|
|
|
Aleutian Tern
Onychoprion aleutica
The Aleutian Tern illustrates the limit of our advanced technology and global reach. Although it was first described in 1868, its wintering grounds remain a mystery and much of its life history is unknown. Its closest North American relatives may be the Bridled and Sooty Terns, and all three species are small, nimble flyers and denizens of the open ocean.
Measuring 12 inches long with a 29 inch wingspan, the Aleutian Tern weighs only 3.9 ounces. In breeding plumage, this fairly small seabird is grey over most of its body with a white tail and underwing. Contrasting with the white forehead and face, the black cap and bill connect through a thick line passing through the black eye. The short legs are also black. In nonbreeding plumage, the Aleutian Tern is grey above and white below. Its black cap withdraws to cover the back of the head and the nape and to just touch the back of the eye with a thin, black strip. In flight, this tern appears deep chested and flies directly, with deep wing beats.
In North America, this tern breeds only in Alaska from the Kasegaluk Lagoon along the northwest coast to Glacier Bay on Alaska's southern coast. Colonies are not faithful to one coastal site but are found most often from Point Hope south around the Seward Peninsula and into the Yukon-Kuskokwim River Delta, Cape Newenham, the Alaska Peninsula, and predator- free Aleutian Islands. Colonies are also scattered at several sites along the Siberian coast. The winter range and migratory routes are unknown. Observations in the 1990's suggest that it winters and/or migrates near the coasts of Hong Kong, Singapore, and several Indonesian Islands (Karimun, Bintan, Java, Bali and Sulawesi).
During the breeding season and perhaps for migratory staging, the Aleutian Tern lives over coastal waters. Here, it forages over shallow, oceanic waters, estuaries, rivers, and freshwater ponds. Breeding colonies require remote locations with even terrain: islands, tundra, arctic and subarctic meadows, river deltas, and sandy spits. A variety of vegetation may provide some concealment for nests: grasses, sedges, deep moss, low shrubs, and rushes. The nonbreeding habitat is probably the open ocean.
Like all terns, this able fisherman locates prey by sight as it courses over, hovers above, or sits on the water. Small fish, krill, shrimp, marine worms, and isopods are plucked from the water's surface or captured in a plunge dive. Near nesting sites, insects may be caught in flight. In spring and summer, the diet is mostly fish: sand lance, capelin, juvenile salmon, greenling, Pacific sandfish, and small polluck and cod fish. The winter diet has yet to be studied.
In early May, Aleutian Terns arrive on their breeding grounds and immediately form pairs. Courtship displays have rarely been observed, but all terns are known to engage in ritualized flights, feeding, and walking. In loose colonies near the coast, regularly mixed with other tern species like the Arctic Tern, the Aleutian Tern makes a simple bowl nest by depressing grasses, sedge, sand, or even fine gravel. The nest is sometimes lined with grass stems. Both sexes have brood patches and probably take turns incubating 1-3 light yellow eggs, marked with dark brown speckles and blotches. In about 3 weeks, the downy hatchlings emerge capable of leaving the nest, if necessary. Two weeks after hatching, the young hide in nearby vegetation and fledge at 1 month old. The parents continue to feed them through the fall, when juveniles gather before migration.
In late summer, this tern departs North America, where only a few linger into September. Fall migrants have been observed off the coast of Hong Kong as early as the third week in August, but they do not stay through October. Spring migrants are seen again off Hong Kong, as well as the Philippine Islands and the coast of Japan, in April and early May. Whether it travels in large or small flocks, by day or night, is unknown.
North, M. R. 1997. Aleutian Tern (Sterna aleutica). In The Birds of North America, No. 291 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.
Sibley, David Allen. 2000. The Sibley Guide to Birds. Alfred A. Knopf, New York.
32,500
22,000
Because colonies shift and, after breeding, the terns disperse to unknown parts of the world, counting Aleutian Terns accurately has been impossible. Alaska is estimated to host 9,500 breeding Aleutian Terns. Local population declines have been dramatic in Alaska. The breeding population on Kodiak Island's southern and eastern coastline dropped from 1,559 terns at the end of the 1970's to 2 individuals in 2002. Overall, Aleutian Terns are believed to be declining.
Although it lives far from population centers, our human society can still touch the Aleutian Tern. Dropped inadvertently from ships in the 18th century, rats now infest dozens of Alaska's islands, at least 18 of which are in the Alaskan Maritime N.W.R.(AMNWR), where the Aleutian Tern breeds. In 1750, arctic and red foxes were introduced to the Aleutian Islands for fur production, and between 1920 and 1930 at least 86 islands hosted free-ranging foxes, whose principle food source in the spring and summer was breeding seabirds. Throughout the 19th and 20th Centuries, the result of these infestations was the widespread collapse of all seabird colonies on many islands.
The eradication of foxes and rats from its breeding grounds may have already benefited this tern, but no studies have quantified the gains. Fox eradication began in the early 1970's and continues to this day, with some success. For example, in the AMNWR, foxes are no longer present on Adak and Avatanak Islands. Alaska's "Rat Plan" went into the trial phase in 2007 and is scheduled for implementation in 2008.
Aleutian Terns have also been affected by chronic oil spills, the disruption of colonies by humans, and natural predators concentrated by roads and villages. The U.S. Fish & Wildlife Service designated it as a Bird of Conservation Concern in 2002 and listed it as a Focal Species in 2006. Alaska included the Aleutian Tern in its 2006 Comprehensive Wildlife Strategy, which calls for long-term monitoring and censuses, the discovery of its winter quarters, and predator removal.
If the Aleutian Tern does winter over the near-shore waters of Southeast Asia, then a host of potential and existing problems may affect it, including coastal development, over-fishing, the destruction of coral reefs, and pollution. Perhaps the greatest conservation issue for the Aleutian Tern today is adequate monitoring of its remote, little-known, and scattered populations.
If you live or vacation in Alaska, support the state and federal effort to eradicate predators that humans have introduced to the Aleutian Tern's habitat. To learn more visit Stop Rats! and the Alaska Maritime National Wildlife Refuge's page on Invasive Species .
U.S. National Wildlife Refuges provide important habitat for the Aleutian Tern and a great number of other species throughout the U.S. and its territories. Unfortunately, the refuge system is often under-funded during the U.S. government's budgeting process. To learn more about how you can help gain much needed funding for U.S. National Wildlife Refuges, visit Audubon's refuge report.
Audubon's Important Bird Area program is another tool for the conservation of Aleutian Terns as well as other species special to Alaska. Read about the Important Bird Areas program in Alaska and how you can help with the IBA program.
Find out about actions you can take including Audubon programs and activities.
The U.S. Geological Survey tracks the spread of Avian Flu through wild waterfowl and seabirds. It has selected the Aleutian Tern as part of its monitoring program.
Learn more about this species and other birds through these resources.
Alaska Department of Fish and Game. " Aleutian Tern" (Appendix 4) in Our Wealth Maintained: A Strategy for Conserving Alaska's Diverse Wildlife and Fish Resources. April 2006. Alaska Department of Fish and Game, Juneau, Alaska. Accessed 26 August 2007.
" Aleutian Tern Onychoprion aleutica." Alaska Seabird Information Series. Branch Chief, Nongame Migratory Birds, Migratory BirdManagement, USFWS, 1011 E. Tudor Rd., Anchorage, Alaska. Accessed 26 August 2007.
Bailey, Edgar. " Introduction of Foxes to Alaskan Islands — History, Effects on Avifauna, and Eradication." Resource Publication 193: United States Department of the Interior, Fish and Wildlife Service, 1993, 56 pages. Accessed 27 August 2007.
Delany, S., and D. Scott, eds. 2006. Waterbird Population Estimates – Fourth Edition. Wetlands International, Wageningen, The Netherlands.
Hill, Norman F. and K. David Bishop. "Possible Winter Quarters of the Aleutian Tern?" Wilson Bulletin 111:4 (1999) 559-560.
North, M. R. 1997. Aleutian Tern ( Sterna aleutica). In The Birds of North America, No. 291 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.
|
|
|
|
