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Sterna sandvicensisSandwich tern

By Robert Gundy

Geographic Range

Sterna sandvicensis is considered a strictly coastal species although it may fly over large land masses during migration and inhabits some large inland lakes. In the Americas sandwich terns can be found as far north as the state of Virginia in the United States and extend southward to the northernmost parts of Chile on the western coast of South America and down to the southern reaches of Argentina along the east coast of the continent. In the Old World, sandwich terns can be found as far north as southern Sweden, extending south and west along the coast and wrapping around the tip of South Africa. Populations also exist in the Black and Caspian Seas, along the Persian Gulf and in Kenya, Tanzania and Djibouti in eastern Africa. (Birdlife International, 2009)

Habitat

Sandwich terns inhabit a variety of habitats including sandy or rocky oceanic beaches, oceanic cliff sides, estuaries and large inland lakes. Preferred nesting sites are usually sandy beaches with little or sparse vegetation or bare rock outcrops. (Birdlife International, 2009; Visser and Peterson, 1994)

Physical Description

Sandwich terns are medium-sized terns best identified by having a straight, slender black bill with a yellow tip and a black crown with a short crest. The underparts, rump and forked tail are white while the long, pointed wings and back are ash gray. The legs and webbed feet are black but can be varying degrees of yellow in one subspecies found in South America and the Caribbean. In non-breeding (winter) plumage the crown is mottled black and white to nearly all white and occasionally has black wing markings. In many migratory birds this change in plumage is thought to function as a sign to other birds of the same and similar species that the individual is not receptive to breeding.

Sandwich terns weigh between 130 and 311 g. They range from 36 to 46 cm in length and have a wingspan of 86 to 105 cm. (Birdlife International, 2009; Voelker, 1996)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    130 to 311 g
    4.58 to 10.96 oz
  • Range length
    36 to 46 cm
    14.17 to 18.11 in
  • Range wingspan
    86 to 105 cm
    33.86 to 41.34 in

Reproduction

Sandwich terns mate in monogamous pairs within large, densely packed nesting colonies that can reach numbers in the tens of thousands. This species typically nests alongside other species, most notably the common black-headed gull in western Europe. Often Sterna sandvicensis does not initially colonize a given area, rather it does not arrive until another species has already done so.

Upon arrival to colonial sites, adult birds will begin their rituals of attracting a mate or re-establish a relationship with a previous partner. Courtship displays include a male catching one or more fish and lining them side-by-side in its bill and presenting them to the female. She may immediately consume the fish or the two may engage in an aerial display soon after the initial presentation. Copulation in this family of birds is done by the male mounting behind the female on one side. The female will move her tail to the opposite side and the male will try to engage cloacal contact while using his wings to awkwardly maintain balance. (Birdlife International, 2009; Fasola and Canova, 1992; Fuchs, 1977)

Suitable nesting habitats include sandy or muddy beaches and open rock outcrops. Sandwich terns often return to colonial sites they have previously occupied before unless the habitat is deemed unsuitable. Nest sites are typically higher above the high tide line than the amount of ground actually available. Vegetation is generally avoided and mating pairs may abandon their nest sites if growing vegetation invades. Individual nests are simple concave scrapes in the substrate often lined with excrement.

Female sandwich terns lay 1 to 3 eggs per breeding season that incubate for 21 to 29 days. Birds at higher latitudes often begin laying eggs in May whereas lower latitudes begin in December. At hatching the young weigh 22 to 24 g. After 7 to 14 days some colonies will form crèches where young birds gather in large groups when parents are absent in order to gain safety in numbers. The ability to fly, or fledging, comes after 28 to 35 days. During their first year, young sandwich terns learn to catch food on their own by watching adults and practicing. Practice may include diving for actual food items or inanimate objects in order to gain accuracy. Sandwich terns reach sexual maturity at 3 to 4 years old. (Birdlife International, 2009; Fasola and Canova, 1992; Visser and Peterson, 1994)

  • Breeding interval
    Sandwich Terns breed once yearly.
  • Breeding season
    Sandwich Terns breed in the summer.
  • Range eggs per season
    1 to 3
  • Average eggs per season
    1-2
  • Range time to hatching
    21 to 29 days
  • Range fledging age
    28 to 35 days
  • Average time to independence
    1 years
  • Range age at sexual or reproductive maturity (female)
    3 to 4 years
  • Range age at sexual or reproductive maturity (male)
    3 to 4 years

After eggs have been laid, both parents share incubating responsibilities. Both parents take turns protecting the nest or foraging for the young. Parents continue to feed young until they are fledged and able to gather food on their own. After 7 to 14 days some colonies will form crèches where young birds gather in large groups when parents are absent in order to gain safety in numbers. (Birdlife International, 2009; Dunn, 1972; Fuchs, 1977; Stienen, et al., 2001)

  • Parental Investment
  • precocial
  • male parental care
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

The oldest recorded sandwich tern lived to be 23 years and 7 months. (Birdlife International, 2009)

  • Average lifespan
    Status: captivity
    23.58 years

Behavior

These birds are often silent much of the time and are usually only noticed by sight. They can be frequently seen flying along the shallows of a coastline and occasionally dive-bombing prey. When resting they will often form small groups and face away from the wind. If a neighbor gets too close short squabbles tend to unfold until one assumes dominance. This species is migratory, sometimes traveling great distances from breeding to wintering grounds. Migration may be southward or northward depending on the location of breeding grounds. Individuals that breed in western Europe will travel south along the western coast of Africa. Individuals from the Black Sea will stay in the Black Sea or move to the Mediterranean. Caspian Sea individuals winter in the northern Indian Ocean and Persian Gulf. North American individuals travel south to the Caribbean and down through Central and South America. (Birdlife International, 2009)

Home Range

Traveling 10 to 15 km per day in search of food is common in this species with reports extending as far as 70 km per day. (Birdlife International, 2009)

Communication and Perception

It may be inferred from the studies on royal terns that nesting adult sandwich terns are able to distinguish their own eggs by visual cues alone. Sandwich terns are able to recognize their own young by visual cues and vocalizations. Young are often called out of a crèche by parents, showing that the young can also identify their parents by vocalization. Sandwich terns perceive their environment through visual, tactile, auditory, and chemical stimuli. (Hutchison, et al., 1968)

Food Habits

Sandwich terns are known to eat reef silverside, dwarf round herring, Atlantic thread herring, hardhead silverside, scaly sardines, common anchovies, mackerel, jacks, flying fish, damselfish, parrotfish, Atlantic herring, sprat, lesser sand eel and squid. The adults feed chicks different prey species than they themselves prefer to eat. It is not clear if this is due to different dietary needs of young versus adults. In instances where this species has become accustomed to human interaction, adults will occasionally accept bread. (Shealer, 1998; Stienen and Brenninkmeijer, 2002)

These birds typically do not form large feeding flocks but will gather in small groups or hunt alone. They fly several meters above the water while foraging for prey. Once prey item is spotted they first hover above with beaks aimed directly downward in order to set their aim then dive-bomb into the water. First-winter birds are often less successful in catching food for themselves than older adults. (Dunn, 1972; Shealer, 1998)

  • Animal Foods
  • fish
  • mollusks

Predation

Short-eared owls, carrion crows, herring gulls, great black-backed gulls, foxes, and stoats are predators of chicks while common black-headed gulls prey mostly on eggs. Sandwich terns display little aggressive anti-predator behaviors. Densely situated nesting sites with more aggressive species of bird tend to alleviate the necessity for defensive behaviors. If necessary, sandwich terns will show defensive displays involving spreading their wings and raising their bodies to appear larger and mobbing or dive-bombing potential predators. Most of this aggressive behavior is seen during the breeding season when chicks are beginning to hatch. (Fuchs, 1977)

Ecosystem Roles

There appears to be a mutualism between sandwich terns and common black-headed gulls where the latter provides protection from predators while occasionally eating the eggs and stealing prey items of the former. (Stienen and Brenninkmeijer, 2002; Stienen, et al., 2001)

Mutualist Species

Economic Importance for Humans: Positive

Inshore fisherman will often look for diving terns in order to locate small baitfish.

Economic Importance for Humans: Negative

There are no known adverse effects of sandwich terns on humans.

Conservation Status

This is a species of Least Concern from the International Union of the Conservation of Nature due to its large numbers and geographic distribution. The suitability of a given habitat for creating nesting colonies of sandwich terns is vulnerable to destruction by natural phenomena events (ie: hurricanes, storms) and vegetation overgrowth. Habitat destruction by humans is known to adversely affect the ability of this species and many others that depend on undisturbed beach to breed. Overuse by humans visiting beaches can cause whole colonies to abandon the area en masse and minimize re-use in future years. (Visser and Peterson, 1994)

Other Comments

In 2009 a DNA study separated the three subspecies of Sterna sandvicensis into two distinct species. The North American forms are combined as one under the name Thalasseus acuflavidus and the European form as Thalasseus sandvicensis. As of yet this suggestion has not been fully adopted by the scientific community. (Efe, et al., 2009)

Contributors

Robert Gundy (author), Florida State University, Emily DuVal (editor), Florida State University, Rachelle Sterling (editor), Special Projects.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

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.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

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.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

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.

female parental care

parental care is carried out by females

iteroparous

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).

male parental care

parental care is carried out by males

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

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

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

young precocial

young are relatively well-developed when born

References

Birdlife International, 2009. "Sterna sandvicensis" (On-line). IUCN Red List of Threatened Species. Accessed January 14, 2010 at http://www.iucnredlist.org/apps/redlist/details/144242/0.

Buckley, P., F. Buckley. 1972. Individual Egg and Chick Recognition By Adult Royal Terns (Sterna maxima maxima). Animal Behaviour, 20: 457-462.

Dunn, E. 1972. Effect of Age on the Fishing Ability of Sandwich Terns Sterna sandvicensis. Ibis, Vol. 114, Issue 3: 360-366.

Efe, M., E. Tavares, A. Baker, S. Bonatto. 2009. Multigene phylogeny and DNA barcoding indicate that the Sandwich tern complex (Thalasseus sandvicensis, Laridae, Sternini) comprises two species. Molecular Phylogenetics and Evolution, Vol. 52, Issue 1: 263-267.

Fasola, M., L. Canova. 1992. Nest Habitat Selection by Eight Syntopic Species of Mediterranean Gulls and Terns. Colonial Waterbirds, Vol. 15, No. 2: 169-178.

Fuchs, E. 1977. Predation and Anti-Predator Behaviour in a Mixed Colony of Terns Sterna sp. and Black-headed Gulls Larus ridibundus with Special Reference to the Sandwich Tern Sterna sandvicensis. Ornis Scandinavica, Vol. 8, No. 1: 17-32.

Gochfeld, M., J. Burger. 1996. Family Sternidae (Terns). Pp. 647 in J del Hoyo, A Elliott, J Sargatal, eds. Handbook of the Birds of the World, Vol. 3. Hoatzins to Auks. Barcelona: Lynx Edicions.

Hutchison, R., J. Stevenson, W. Thorpe. 1968. The Basis for Individual Recognition by Voice in the Sandwich Tern (Sterna sandvicensis). Behaviour, Vol. 32, No. 1: 150-157.

Shealer, D. 1998. Differences in Diet and Chick Provisioning between Adult Roseate and Sandwich Terns in Puerto Rico. The Condor, Vol. 100, No. 1: 131-140.

Stienen, E., A. Brenninkmeijer, C. Geschiere. 2001. Living with Gulls: The Consequences for Sandwich Terns of Breeding in Association with Black-headed Gulls. The International Journal of Waterbird Biology, Vol. 24, No. 1: 68-82.

Stienen, E., A. Brenninkmeijer. 2002. Foraging Decisions of Sandwich Terns in the Presence of Kleptoparasitising Gulls. The Auk, Vol. 119, No. 2: 473-486.

Visser, J., G. Peterson. 1994. Breeding Popluations and Colony Site Dynamics of Seabirds Nesting in Louisiana. Colonial Waterbirds, Vol. 17, No. 2: 146-152.

Voelker, G. 1996. An Hypothesis for Seasonal Color Change in the Genus Sterna. Journal of Avian Biology, Vol. 27, No. 3: 257-259.

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