BioKIDS home

Kids' Inquiry of Diverse Species

Caspian tern

Sterna caspia

What do they look like?

Caspian terns are the largest tern species and are recognized by their large, bright coral red bill and full black cap on the head. Sexes are alike, from 47 to 54 cm long and from 530 to 782 g. Their upperparts are smooth gray and their breast, belly, rump, and tail are white. The wing feathers are dark gray to black on the underside. Their black cap might be speckled with white during the non-breeding season and in juveniles. The tail is only slightly notched. They have a large bill that is deep red to orange, sometimes with dark gray mark at the tip.

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    530 to 782 g
    18.68 to 27.56 oz
  • Range length
    47 to 54 cm
    18.50 to 21.26 in

Where do they live?

Caspian terns have a cosmopolitan distribution, they are found on all continents except Antarctica. They are found along coastlines of oceans, seas, large lakes, and rivers. They migrate between breeding and wintering ranges for the most part, although some populations are resident year-round. In the Americas, Caspian terns breed along coastal and inland waterways from the Gulf of Mexico and Baja California northwards through the Great Lakes and Canadian interior and as far north as southern Alaska on the Pacific coast and the Canadian maritime provinces on the Atlantic coast. They winter from southern California to Guatemala along the Pacific coast, including the Gulf of California, and from southern North Carolina on the Atlantic coast to Panama and Venezuela, including the Gulf of Mexico.

What kind of habitat do they need?

Caspian terns are found in coastal areas, including beaches, marshes, estuaries, or in open habitats on islands in large bodies of water. They forage over water and nest on sandy, muddy, or pebbly shores or areas with little vegetation on islands.

How do they reproduce?

Caspian terns form mated pairs that stay together for the breeding season. Some pairs remain together for many years, but only 25% of pairs mate again the next year in some populations. Pairs are formed soon after birds arrive on the breeding grounds, although some pairs form during migration or on the wintering range. Males attract mates with a "fish flight." Males capture a fish and then fly with it over a group of terns. Females and males join in the display, flying with the male as he repeatedly passes over the group. He then lands near a female and makes bowing movements with his head. Females may ignore the male, try to steal the fish, or beg for the fish. Pairs perform a "high flight" display together to cement the bond, ascending and diving together as they vocalize. Symbolic construction of nest scrapes is also part of the courtship ritual.

Caspian terns arrive on the breeding grounds from late March to late May. Pairs begin to form nest scrapes soon after they arrive on the breeding grounds. They breed in late May and early June, laying from 1 to 3 buffy, splotched eggs. Eggs are laid every 2 to 3 days in a simple depression scraped in the ground and incubation begins immediately with the first egg. Caspian terns have 1 brood yearly. Incubation is from 25 to 28 days and young begin to fly at 37 days after hatching. Most individuals don't breed until they are 3 years old.

  • How often does reproduction occur?
    Caspian terns breed once yearly.
  • Breeding season
    Caspian terns breed in late May or June.
  • Range eggs per season
    1 to 3
  • Range time to hatching
    25 to 28 days
  • Average fledging age
    37 days
  • Range age at sexual or reproductive maturity (female)
    2 (low) years
  • Average age at sexual or reproductive maturity (female)
    3 years
  • Range age at sexual or reproductive maturity (male)
    2 (low) years
  • Average age at sexual or reproductive maturity (male)
    3 years

Both parents incubate the eggs. A parent will bring a fish and offer it to their mate on the nest, then take over incubating. Females tend to spend more time caring for eggs and young. Parents protect their young from heat by standing above them to provide shade. Young are semiprecocial when hatched, with downy feathers but relying on their parents for feeding. They remain in or near the nest for about a week after hatching. They are fed fish by parents soon after hatching and they begin to accompany parents on foraging trips within a week or so of learning to fly.

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

How long do they live?

As in most other animals, most deaths occur within a few months of hatching. Adults have high survival rates and can live more than 26 years in the wild.

How do they behave?

Caspian terns are awkward on the ground, waddling to walk. They are powerful and graceful in flight and can dive rapidly to capture fish. Caspian terns roost overnight and nest in groups of just a few individuals to many hundreds. They prefer to nest in places where there are fewer predators, especially islands. Nesting colonies can be very dense with terns in areas that are safest from predators. They may be active at any time of the day, but most foraging seems to be concentrated in the morning hours. Caspian terns aggressively defend the small area around their nest. Some Caspian tern populations migrate and others are resident. The timing of migration varies, depending on the region. In general, they begin migrating south from July to September. Most populations arrive on the breeding grounds in March through May. Caspian terns migrate alone or in groups of up to thousands of individuals.

  • Range territory size
    0.5 to 1.5 m^2

Home Range

Caspian terns defend small areas around their nests in the nesting colony. Nest territories are 0.5 to 1.5 meters squared. However, some pairs nest alone and defend larger territories, even entire small islands. Occasionally individuals will defend small foraging areas. (Cuthbert and Wires, 1999)

How do they communicate with each other?

Caspian terns, like most terns, use a variety of calls. Young begin to call from within the egg and use an "i-i-i" call to beg for food. Caspian terns use various calls to maintain contact, express alarm, advertise that they are bringing fish back to the nest, and to beg. Most calls are hoarse and sound like "ra" or "rau." During courtship, they make steep dives that produce a soft, buzzing sound with their wings. Caspian terns communicate through visual displays and body posturing as well.

What do they eat?

Caspian terns eat mainly fish, with some crayfish and insects occasionally. They forage by flying above shallow water, usually along a shoreline. As most terns do, they fly with their heads down, peering into the water, when they see prey, they may hover for a moment before making a sharp dive. They may just skim the surface when they dive or they may almost completely submerge themselves for a few seconds. They usually eat their prey as soon as it is captured but may take some fish back to a nest. They may wash fish before offering it to young and often clean their bill in water after feeding young. Fish prey includes shiner perch, anchovies, alewives, rainbow smelt, yellow perch, rock bass, jacksmelt, topsmelt, staghorn sculpin, and juvenile salmon.

  • Animal Foods
  • fish
  • insects
  • aquatic crustaceans

What eats them and how do they avoid being eaten?

Most predation is on eggs and hatchlings, which may be taken by a wide variety of predators. Reported predators on eggs and hatchlings include gulls, great horned owls, common ravens, domestic cats, dogs, coyotes, red foxes, striped skunks, raccoons, northern pike, and western diamondback rattlesnakes. Adult Caspian terns may fall prey to birds of prey, such as bald eagles, and terrestrial predators when roosting or on a nest, such as coyotes and red foxes. When a predator approaches a nesting colony, Caspian terns raise an alarm call and will often join together to mob the predator. They are aggressive and will chase any large bird that is close to a colony. Their diving attacks can be very effective, resulting in bloody wounds. However, their habit of taking flight to mob a predator may also leave eggs and nestlings vulnerable. Predators sometimes grab eggs and nestlings from exposed nests when the adults have flown away. Chicks crouch in the nest scrape and difficult to see, but will be detected by predators using scent or warmth to find prey.

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

Caspian terns are predators of small or young fish in coastal areas, they may be especially important predators in areas near breeding colonies. Caspian terns must compete for limited nesting habitats, including competing with gull species. Caspian terns are parasitized by lice and internal worms.

Species (or larger taxonomic groups) that are mutualists with this species
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host
  • nematode (Cosmocephalus species)
  • lice (Actornithophilus funebre)
  • lice (Degeeriella praestans)
  • lice (Menophon)
  • lice (Philopterus melanocephalus)
  • cestodes (Dibothriocephalus oblongatum)
  • cestodes (Schistocephalus solidus)
  • cestodes (Paricterotaenia species)
  • trematodes (Diplostomum species)
  • trematodes (Cotylurus species)
  • trematodes (Ornithobilharzia species)
  • trematodes (Clinostomum species)
  • trematodes (Stephanoprora species)

Do they cause problems?

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

How do they interact with us?

Caspian tern eggs were once collected for food. They are colorful and fascinating members of native coastal faunas worldwide. (Cuthbert and Wires, 1999)

  • Ways that people benefit from these animals:
  • food

Are they endangered?

Caspian tern populations have declined in some parts of their range, especially in Europe and Africa where some populations have gone extinct. Populations in North America have increased because measures were taken to protect breeding areas and habitat. They are considered threatened in some states, including Michigan. They are considered "least concern" by the IUCN Red List because of their large geographic range and population sizes.

Some more information...

Contributors

Tanya Dewey (author), Animal Diversity Web.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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

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.

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.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

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

animals that generate their own body heat through metabolic processes.

estuarine

an area where a freshwater river meets the ocean and the fresh and saltwater mixes

food

A substance that provides both nutrients and energy to a living thing.

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).

migratory

makes seasonal movements between breeding and wintering grounds

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.

sedentary

remains in the same area

sexual

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

social

associates with others of its species; forms social groups.

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

Cuthbert, F., L. Wires. 1999. Caspian Tern (Sterna caspia). The Birds of North America Online, 403: 1-20. Accessed April 22, 2009 at http://bna.birds.cornell.edu/bna/species/403.

 
University of Michigan Museum of ZoologyNational Science Foundation

BioKIDS home  |  Questions?  |  Animal Diversity Web  |  Cybertracker Tools

Dewey, T. 2009. "Sterna caspia" (On-line), Animal Diversity Web. Accessed April 19, 2014 at http://www.biokids.umich.edu/accounts/Sterna_caspia/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
Copyright © 2002-2014, The Regents of the University of Michigan. All rights reserved.

University of Michigan