Elegant tern (Sterna elegans)
| Synonyms: | Thalasseus elegans |
|---|
| Kingdom | Animalia |
|---|---|
| Phylum | Chordata |
| Class | Aves |
| Order | Charadriiformes |
| Family | Laridae |
| Genus | Sterna (1) |
| Size | Length: 39 - 43 cm (2) Wingspan: 76 - 81 cm (2) |
| Weight | 186 - 300 g (2) |
Classified as Near Threatened (NT) on the IUCN Red List (1).
The elegant tern is a medium-sized and rather striking tern, with a black cap and a distinctive long, shaggy crest. The upperparts and wings are light grey, and the underparts white, often suffused with rosy pink on the belly (2) (3) (4). The beak is particularly long and slender, with a slight downward curve, and varies from yellow-orange in the female to bright orange-red in the male. The legs and feet are usually black, but in some individuals are orange. The tail is deeply forked. In non-breeding plumage, the elegant tern has a white forehead and crown, while juvenile birds are distinguished by the mottled upperparts, darker feathers on the wings and tail, and a shorter, paler beak (2) (3).
The elegant tern has the most restricted breeding range of any tern in North America, breeding at just a few sites along the Pacific coast, from southern California in the United States, to Baja California and the Gulf of California in Mexico. Over 90 percent of the global population nests on Isla Rasa in the Gulf of California, with smaller numbers at Bolsa Chica, San Diego Bay, and Los Angeles harbour (2) (3) (4) (5). Although the range has expanded northwards since the 1950s (4) (6), the species has disappeared from several former nesting sites in Mexico (2) (4).
After breeding, the elegant tern disperses north along the coast, to northern California and southern British Columbia, later moving south again to spend the winter along the Pacific coast of Central and South America, as far south as Chile (2) (3) (4) (6).
The elegant tern is a coastal species, foraging in inshore waters, estuaries, harbours, salt-ponds and lagoons, and nesting on flat, rocky islands or sandy beaches (2) (3) (4) (5).
A social bird, the elegant tern can often be seen foraging in flocks, although smaller foraging groups or solitary foraging may be more usual. When feeding in a flock, the elegant tern calls frequently with a distinctive ke-e-e-r. The diet consists mainly of fish, particularly northern anchovy (Engraulis mordax), as well as occasional crustaceans, with prey caught by hovering and then plunge-diving into shallow water (2) (3) (4) (6). The elegant tern is often the victim of piracy by other seabirds, which attack the tern to steal its prey (2) (3).
Breeding occurs between April and May (2) (3), the elegant tern nesting in dense colonies, often in the company of larger, more aggressive species such as Heermann’s gull (Larus heermanni) and Caspian terns (Sterna caspia), which may offer some protection against predators (3) (6). Nest-building and egg-laying are highly synchronised within the colony, occurring in most pairs within the same 24 hour period (2) (3). The elegant tern is thought to be monogamous, forming a pair bond through elaborate courtship displays. The nest consists of a shallow scrape on the ground, and a single egg is laid, which hatches after around 25 to 26 days (2) (3) (4) (6). Both the male and female help to incubate the egg and raise the chick. The young elegant tern leaves the nest after just a few days, joining other chicks in a ‘crèche’, where it is still fed by its parents (3) (4) (6). Although fledging may occur in 30 to 35 days (2), the young tern is dependent on the adults for up to six months, during which time it learns how to forage (3) (4). Breeding is thought to occur from around three years old (3).
In the past, the elegant tern has been greatly affected by egg-collecting, particularly on Isla Rasa (2) (5). Current threats include disturbance at nesting sites from urban development, tourism, predators such as rats, cats and feral dogs, and extensive mining for guano, as well as entanglement in fishing gear and competition with fisheries (2) (3) (4) (5).
The highly restricted breeding range of the elegant tern makes it particularly vulnerable (3) (4) (5) (6), and the species is also subject to large population fluctuations, thought to be caused by the effects of El Niño on prey abundance, and probably compounded by overfishing (3) (5). In particular, the breeding success and dispersal patterns of the elegant tern in southern California appear to be related to the availability of the northern anchovy. Rising coastal water temperatures may shift the abundance and distribution of this prey species, so impacting the elegant tern (3) (4). Climate change, with its potential effects on ocean temperatures and on the frequency and intensity of El Niño events, may therefore pose a great threat to elegant tern populations in the future.
The elegant tern’s main breeding colony at Isla Rasa became a sanctuary in 1964, helping to reduce egg-collecting and so successfully stem the tern’s population crash at this site (2) (3) (4). Further conservation measures recommended for the species include monitoring population trends, ensuring effective protection of all breeding colonies, taking measures to protect colonies from disturbance, and researching the links between climate, fisheries, prey availability and elegant tern breeding success (3) (4) (5). Wardening and regular patrols of nesting sites are needed in the breeding season, and measures need to be taken to protect colonies from tourists, such as providing roped trails (3) (4). The elegant tern has been relatively little studied in comparison to other tern species, and basic data is urgently needed on its biology, ecology, behaviour and population trends (3).
To find out more about the elegant tern and its conservation see:
- National Audubon Society - Elegant Tern:
http://web1.audubon.org/science/species/watchlist/profile.php?speciesCode=eleter - Birds of North America Online:
http://bna.birds.cornell.edu/bna/species/404
For more information on this and other bird species please see:
- BirdLife International:
http://www.birdlife.org
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: arkive@wildscreen.org.uk
- Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
- El Niño: a natural phenomenon that happens every 4 to 12 years, and lasts for several months, when upwelling of cold, nutrient-rich water does not occur. This causes the warming of ocean surface water off the western coast of South America and causes die-offs of plankton and fish. It also affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.
- Guano: accumulated droppings found where large colonies of animals such as seals, bats or birds occur; it is rich in plant nutrients.
- Incubate: to keep eggs warm so that development is possible.
- Monogamous: having only one mate during a breeding season, or throughout the breeding life of a pair.
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IUCN Red List (June, 2009)
http://www.iucnredlist.org - del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
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Burness, G.P., Lefevre, K. and Collins, C.T. (1999) The Birds of North America Online: Elegant Tern (Sterna elegans). Cornell Lab of Ornithology, Ithaca. Available at:
http://bna.birds.cornell.edu/bna/species/404 -
National Audubon Society - Elegant Tern (June, 2009)
http://web1.audubon.org/science/species/watchlist/profile.php?speciesCode=eleter -
BirdLife International (June, 2009)
http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3261&m=0 - Kaufman, K. (2001) Lives of North American Birds. Houghton Mifflin Harcourt, Boston, Massachusetts.