White-tailed tropicbird

White-tailed tropicbird
Scientific classification
Kingdom Information
Domain	Eukaryota
Kingdom	Animalia
Subkingdom	Bilateria
Phylum Information
Superphylum	Deuterostomia
Phylum	Chordata
Sub-phylum	Vertebrata
Infraphylum	Gnathostomata
Class Information
Superclass	Tetrapoda
Class	Aves
Sub-class	Neognathae
Infra-class	Neoaves
Order Information
Order	Phaethontiformes
Family Information
Family	Phaethontidae
Genus Information
Genus	Phaethon
Species Information
Species	P. lepturus
Population statistics
Population	>50,000 (1992 est.)
Conservation status	Least concern

White-tailed tropicbirds (Phaethon lepturus), commonly called "longtails" or "bosun birds" depending on the location, are seabirds of the family Phaethontidae, and found in the tropical waters of the Atlantic, Pacific, and Indian oceans.

Description

White-tailed tropicbirds are similar to terns, but are larger, with a body length of about 20 inches (excluding the tail feathers), a wing span of about 37 inches, and a body weight of between 10.5 and 26.4 ounces. The water-repellent plumage is white overall, with wings that have the four outer primaries black in color (but not to the tips), as well as a bold, black diagonal stripe running from the secondary coverts to nearly the end of the secondaries close to the body; this stripe will on some birds connect on the back, forming a "V" marking. The subspecies P. l. fulvus is sometimes called the "golden bosun" for the gold tinge on its plumage.

Characteristic are the two central tail feathers, white in color, which are sometimes longer in length than the body, and sometimes referred to as streamers. They wear out very quickly, so they are often replaced. They play a role in the courtship, and perhaps also as balance aids in flight.

The legs are short and set at the back of the body. The feet are very small, giving the birds an awkward method of movement on land as they can only push themselves their stomachs, and then only over short distances. The beak is tall, slender and downward-pointed; it is orange yellow to orange red in color.

Subspecies

• Phaethon lepturus ascensionis; Atlantic ocean, breeds on Fernando de Noronha and Ascension islands
• Phaethon lepturus catesbyi; Atlantic Ocean, breeds on various Caribbean islands and Bermuda
• Phaethon lepturus dorotheae; western Pacific, breeds on islands from Hawaii to New Caledonia
• Phaethon lepturus europae; Mozambique Channel, breeds on Europa Island
• Phaethon lepturus fulvus; Indian Ocean, breeds on Christmas Island
• Phaethon lepturus lepturus; Indian Ocean, breeds on various islands

Diet

They hunt fish and cephalopods, and usually from a dive into the water from a height of 75 feet or more, capturing prey at or just below the surface. Particularly common are flying fish and small squid, which can be taken in flight while barely skimming the surface.

Breeding

White-tailed tropicbirds become sexually mature at the age of 3-4 years. They breed on tropical islands where they form small colonies with little social interaction. The breeding grounds can be found on inaccessible cliffs or on on sandy shores, where nests can be hidden under vegetation. On Christmas Island, tropic birds even breed in trees in the mountainous interior of the island. Regionally, the breeding season is very different, with breeding on some islands taking place throughout the year, and other places limited to the spring and summer months.

Breeding is preceded by a spectacular courtship flight, involving climbing to altitude and diving, with both birds touching wingtips and tail feathers. Afterwards, the couple lands at a suitable nesting site and usually copulates immediately after landing. If the ground permits, a small hollow is dug for the egg. If suitable nesting sites are scarce, fighting for such places can occur, with opponents using their beaks to hack on the heads of each other. If an opponent is successful, the others who had previously nested on the spot must give up their egg or chick. Due to the fighting in some places only 30% of the breeds are successful. White-tailed tropicbirds also use this aggressiveness against other species: they sometimes successfully displace petrels and take over their nesting sites.

A single egg is laid, a mottled, dirty gray over white. The egg is incubated for 40 to 46 days by both partners. The chick is initially fed with pre-digested food that the parent birds regurgitates into the chick's throat. Over time the chick is left alone more often, with the intervals between feedings increasing, and at about 70 to 90 days of age it makes its first flight and does not return to the nesting site.

The maximum age of tropic birds is unknown, but in any case exceeds sixteen years.

Threats

Nesting on low ground or cliff faces near shorelines makes this species vulnerable to hurricanes, as demonstrated at Bermuda by Dean (1989) and Felix (1995), resulting in a large number of dead birds, as well as the elimination of up to 50% of nesting sites. Construction for human habitation and roads has further reduced nesting sites on the island, however, the installation artificial "longtail igloos" on public and private property has met with some success as the breeding count has increased.

Introduced pests have taken a toll. On Christmas Island the current problem is the introduced yellow crazy ant (Anoplolepis gracilipes).The islands on which these birds breed are often so remote that there were no mammals to fear. Later, sailors exposed cats and rats there, devastating the local fauna. On such islands, the breeding succeed only on inaccessible cliffs. A study on the Kure Atoll has revealed that in some years 100% of the eggs and chicks have been predated on by rats. On some locations it is the frigatebird (Fregata sp.), a specialist which harasses tropicbirds for their catch, robbing them in flight.