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Short-tailed Albatross (Phoebastria Albatrus)

Biology

General

Very little quantitative information exists on the biology of the Short-tailed Albatross. Like all pelagic seabirds, the species spends most of its life at sea, returning to land only to breed. They are long-lived birds that are slow to mature, and breeding females produce a single egg per year. This is balanced by a low natural rate of adult mortality (Cochrane and Starfield 1999). The average generation time is estimated to be 26 years (cf. a mean of 24.2 years, range 15-30, for 13 other albatross species; P. Sievert pers. comm. 2003).


Reproduction

Short-tailed Albatrosses are monogamous, and most adult birds with surviving mates breed annually. Individuals that lose a mate may require two or more years to form a new pair bond and nest successfully again. Pairs return to nearly identical nest sites each year, and in general birds hatched on Torishima return to the island to breed. 

For the Torishima colony, the age of first breeding is estimated to be 6 years (Sievert and Hasegawa 2003). This is younger than for other albatross species, and may result from the low density of individuals in the colony, compared with historically high breeding densities (Cochrane and Starfield 1999). Approximately 50% of the population is considered sexually mature (i.e. 6 years or older) (H. Hasegawa 2001, in litt), and of those an estimated 75% breed each year (Sievert and Hasegawa 2003). From 1976 the average annual breeding success (the percent of eggs laid that result in a fledged chick) has been high at around 64% (Sievert and Hasegawa 2003). Low breeding success has been recorded in years when catastrophic volcanic (1988) or weather events (1995) have occurred during the breeding season, thus introducing a greater variability in breeding success than for some other albatross species (Cochrane and Starfield 1999).

On Torishima, individuals begin arriving at the breeding colony in October and begin nest building. Egg-laying occurs from late October through early November. A single egg is laid, incubation is shared by both parents and lasts for 64-65 days. Eggs are not replaced if destroyed (Austin 1949). Hatching occurs from late December through early January. By late May or early June, chicks are almost fully grown and adults begin abandoning their nests. Chicks fledge soon after the adults leave the colony, and do not return until they are non-breeding two-to-five year olds (Hasegawa and DeGange 1982). Non-breeders and failed breeders disperse from the breeding colony in late winter through spring. While there is no detailed information on breeding activities on Minami-kojima, they are likely to be similar to those on Torishima.


Survival

For the Torishima colony, the annual adult survival rate is estimated to be 96.7%, and that of immature birds (all birds under the age of first breeding) is 94.1% (Sievert and Hasegawa 2003). No confidence intervals are available. No references are available on annual variation within age classes (Cochrane and Starfield). Longevity is not known for this species although Hasegawa (in Cochrane and Starfield 1999) estimates individuals may live to be 50 years or older.

Little information is available on the causes of natural mortality in Short-tailed Albatrosses (Hasegawa and DeGange 1982). Losses of eggs or chicks through desertion, storms, interference from other albatrosses, accidental egg puncturing, disease, parasites and the rolling of eggs from nests are potential, but unquantified, sources of mortality (Hasegawa and DeGange 1982). Harrison (1979) suggests that sharks may get some hatch-year birds after they have fledged. Adults and chicks are known to die when they have become entangled in bushes or other similar vegetation (Austin 1949). 


Movements/Dispersal

Little is known of the seasonal movements of the Short-tailed Albatross. Historically, it was presumed that after the birds departed from their colonies, the majority dispersed towards the Aleutians and the Bering Sea, with many moving down along the west coast of North America, some as far south as Baja (McDermond and Morgan 1993). 

Sightings during the past 30 years indicate that during the breeding season (December through April) the distribution of both adults and immatures is concentrated near the breeding colonies in the Izu and Bonin Islands (McDermond and Morgan 1993), although foraging trips may extend hundreds of miles or more from the colony sites (Federal Register 2000). Recent research indicates that immature individuals exhibit two patterns of post-breeding dispersal: while some move relatively rapidly north to the western Aleutian Islands, other individuals stay within the coastal waters of northern Japan and the Kuril Islands, Russia, throughout the summer. In early September these individuals move through the Kuril Islands and into the western Aleutian Islands. Once in the Aleutians, most birds travelled east toward the Gulf of Alaska (Suryan et al. 2003).

Outside the breeding season, the majority of adults reported have been observed near the Aleutians (Camp 1993, McDermond and Morgan 1993, Sherburne 1993). Regardless of season, proportionally more immatures (than adults) have been observed in the eastern and northern regions of the Pacific. These results are mirrored by those presented for Canadian waters (see above sections). This suggests that young birds wander farther (than adults) and for longer periods (McDermond and Morgan 1993).


Nutrition and Interspecific Interactions

As for with of the albatrosses, the Short-tailed is a surface feeder (Prince and Morgan 1987) and may feed nocturnally (Hasegawa and DeGange 1982, Sherburne 1993).  Although there is very little published information, the diet of the species is known to include squid, fish, eggs of flying fish, shrimp and other crustaceans (Prince and Morgan 1987, Federal Register 2000). The nestling diet varies but squid, flying fish and large crustacea are the most important foods (Hasegawa and DeGange 1982). There is currently no information on variation of diet by season, habitat, or environmental condition (Federal Register 2000). 

While a number of the Short-tailed Albatross sightings at sea have also noted the presence of other seabird species in association with them, including other albatross, fulmars, kittiwakes and shearwaters (Lane 1962, Wyatt 1963, Tramontano 1970, Wahl 1970, Camp 1993, Cochrane and Starfield 1999), the degree of interspecific interaction or competition, if any, is unknown. Such reports are usually associated with fishing vessels, and it may be that each species is attracted to fishing activity independently.


Behaviour/Adaptability

Short-tailed Albatrosses were known to follow whaling vessels and feed on offal and scraps from whale carcasses. Although they are considered somewhat “‘shy” Short-tailed Albatross still follow ships (Wahl 1970, Gruchy et al. 1972, Yesner 1976, Hasegawa and DeGange 1982). As with many other seabirds, the presence of “free food” in the form of offal and bait also attracts Short-tailed Albatross to fishing operations. Associated with this behaviour is the risk of mortality from incidental take in the longline fishery (see sections below).

Historically Short-tailed Albatrosses rafted together in the waters around Torishima (Austin 1949), and small groups have occasionally been observed at sea (Camp 1993). An oil spill or more likely, an intentional discharge of oily bilge, in an area where a large number of individuals were rafting could affect the population significantly (Federal Register 2000).

The Short-tailed Albatross is highly mobile, with a large marine range. This likely makes the species adaptable to seasonal and inter-annual changes in its prey distribution.