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.
- Biogeographic Regions
- nearctic
- palearctic
- oriental
- ethiopian
- neotropical
- oceanic islands
- indian ocean
- atlantic ocean
- pacific ocean
- mediterranean sea
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.
- Habitat Regions
- temperate
- tropical
- terrestrial
- saltwater or marine
- Aquatic Biomes
- coastal
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.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
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.
- Mating System
- monogamous
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- oviparous
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.
- Parental Investment
- precocial
- male parental care
- female parental care
-
pre-fertilization
- provisioning
-
protecting
- male
- female
-
pre-hatching/birth
-
provisioning
- male
- female
-
protecting
- male
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- male
- female
-
protecting
- male
- female
-
provisioning
-
pre-independence
-
provisioning
- male
- female
-
protecting
- male
- female
-
provisioning
Lifespan/Longevity
The oldest recorded sandwich tern lived to be 23 years and 7 months.
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.
- Key Behaviors
- flies
- diurnal
- motile
- migratory
- territorial
- colonial
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.
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.
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.
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.
- Primary Diet
- carnivore
- 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.
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.
- Common black-headed gulls ( Larus ridibundus )
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.
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.
Additional Links
Contributors
Robert Gundy (author), Florida State University, Emily DuVal (editor), Florida State University, Rachelle Sterling (editor), Special Projects.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- 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.
- 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.
- monogamous
-
Having one mate at a time.
- 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).
- 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
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- young precocial
-
young are relatively well-developed when born
- male parental care
-
parental care is carried out by males
- female parental care
-
parental care is carried out by females
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- migratory
-
makes seasonal movements between breeding and wintering grounds
- 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
- 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.
- visual
-
uses sight to communicate
- acoustic
-
uses sound to communicate
- carnivore
-
an animal that mainly eats meat
- piscivore
-
an animal that mainly eats fish
- molluscivore
-
eats mollusks, members of Phylum Mollusca
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
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 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.