During the winter months, elegant terns (Thalasseus elegans) range along the Pacific coast from Nayarit, Mexico to as far south as Puerto Montt, Chile. The breeding range of elegant terns extends throughout southern California, Baja California, and the Gulf of Mexico, with five known breeding colonies. Isla Rasa in the Gulf of California, Mexico is the largest colony, containing approximately 90 to 97% of breeding individuals. The smaller colony is found in the southern San Diego Bay, California at the Western Salt Company. Other small colonies breed in Bolsa Chica Ecological Reserve, California; almost three hundred pairs were found breeding at Isla Montague in the Gulf of California; as early as 1998 a colony of 3,000 pairs were established in the Los Angeles Harbor, California. In summer, after breeding season ends, elegant terns migrate north from the breeding colony at Isla Rasa, Mexico to central and northern California. Migrations to Oregon and south Washington occur, but are less frequent. Non-breeding ranges of elegant terns range from central California south to Costa Rica all along the Pacific coast. ("Check-list of North American Birds", 1983; Clapp, et al., 1993; Collins, 1997; Collins, et al., 1991; Devillers and Terschuren, 1977; Howell and Webb, 1995; Palacios and Mellink, 1993; Small, 1994; Tweit and Dix, 1990)
Elegant terns are only found off coasts on isolated beaches and on the islands of Isla Montague and Isla Rasa in the Gulf of California, where over 90% of individuals breed. Elegant terns also occupy estuaries when hunting or foraging for food. The beaches they occupy are flat and open, with mudflats available for them to use for roosting. There is little to no vegetation around their habitats. Elegant terns in San Diego Bay breed in ditches above the water created from muddy, salty sediment left behind from evaporated ponds. Non-breeding and migratory habitat of elegant terns consists of bays, harbors, lagoons and estuaries. (Anderson, 1983; Kirven, 1969; Schaffner, 1982)
Elegant terns are medium-sized sea birds in the family Laridae. Both males and females can grow anywhere from 390 to 420 mm in length and weigh approximately 260 g. They have long thin bills that are yellow to orangish-red in color. Their beaks are sometimes longer in length than their heads. During breeding season, their upper wings and backs are bluish-gray in color, which contrasts with their darker gray outer primaries. The rest of the plumage on their bodies is white with bits of pink on their undersides. Their tails are forked and their legs are mostly black in color with an occasional spotting of yellow and orange. During the breeding season elegant terns have a black cap on top of their heads and a shaggy crest that covers their foreheads and around their eyes. During non-breeding season the remaining black portion of their caps form a mask, beginning around their eyes and running back on top of their heads to nearly the base of their necks. However, their foreheads turn white in the non-breeding season. Juvenile elegant terns have gray crests instead of the shaggy black ones seen in adults. (Harrison, 1983; Olsen and Larsson, 1995)
Not much is known about the nesting and reproduction of elegant terns, but research speculates that their nesting and breeding patterns might be similar to that of Caspian terns, since they are usually found in similar nesting areas and habitats. Elegant terns court and form pairs either during migration or in their nesting colonies. A small group of terns that have found mates are called “clubs”. Clubs form adjacent to nesting colonies. They form anywhere from two to three weeks before eggs are laid. Nesting begins in April when mated pairs dig nests by scraping indentations in the ground. Elegant terns lay eggs within 24 hours of building their nests. Elegant terns require small, isolated nesting areas with other breeding terns or gull species in the vicinity. (Evans, 1973; Kirven, 1969; Schaffner, 1982)
Elegant terns usually lay only one egg per clutch, with 95% of the nests in San Diego Bay containing only one egg per mated pair. The level of parental care is moderate and equal to that that of many other tern and gull species. Parents take turns incubating their eggs. The incubating parent does not move or leave its nest unless switching nesting duties with its mate. Eggs hatch from early April to mid-June. When chicks are born they are covered in downy feathers, which camouflage chicks with the ground of the nesting sites. Chicks are able to walk around 4 days after being hatched and are able to fly at approximately 34 days after hatching, after which they are able to join mobs of adult terns. (Evans, 1973; Kirven, 1969; Schaffner, 1982)
Both male and female elegant terns in a mated pair incubate, but there is currently no data on relative amounts of time each spends on the nest. Parents relieve each other of incubation duties frequently during day. While incubating and brooding, elegant terns rarely leave their nests except to exchange nest duties with their mates. While one parent is nesting the other parent is out foraging. Parents never leave their nests unattended. (Evans, 1973; Kirven, 1969; Schaffner, 1982)
The current recorded lifespan of wild elegant terns is approximately 20.9 years, based on a small sample size of the birds and banding studies. No other information is currently known about their lifespan or longevity and more research is required. (Tacutu and et al, 2018)
Elegant terns have stronger flying skills than other species of terns and beat their wings rapidly while foraging. Despite living primarily near coasts, they only briefly swim, bathe, or preen in the water. They are mostly seen floating on the surface or on buoys. Elegant terns only preen after copulation. They sleep with their eyes closed, on their belly with their heads stretched forward and their bills resting on the ground. When they are resting they stay clustered in large groups, sometimes mixed with other flocks of species resting in the same area. On breeding grounds the adults roost at night in a colony, resting shoulder to shoulder. They do not roost in the water but rest on buoys during both the day and night. Elegant terns exhibit intraspecific competition mostly when establishing nesting grounds or when defending their chicks. They attack by locking their bills together or making repeated, rapid strikes with their bills in what is considered a “fencing” motion. They are territorial only with the area immediately surrounding their nests. (Monroe, Jr., 1956; Peterson and Peterson, 1991)
Elegant terns choose nesting areas with the best visibility, such as crests of steep slopes or flat areas. (Schaffner, 1982)
Elegant terns are considered a highly vocal and social species when interacting with others of their kind or going about their daily activities. When looking for nesting sites they are called “screaming masses” and a group of elegant terns that gather en masse and make noise is called a “spirited cacophony". The calls of adult elegant terns are low-pitched and more closely resemble calls of least terns or sandwich terns. Juveniles emit high-pitched squeaks when begging for food. Elegant terns give calls but none are considered songs. Not much else is currently known about calls made outside breeding season or of any call patterns. (Evans, 1973; Olsen and Larsson, 1995; Peterson and Peterson, 1991; Small, 1994; Walker, 1965)
The primary food source for elegant terns are schooling fish species comprised mostly of anchovies (family Engraulidae), sardines (family Clupeidae), silversides (family Atherinopsidae), gobies (family Gobiidae), and mackerels (family Scombridae). Northern anchovies (Engraulis mordax) are the main species of fish in their diet. When searching for food, elegant terns hover over the water and then dive into the surface when they spot prey. Elegant terns stop at locations called “clubs”, which are gatherings of terns so that they are able to communicate with each other and discover possible foraging sites. (Ashmole, 1963; Horn, et al., 1996; Schaffner, 1982; Schaffner, 1986; Velarde, et al., 1994)
The dense nesting and colony formation of elegant terns reduces the possibility of predation. Elegant terns also minimize predation by breeding in areas with more aggressive tern species. Other bird species are the only predators that elegant terns have, with their eggs and chicks suffering from predation from Heermann’s gulls (Larus heermanni) at Isla Rasa. Gull predation causes colonies to compress and causes excessive crowding, which then results in eggs being broken or lost from their nests. Caspian terns at San Diego Bay play a crucial role in keeping away gulls and other birds in the family Laridae at bay. Caspian terns and their chicks tend to be found somewhat nearby the elegant tern nesting sites, resulting in additional protection. In some cases, peregrine falcons (Falco peregrinus) have also been observed taking the eggs of elegant terns. (Anderson, 1983; Lindsay, 1966; Schaffner, 1982; Schaffner, 1985; Velarde, 1993)
There is competition for space between the elegant terns and endangered California least terns (Sterna antillarum browni) at Bolsa Chica, California. This competition for breeding space is perhaps due to a broad overlap in diet and foraging habits at locations that both species use for breeding grounds. At Isla Rasa, they often settle en masse in colonies with other species such as gull species. They establish territory and dominance by displacing the gulls and destroying their nests. The presence of elegant terns is tied to their predation on different subpopulations of anchovy in California. Northern anchovies (Engraulis mordax) occur in 3 subpopulations. Between the years of 1979 to 1983 there was a negative correlation in the abundance of elegant terns in San Diego Bay with the abundance of anchovy. El Niño weather phenomena impact both anchovy and elegant tern populations, causing birds to disperse farther north than usual in search of food. Ecosystem roles such as mutualistic relationships or commensalism have not been studied or observed in elegant tern populations. (Grinnell and Miller, 1944; Horn, et al., 1996; Schaffner, 1982)
Elegant terns are a valuable indicator of size and composition of fish stocks within their foraging ranges during nesting season. The economic importance of elegant terns has currently not been further studied or observed. (Schaffner, 1985; Schaffner, 1986)
There are no known negative economic impacts of elegant terns on humans.
As of the 1990s, elegant terns have been reduced to 1 major colony at Isla Rasa, Gulf of California which represents 90-97% of the global breeding population. They are currently designated "Lower Risk, Near Threatened" on the IUCN Red List. They are not yet facing a high risk of extinction. In 1995 elegant terns were designated as a "migratory nongame bird of management concern" in the U.S. This list is intended to: "stimulate a coordinated effort by Federal, State and private agencies to develop and implement comprehensive and integrated approaches for the management of selected species of nongame birds deemed to be in the most need of additional conservation actions.”
A sanctuary system was proposed to protect island wildlife in Gulf of California and the Mexican government declared their islands as wildlife refuges in 1978. The threats to coastal habitats near elegant tern breeding colonies has California considering plans to restore the wetlands of Bolsa Chica Ecological Reserve and establish a wildlife refuge in San Diego Bay. (Clapp, et al., 1993; Horn, et al., 1996; Stadtlander, 1994; "The 1996 IUCN Red List of Threatened Animals", 1996)
Arianne Leon (author), California State University, San Marcos, Tracey Brown (editor), California State University, San Marcos.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
helpers provide assistance in raising young that are not their own
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
parental care is carried out by females
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
uses sight to communicate
1983. Check-list of North American Birds. Washington, D.C., USA: American Ornithologists' Union.
1996. The 1996 IUCN Red List of Threatened Animals. Cambridge, U.K: World Conservation Monitoring Centre.
Anderson, D. 1983. The seabirds. Pp. 246-264 in T Case, M Cody, eds. In Island biogeography in the Sea of Cortez. Berkeley, CA, USA: Univ. of California Press..
Ashmole, N. 1963. The biology of the Wideawake or Sooty Tern Sterna fuscata on Ascension Island. Ibis, 103b: 297-364.
Clapp, R., F. Buckley, P. Buckley. 1993. Conservation of temperate North Pacific terns. Pp. 154-162 in K Vermeer, K Briggs, D Siegel-Causay, eds. The status, ecology, and conservation of marine birds of the North Pacific.. Ottawa: Can. Wildl. Serv. Spec. Publ..
Collins, C. 1997. Hybridization of a Sandwich and Elegant tern in California. Western Birds, 28: 169-173.
Collins, C., W. Schew, E. Burkett. 1991. Elegant Terns breeding in Orange County, California. American Birds, 45: 393-395.
Devillers, P., J. Terschuren. 1977. Some distributional records of migrant North American Charadriiformes in coastal South America (continental Argentina, Falkland, Tierra del Fuego, Chile and Ecuador). Le Gerfaut, 67: 107-125.
Evans, M. 1973. The reproductive ethology of the Caspian Tern (Hydroprogne caspia) breeding at San Diego Bay. San Diego, CA, USA: San Diego State University.
Grinnell, J., A. Miller. 1944. The distribution of birds of California. Pacific Coast Avifauna, 27: 1-608.
Harrison, P. 1983. Seabirds: An Identification Guide. Boston, MA, USA: Houghton Mifflin Company.
Horn, M., P. Cole, W. Loeffler. 1996. Prey resource base of the tern and skimmer colonies at Bolsa Chica Ecological Reserve, Orange County, and the Western Salt Works, South San Diego Bay. Carlsbad, CA, USA: U.S. Fish and Wildl. Serv..
Howell, S., S. Webb. 1995. A Guide to the Birds of Mexico and Northern Central America. NY, USA: Oxford University Press.
Kirven, M. 1969. The breeding biology of Caspian Terns (Hydroprogne caspia) and Elegant Terns (Thalasseus elegans) at San Diego Bay. San Diego, CA, USA: San Diego State College.
Lindsay, G. 1966. The Gulf Islands Expedition of 1966. Proceedings of the California Academy of Sciences, 30: 309-355.
Monroe, Jr., B. 1956. Observations of Elegant Terns at San Diego, California. Wilson Bulletin, 68: 239-244.
Olsen, K., H. Larsson. 1995. Terns of Europe and North America. Princeton, NJ, USA: Princeton Univ. Press..
Palacios, E., E. Mellink. 1993. Additional records of breeding birds from Montague Island, northern Gulf of California. Western Birds, 24: 259-262.
Peterson, S., B. Peterson. 1991. An elegant invasion of terns. Sea Frontiers, 37: 50-53.
Schaffner, F. 1982. Aspects of the reproductive ecology of the Elegant Tern (Sterna elegans) at San Diego Bay. San Diego, CA, USA: San Diego State University.
Schaffner, F. 1985. Royal tern nesting attempts in California: isolated or significant incidents?. Western Birds, 16: 71-80.
Schaffner, F. 1986. Trends in Elegant Tern and northern anchovy populations in California. Condor, 88: 347-354.
Small, A. 1994. California Birds: Their Status and Distribution. Vista, CA, USA: Ibis Publishing Company.
Stadtlander, D. 1994. Colonial seabirds and the Western Snowy Plover nesting in south San Diego Bay, 1993. Carlsbad, CA, USA: Bay and Estuary Program, U.S. Fish and Wildlife Service.
Tacutu, R., et al. 2018. "Human Ageing Genomic Resources: new and updated databases" (On-line). Accessed May 14, 2020 at http://genomics.senescence.info/species/entry.php?species=Thalasseus_elegans.
Tweit, B., D. Dix. 1990. The winter season: Oregon/Washington region (Fall 1990 report). American Birds, 45: 309-312.
Velarde, E. 1993. Predation of nesting larids by Peregrine Falcons at Rasa Island, Gulf of California, Mexico. Condor, 95: 706-708.
Velarde, E., M. Tordesillas, L. Vieyra, R. Esquivel. 1994. Seabirds as indicators of important fish populations in the Gulf of California. California Cooperative Oceanic Fisheries Investigations Report, 35: 137-143.
Walker, L. 1965. Baja's island of birds. Pac. Discovery, 18/3: 27-31.