Animal Diversity Web

Ge­o­graphic Range

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)

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native

Habi­tat

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)

• Habitat Regions
• terrestrial

• Aquatic Biomes
• brackish water

• Wetlands
• marsh

• Other Habitat Features
• riparian
• estuarine

Phys­i­cal De­scrip­tion

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)

• Other Physical Features
• endothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Average mass

  260 g

  9.16 oz

• Range length

  390 to 420 mm

  15.35 to 16.54 in

Re­pro­duc­tion

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)

• Mating System
• cooperative breeder

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)

• Key Reproductive Features
• iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• oviparous

• Breeding interval

  Elegant terns breed once yearly

• Breeding season

  Breeding season takes place from early April to mid-June

• Average eggs per season

  1

• Average time to hatching

  26.1 days

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)

• Parental Investment
• male parental care
• female parental care

Lifes­pan/Longevity

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)

• Average lifespan
  Status: wild

  20.9 years

Be­hav­ior

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)

• Key Behaviors
• terricolous
• motile
• territorial
• social
• colonial

Home Range

El­e­gant terns choose nest­ing areas with the best vis­i­bil­ity, such as crests of steep slopes or flat areas. (Schaffner, 1982)

Com­mu­ni­ca­tion and Per­cep­tion

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)

• Communication Channels
• acoustic

• Other Communication Modes
• choruses

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

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)

• Primary Diet
• carnivore
  • piscivore

• Animal Foods
• fish

Pre­da­tion

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)

• Known Predators

  • Heermann's gulls (Larus heermanni), peregrine falcons (Falco peregrinus)

Ecosys­tem Roles

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)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known neg­a­tive eco­nomic im­pacts of el­e­gant terns on hu­mans.

Con­ser­va­tion Sta­tus

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)

• IUCN Red List

  Lower Risk - Near Threatened

Con­trib­u­tors

Ar­i­anne Leon (au­thor), Cal­i­for­nia State Uni­ver­sity, San Mar­cos, Tracey Brown (ed­i­tor), Cal­i­for­nia State Uni­ver­sity, San Mar­cos.

Ref­er­ences

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.

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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.