346039) was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Timothy Rowe of the Department of Geological Sciences, The University of Texas at Austin. Funding for scanning was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Rowe.

Lateral view of skull	Dorsal view of skull	Ventral view of skull

The specimen was scanned by Matthew Colbert on 22 March 2004 along the coronal axis for a total of 643 slices, each slice 0.174 mm thick with an interslice spacing of 0.174 mm.

Literature

Baumel, J. J., A. S. King, J. E. Breazile, H. E. Evans, and J. C. Vanden Berge (eds.). 1993. Handbook of Avian Anatomy: Nomina Anatomica Avium, Second Edition. Publication of the Nuttall Ornithological Club, number 23. Nuttall Ornithological Club, Cambridge, MA, 779 pp.

Boland, C. R. J., M. C. Double, and G. B. Baker. 2004. Assortive mating by tail streamer length in red-tailed tropicbirds Phaethon rubricauda breeding in the Coral Sea. Ibis 146:687-690.

Hedges, S. B., and C. G. Sibley. 1994. Molecules vs. morphology in avian evolution: the case of the "pelecaniform" birds. Proceedings of the National Academy of Sciences, USA 91:9861-9865.

Le Corre, M., Y. Cherel, F. Lagarde, H. Lormée, and P. Jouventin. 2003. Seasonal and inter-annual variation in the feeding ecology of a tropical oceanic seabird, the red-tailed tropicbird Phaethon rubricauda. Marine Ecology Progress Series 255:289-301.

Le Corre, M. 1997. Diving depths of two tropical pelecaniformes: the red-tailed tropicbird and the red-footed booby. The Condor 99:1004-1007.

Mayr, G. 2003. The phylogenetic affinities of the shoebill (Balaeniceps rex). Journal für Ornithologie 144:157-175.

Morrell, T. E., S. M. Aquilani. 2000. Nest-site characteristics of red-tailed tropicbirds on Rose Atoll, American Samoa. Journal of Field Ornithology 71:455-459.

Olson, S. L. 1985. A new genus of tropicbird (Pelecaniformes: Phaethontidae) from the middle Miocene Calvert Formation of Maryland, USA. Proceedings of the Biological Society of Washington 98:851-855.

Spear, L. B., and D. G. Ainley. 2005a. At-sea behavior and habitat use by tropicbirds in the eastern Pacific. Ibis 147:391-407.

Spear, L. B., and D. G. Ainley. 2005b. At-sea distributions and abundance of tropicbirds in the eastern Pacific. Ibis 147:353-366.

Veit, A. C., and I. L. Jones. 2004. Timing and patterns of growth of red-tailed tropicbird Phaethon rubricauda tail streamer ornaments. Ibis 146:355-359.

Veit, A. C., and I. L. Jones. 2003. Function of the tail streamers of red-tailed tropicbirds (Phaethon rubricauda) as inferred from patterns of variation. The Auk 120:1033-1043.

Links

Phaethon rubricauda melanorhynchos on Avibase - The Wold Bird Databse.

Tropicbirds on The Animal Diversity Web (The University of Michigan Museum of Zoology).

None available.