Sterna antillarum
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The least tern (''Sternula antillarum'') is a species of
tern Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae which includes gulls and skimmers and consists of e ...
that breeds in North America and locally in northern
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
. It is closely related to, and was formerly often considered conspecific with, the
little tern The little tern (''Sternula albifrons'') is a seabird of the family Laridae. It was formerly placed into the genus ''Sterna'', which now is restricted to the large white terns. The genus name is a diminutive of '' Sterna'', "tern". The specific ' ...
of the Old World. Other close relatives include the yellow-billed tern and Peruvian tern, both from South America. It is a small tern, long, with a wingspan of , and weighing . The upper parts are a fairly uniform pale gray, and the underparts white. The head is white, with a black cap and line through the eye to the base of the bill, and a small white forehead patch above the bill; in winter, the white forehead is more extensive, with a smaller and less sharply defined black cap. The bill is yellow with a small black tip in summer, all blackish in winter. The legs are yellowish. The wings are mostly pale gray, but with conspicuous black markings on their outermost
primaries Primary elections, or direct primary are a voting process by which voters can indicate their preference for their party's candidate, or a candidate in general, in an upcoming general election, local election, or by-election. Depending on the c ...
. It flies over water with fast, jerky wingbeats and a distinctive hunchback appearance, with the bill pointing slightly downward. It is migratory, wintering in
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
, the Caribbean and northern South America. Many spend their whole first year in their wintering area. It has occurred as a vagrant to
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
, with one record in
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It i ...
and one in
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
. It differs from the little tern mainly in that its rump and tail are gray, not white, and it has a different, more squeaking call; from the yellow-billed tern in being paler gray above and having a black tip to the bill; and from the Peruvian tern in being paler gray above and white (not pale gray) below and having a shorter black tip to the bill.


Subspecies

The differences among the three subspecies may not be as much as had been thought. * ''S. a. athalassos'' – (Burleigh & Lowery, 1942): Breeds on the rivers of the
Arkansas River The Arkansas River is a major tributary of the Mississippi River. It generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's source basin lies in the western United Stat ...
,
Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...
, Brazos River, Trinity River, and Rio Grande basins; winters south to northern
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. * ''S. a. antillarum'' – (
Lesson A lesson or class is a structured period of time where learning is intended to occur. It involves one or more students (also called pupils or learners in some circumstances) being taught by a teacher or instructor. A lesson may be either one ...
, 1847)
:
nominate Nomination is part of the process of selecting a candidate for either election to a public office, or the bestowing of an honor or award. A collection of nominees narrowed from the full list of candidates is a short list. Political office In the ...
, Breeds on the
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
coast of North America, from
Maine Maine () is a state in the New England and Northeastern regions of the United States. It borders New Hampshire to the west, the Gulf of Maine to the southeast, and the Canadian provinces of New Brunswick and Quebec to the northeast and ...
south along the east and south coasts of the United States,
Bermuda ) , anthem = "God Save the King" , song_type = National song , song = "Hail to Bermuda" , image_map = , map_caption = , image_map2 = , mapsize2 = , map_caption2 = , subdivision_type = Sovereign state , subdivision_name = , es ...
, the Caribbean, and
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...
; winters south to northern
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
. * ''S. a. browni'' – ( Mearns, 1916):
California least tern The California least tern, ''Sternula antillarum browni'', is a subspecies of least tern that breeds primarily in bays of the Pacific Ocean within a very limited range of Southern California, in San Francisco Bay and in northern regions of Mexico ...
. Breeds on the
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
coast of North America, from central
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
south to western
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
; winters mainly in
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
. Additionally, least terns of an unknown subspecies were found in 2012 nesting on the Big Island of
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
.


Conservation and status


''S. a. antillarum''

The population is about 21,500 pairs; it is not currently considered federally threatened, though it is considered threatened in many of the states in which it breeds. Threats include egg and fledgling predators, high tides and recreational use of nesting beaches.


''S. a. athalassos''

The interior subspecies, with a current population of about 7000 pairs, was listed as an endangered subspecies in 1985 (estimated 1000 breeding pairs), due to loss of habitat caused by
dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
s,
reservoirs A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...
, channelization, and other changes to river systems. It was delisted on 13 January 2021.


''S. a. browni''

The western population, the
California least tern The California least tern, ''Sternula antillarum browni'', is a subspecies of least tern that breeds primarily in bays of the Pacific Ocean within a very limited range of Southern California, in San Francisco Bay and in northern regions of Mexico ...
, was listed as an endangered species in 1972 with a population of about 600 pairs. With aggressive management, mainly by exclusion of humans via fencing, the Californian population has rebounded in recent years to about 4500 pairs, a marked increase from 582 pairs in 1974 when census work began, though it is still listed as an endangered subspecies. The California subspecies breeds on beaches and bays of the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...
within a very limited range of southern California, in San Francisco Bay and in northwestern
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
. While numbers have gradually increased with its protected status, it is still vulnerable to predators, natural disasters or further disturbance by humans. Recent threats include the
gull-billed tern The gull-billed tern (''Gelochelidon nilotica''), formerly ''Sterna nilotica'', is a tern in the family Laridae. It is widely distributed and breeds in scattered localities in Europe, Asia, northwest Africa, and the Americas. The Australian gull ...
(''Sterna nilotica''), which can decrease reproductive success in a colony to less than 10%.


Nesting and breeding behavior

The least tern arrives at its breeding grounds in late April. The breeding colonies are not dense and may appear along either marine or estuarine shores, or on sandbar islands in large rivers, in areas free from humans or predators.
Courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
typically takes place removed from the nesting colony site, usually on an exposed tidal flat or beach. Only after
courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
has confirmed mate selection does nesting begin by mid-May and is usually complete by mid-June. Courtship takes the form of either an aerial display in which the female follows the flight of the male or through courtship feeding. Nests are situated on barren to sparsely vegetated places near water, normally on sandy or gravelly substrates. In the southeastern United States, many breeding sites are on white gravel rooftops. In the San Francisco Bay region, breeding typically takes place on abandoned salt flats. Where the surface is hard, this species may use an artificial indentation (such as a deep dried footprint) to form the nest basin. The nest density may be as low as several per acre, but in
San Diego County San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the f ...
, densities of 200 nests per acre have been observed. Most commonly the clutch size is two or three, but it is not rare to consist of either one or four eggs. Adults are known to wet themselves and shake off water over the eggs when arriving at the nest. Both female and male incubate the eggs for a period of about three weeks, and both parents tend the semiprecocial young. Young birds can fly at age four weeks. After formation of the new families, groupings of birds may appear at
lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
settings in proximity to the coast. Late-season nesting may be renests or the result of late arrivals. In any case, the bulk of the population has left the breeding grounds by the end of August. File:lagoonb.jpg, Batiquitos Lagoon, a breeding site in
San Diego County San Diego County (), officially the County of San Diego, is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, making it California's second-most populous county and the f ...
, California File:Nesting least terns Missouri River.jpg, Nesting pair on the Missouri River in
South Dakota South Dakota (; Sioux: , ) is a U.S. state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota and Dakota Sioux Native American tribes, who comprise a large porti ...
File:Core Banks - Black Skimmer chased by Least Tern - 02.JPG, A least tern attacking a much larger black skimmer near Drum Inlet in
North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and ...
, United States File:Least Tern (Sternula antillarum) RWD3.jpg, Mating pair at Sunset Beach, North Carolina File:Least Tern Mating Sequence.jpg, The mating sequence of a pair of least terns processed into one image ( St. Augustine, Florida) File:Least Tern on Nest with Two Eggs Visible.jpg, This least tern is on the nest. There are two eggs which can be seen if one looks closely. File:Two Least Tern Eggs in Typical Shallow Nest.jpg, The eggs are speckled and generally blend well with the sandy surface. File:Least Tern on Nest.jpg, A least tern lying just below the surface of the sand is probably on its nest. The nests are very shallow and minimally scooped out. File:First Fish Feeding1.jpg, First fish feeding at
Quintana, Texas Quintana is a town in Brazoria County, Texas, Brazoria County, Texas, United States. Its population was 56 at the 2010 census. Geography Quintana is located in southern Brazoria County at , on Quintana Beach along the Gulf of Mexico. It is bordere ...
File:Least Tern Chicks Day 2.jpg, Two-day-old chicks File:Least Tern Day Seven.jpg, Seven-day-old chicks File:LkJacksonFLTernMay2004.JPG, Least tern (''S. a. antillarum'') at Lake Jackson, Florida


Feeding and roosting characteristics

The least tern hunts primarily in shallow
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
and
lagoons A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
, where smaller fishes are abundant. It hovers until spotting
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
, and then plunges into the water without full submersion to extract meal. The most common prey recently for both chicks and adults are silversides smelt ('' Atherinops'' spp.) and anchovy ('' Anchoa'' spp.) in southern California, as well as shiner perch, and small
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
s elsewhere. Adults in southern California eat kelpfish (most likely giant kelpfish, ''Heterostichus rostratus''). Insects are known to be eaten during
El Niño El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date ...
events. In southern California, least terns feed in bays and lagoons, near shore, and more than from shore in the open ocean. Elsewhere, they feed in proximity to lagoons or bay mouths. Adults do not require cover, so that they commonly roost and nest on the open ground. After young chicks are three days old, they are brooded less frequently by parents and require wind blocks and shade, and protection from predators. In some colonies in southern California, Spanish roof tiles are placed in colonies so chicks can hide there. Notable disruption of colonies can occur from predation by
burrowing owl The burrowing owl (''Athene cunicularia''), also called the shoco, is a small, long-legged owl found throughout open landscapes of North and South America. Burrowing owls can be found in grasslands, rangelands, agricultural areas, deserts, or an ...
s,
gull-billed tern The gull-billed tern (''Gelochelidon nilotica''), formerly ''Sterna nilotica'', is a tern in the family Laridae. It is widely distributed and breeds in scattered localities in Europe, Asia, northwest Africa, and the Americas. The Australian gull ...
s and
American kestrel The American kestrel (''Falco sparverius''), also called the sparrow hawk, is the smallest and most common falcon in North America. It has a roughly two-to-one range in size over subspecies and sex, varying in size from about the weight of ...
s. Depredation by domestic cats has been observed in at least one colony. Predation on inland breeding terns by coyotes, bobcats, feral dogs and cats, great blue herons, Mississippi kites, and
owl Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers a ...
s has also been documented.


References

* * * * Gary Deghi, C. Michael Hogan, et al., ''Biological Assessment for the Proposed
Tijuana Tijuana ( ,"Tijuana"
(US) and
< ...
/San Diego Joint International Wastewater Treatment Plant'', Publication of the U.S. Environmental Protection Agency Region IX, Earth Metrics Incorporated, Burlingame, CA with Harvey and Stanley, Alviso, CA *


External links


Least tern Photo Field Guide on Flickr
* * * *
Tern Colony: an individual-based model of Least Tern reproduction
{{Taxonbar, from=Q28168
least tern The least tern (''Sternula antillarum'') is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the little tern of the Old World. Ot ...
Birds of the United States Birds of Mexico Birds of the Caribbean Birds of the Dominican Republic Fauna of the San Francisco Bay Area
least tern The least tern (''Sternula antillarum'') is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the little tern of the Old World. Ot ...
Taxa named by René Lesson