Sterna forsteri

A medium-sized (14-15 inches) tern, Forster’s Tern in summer is most easily identified by its solid black cap, deeply-forked tail, black-tipped orange bill, and pale wing tips. In winter, this species becomes duller on the head and face, becoming dark-billed and pale headed while retaining conspicuous black eye-patches. This species may be distinguished from the similarly-sized Common Tern (Sterna hirundo) by that species’ dark wing tips and (in winter) black hood. Male and female Forster’s Terns are similar to one another in all seasons. Forster’s Tern breeds in a number of widely-separated areas across North America, both inland (on the northern Great Plains and Great Basin region) and along the coast (on the Atlantic, Gulf, and Pacific coasts, as well as in the Great Lakes region). In winter, this species may be found along the coast from California and the Mid-Atlantic region south to Central America. Populations breeding in southern coastal areas generally migrate short distances, if at all. Forster’s Terns primarily breed in marshland habitats, being found both at inland freshwater marshes and at coastal salt marshes. In winter, this species may be found along the shoreline on sandy beaches, riverbanks, and mudflats. Forster’s Terns mainly eat small fish. Forster’s Terns may be most easily seen standing or walking along the shore or on the beach, where their pale wing tips and (in summer) black-tipped orange bill may be most apparent. With the aid of binoculars, it may also be possible to observe this species feeding by diving headfirst into the water. Forster’s Terns are most active during the day.

Threat Status: Least concern

Forster's terns, Sterna_forsteri breed in North America. They are most common in south-central Manitoba, northern California, southern Oregon and along the Gulf Coast. They winter along the Pacific Coast in California, on the Atlantic Coast of the United States (south of New Jersey), in Mexico, the Bahamas, Guatemala, the Greater Antilles and on the coast of the Gulf of Mexico.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

N America; winters s US to Costa Rica and Greater Antilles.

Gulf of Maine, Gulf of Mexico, Irish Exclusive economic Zone, North America, North West Atlantic, Portuguese Exclusive Economic Zone, Spanish Exclusive Economic Zone, United Kingdom Exclusive Economic Zone

Gulf of Maine to the Gulf of Mexico

Forster's Tern can be found in North and Central America, breeding seasonally in southern Canada and northern USA, wintering in south-east and coastal south-western USA, along the eastern and western coast of Mexico and in Central America. It can also be found year-round on the Atlantic coast of the USA from Virginia to Texas¹.

Forster's terns, Sterna forsteri, winter in California, on the Atlantic Coast of the United States (south of New Jersey), in the Bahamas, Guatemala, the Greater Antilles and on the coast of the Gulf of Mexico. They breed in scattered patches throughout North America.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDS: central Prairie Provinces of Canada (Lake Winnipeg, Manitoba, to southeastern British Columbia) south to southern California, western Nevada, southern Idaho, northern Utah, northern and eastern Colorado, central Kansas, western Nebraska, northern Iowa, northwestern Indiana, to eastern Michigan; coastally from northeastern Mexico (Tamaulipas), southeastern Texas to southern Alabama; along the Atlantic coast from Long Island to (rarely) South Carolina. WINTERS: central California and Baja California to Oaxaca and Guatemala, casually to Costa Rica; northern Veracruz to western Florida; Virginia to northern Florida; Bahamas and Greater Antilles.

Forster's terns are medium-sized birds. They are mostly white, with a pale gray back and wings and a black cap. They have long tails that form a deep “V” shape, and their outer tail feathers are long, like streamers. Their legs are orange, and their bills are orange with a black tip.

In winter, Forster’s terns do not have a black cap. Instead, they have a black mark behind each eye. Male and female Forster’s terns look the same. They weigh 130 to 190 g, and are 33 to 36 cm long. Young Forster’s terns look like adults, but have darker wing feathers.

Range mass: 130 to 190 g.

Range length: 33 to 36 cm.

Sexual Dimorphism: sexes alike

Forster's terns are medium-sized birds. They are white with a pale gray back and wings and a black cap. They have very deeply forked tails with long, streamer-like outer-retrices. Their legs are orange, and their bills are orange with a black tip. In winter they lack the black cap, but have a distinctive black mark behind each eye. Male and female adults are similar in appearance. Adults weigh 130 to 190 g, and are 33 to 36 cm long. Immature birds are similar in appearance to adults, but generally have darker primaries.

Forster's terns that breed in western and interior North America appear slightly larger and having darker upperparts than those that breed along the Atlantic and Gulf coasts. These groups have been designated as subspecies of Forster's terns, Sterna forsteri forsteri and Sterna forsteri litoricola. However, the designation of these groups as subspecies is not universally accepted. some ornithologists consider Sterna forsteri to be monotypic.

Range mass: 130 to 190 g.

Range length: 33 to 36 cm.

Sexual Dimorphism: sexes alike

Length: 37 cm

Weight: 158 grams

Forster's terns are found in fresh, brackish, and saltwater marshes, including marshy borders along lakes, islands, and streams.

Habitat Regions: temperate ; terrestrial ; saltwater or marine ; freshwater

Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water

Wetlands: marsh

Other Habitat Features: estuarine

Habitat and Ecology

Systems

• Terrestrial
• Freshwater
• Marine

Forster's terns are found in fresh, brackish, and saltwater marshes, including marshy borders along lakes, islands, and streams.

Habitat Regions: temperate ; terrestrial ; saltwater or marine ; freshwater

Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water

Wetlands: marsh

Other Habitat Features: estuarine

Depth range based on 104 specimens in 1 taxon.
Water temperature and chemistry ranges based on 24 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 12.690 - 26.954
  Nitrate (umol/L): 0.212 - 3.533
  Salinity (PPS): 33.002 - 36.184
  Oxygen (ml/l): 4.688 - 6.278
  Phosphate (umol/l): 0.057 - 0.659
  Silicate (umol/l): 1.023 - 6.162

Graphical representation

Temperature range (°C): 12.690 - 26.954

Nitrate (umol/L): 0.212 - 3.533

Salinity (PPS): 33.002 - 36.184

Oxygen (ml/l): 4.688 - 6.278

Phosphate (umol/l): 0.057 - 0.659

Silicate (umol/l): 1.023 - 6.162
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Comments: Freshwater and salt marshes, in migration and winter also seacoasts, bays, estuaries, rivers and lakes (AOU 1983). Nests on inland lakes and marshes, or on salt marshes (especially on wrack) along the coast. Along the Gulf Coast, commonly nests on dredged material as well as on wrack in salt marshes. At San Francisco Bay, California, commonly nests on old dikes or dredged-material islets in salt evaporation ponds. Nests on floating mass of marsh plants, on muskrat house, or old grebe's nest, or in a depression lined with grasses and pieces of shells. Human-made nesting platforms made of bundles of PHRAGMITES or TYPHA on floating base of styrofoam and wood or tires were readily used for nesting in Wisconsin (see Spendelow and Patton 1988). See Spendelow and Patton (1988) for further information on freshwater nesting habitats. See Cuthbert and Louis (1993) for information on nesting habitat in Minnesota.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Migrates primarily through interior North America. Migratory status in the western Gulf of Mexico? Birds from Atlantic coast breeding population apparently disperse northward, at least to New England, prior to fall migration (AOU 1983).

Forster's terns eat small fish, arthropods and occasionally Anura. They hunt by flying back and forth above the water, searching for food. When they spot prey, they either dive directly into the water toward the prey or hover for a few seconds and then plunge head-first toward the water. Sometimes, Forster's terns hunt from perches, such as posts, bridges and telephone wires.

Animal Foods: amphibians; fish; insects

Forster's terns eat many species of small fish, arthropods and occasionally frogs.

Forster's terns hunt by flying back and forth over the water with their bill pointing downward and their feet folded against their body. They typically fly about 6 to 8 m above water. When they spot prey, they either plunge directly into the water toward the prey or hover briefly before diving. They occasionally hunt from perches, such as posts, bridges and telephone wires.

Animal Foods: amphibians; fish; insects

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)

Comments: Catches flying insects (e.g., dragonflies, caddisflies) or snatches up insects (e.g., dead beetles) off the surface of the water while in flight; dives into water for fishes (Terres 1980).

Forster's terns affect the populations of the animals they eat. They are also an important food source for their predators. Forster's terns provide habitat for many different parasites, including at least three species of Mallophaga.

Red-necked grebes (Podiceps_grisegena) and American coots (Fulica_americana) sometimes lay eggs in the nests of Forster's terns. If the terns care for these eggs, they help the grebe and coot populations.

Black-crowned night-herons (Nycticorax_nycticorax), herring gulls (Larus_argentatus), great horned owls (Bubo_virginianus), short-eared owls (Asio_flammeus), snapping turtles (Chelydra_serpentina), marsh rice rats (Oryzomys_palustris) and mink (genus Mustela) are all predators of Forster's terns.

Forster's terns are protected from some predators by their nest sites, which are often surrounded by water. When a predator does enter a colony, the terns dive and swoop at the predator, sometimes striking the predator on the back.

Known Predators:

• black-crowned night-herons (Nycticorax_nycticorax)
• herring gulls (Larus_argentatus)
• raccoons (Procyon_lotor)
• great horned owls (Bubo_virginianus)
• short-eared owls (Asio_flammeus)
• marsh rice rats (Oryzomys_palustris)
• minks (Mustela)
• snapping turtles (Chelydra_serpentina)

Forster's terns have an impact on populations of the prey they eat and are an important food source for their predators. Their nests are also occasionally parasitized by red-necked grebes (Podiceps grisegena) and American coots (Fulica americana). Forster's terns host several species of external parasites, including at least three species of lice.

Known predators of Forster's terns include black-crowned night-herons (Nycticorax nycticorax), herring gulls (Larus argentatus), great horned owls (Bubo virginianus), short-eared owls (Asio flammeus), snapping turtles (Chelydra serpentina), marsh rice rats (Oryzomys palustris) and mink (genus Mustela).

Floating nest sites and nests on muskrat lodges isolate and protect Forster's terns from some predators. Terns respond to predators that enter a colony by diving and swooping at them, sometimes striking the predator's back.

Known Predators:

• black-crowned night-herons (Nycticorax nycticorax)
• herring gulls (Larus argentatus)
• raccoons (Procyon lotor)
• great horned owls (Bubo virginianus)
• short-eared owls (Asio flammeus)
• marsh rice rats (Oryzomys palustris)
• minks (Mustela)
• snapping turtles (Chelydra serpentina)

Sterna forsteri (Gulls and Terns) preys on:
Pagurus
Pagurus maclaughlinae
Libinia dubia
Pinixia floridana
Neopanope texana
Callinectes sapidus
Processa bermudiensis
Penaeus duoarum
Palaemonetes floridanus
Anchoa mitchilli
Menidia beryllina
Laridae
Cyprinodon variegatus

Based on studies in:
USA: Florida (Estuarine)

This list may not be complete but is based on published studies.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

10,000 - 100,000 individuals

Comments: The 1982 breeding population from New York to Virginia was estimated at 4600 birds. Most of the Gulf Coast breeding population (about 23,000) occurs in Louisiana. About 8000 birds nested along the Pacific coast in the late 1970s, mostly in the San Francisco Bay area.

Breeding: Forage up to 3.2 kilometers from nest (Van Rossem 1933). Nonbreeding: singly or in small loose groups.

Forster's terns use calls and visual displays to communicate.

Communication Channels: visual ; acoustic

Forster's terns use calls and visual displays to communicate.

Communication Channels: visual ; acoustic

Young are semi-precocial at birth. Their eyes are open, down is present, and they are able to walk upon hatching. Although they can walk, they are nidiculous (stay in the nest). (Nice 1962) Egg-teeth are lost within 3-5 days of hatching. Young are known to leave the nest as early as 4 days, but are not capable of flight until 4 or 5 weeks. (Hall 1988, 1989)

Young are semi-precocial at birth. Their eyes are open, down is present, and they are able to walk upon hatching. Although they can walk, they are nidiculous (stay in the nest). (Nice 1962) Egg-teeth are lost within 3-5 days of hatching. Young are known to leave the nest as early as 4 days, but are not capable of flight until 4 or 5 weeks. (Hall 1988, 1989)

Not much is known about the lifespan of Forster's terns. The oldest banded Forster's tern on record was 12 years old when it died.

Range lifespan
Status: wild: 12 (high) years.

Average lifespan
Status: wild: 190 months.

Not much is known about the lifespan of Forster's terns. The oldest banded Forster's tern on record was 12 years old when it died.

Range lifespan
Status: wild: 12 (high) years.

Average lifespan
Status: wild: 190 months.

Maximum longevity: 12 years (wild)

Forster's terns breed in colonies. They are monogamous. Males and females look for mates around the time that they arrive on the breeding grounds in the spring. Males try to attract a female by performing displays, and bringing food (fish) to the female. This is called courtship feeding.

Mating System: monogamous

Forster's terns breed in April and May. The female lays 2 or 3 eggs that are buff-colored and spotted. The nest is made of dead plant material, and is built on the shoreline, or on top of a muskrat lodge or a floating mat of plants. The parents take turns incubating the eggs for 20 to 28 days. When the chicks hatch, they can walk, but they still depend on the parents to feed them. The parents brood the chicks for about 3 days, and feed the chicks for at least 4 weeks. The chicks can fly when they are 4 to 5 weeks old. They probably do not begin breeding until they are at least 2 years old.

Breeding interval: Forster's terns breed once per year.

Breeding season: April and May

Range eggs per season: 1 to 6.

Average eggs per season: 3.

Range time to hatching: 20 to 28 days.

Range age at sexual or reproductive maturity (female): 2 (low) years.

Range age at sexual or reproductive maturity (male): 2 (low) years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Average eggs per season: 3.

Both parents incubate the eggs and brood the chicks for at least three days after they hatch. After the chicks hatch, both parents feed them until they are able to fly.

Parental Investment: no parental involvement; precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female); pre-independence (Provisioning: Male, Female)

Forster's terns breed in colonies, and are monogamous. Pair formation appears to occur around the time arrival on the breeding grounds in April. Courtship includes a number of displays and postures, including courtship feeding.

Mating System: monogamous

Forster's terns breed in April and May. The female lays 1 to 6 (usually 2 or 3) buff, spotted eggs on a nest dead vegetation. The nest is built on marshy shoreline, on top of a muskrat lodge, or on a mat of floating vegetation. The male and female both participate in incubation, which lasts 20 to 28 days. The chicks are semi-precocial when they hatch; they have open eyes, down, and are able to walk but remain in the nest and are fed by adults. The chicks are brooded by both adults for the first 3 days or so, and are fed for at least 4 weeks. They are able to fly 4 to 5 weeks after hatching. The age of first breeding is unknown, but is believed to be at least 2 years.

Forster's terns breed in April and May. The female lays 2 or 3 eggs that are buff-colored and spotted. The nest is made of dead plant material, and is built on the shoreline, or on top of a muskrat lodge or a floating mat of plants. The parents take turns incubating the eggs for 20 to 28 days. When the chicks hatch, they can walk, but they still depend on the parents to feed them. The parents brood the chicks for about 3 days, and feed the chicks for at least 4 weeks. The chicks can fly when they are 4 to 5 weeks old. They probably do not begin breeding until they are at least 2 years old.

Breeding interval: Forster's terns breed once per year.

Breeding season: April and May

Range eggs per season: 1 to 6.

Average eggs per season: 3.

Range time to hatching: 20 to 28 days.

Range age at sexual or reproductive maturity (female): 2 (low) years.

Range age at sexual or reproductive maturity (male): 2 (low) years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)

Average eggs per season: 3.

Brooding behavior is poorly documented in Forster's terns, but adults appear to brood young less than 3 days old and during stormy periods. Both adults feed young at least until they are able to fly, and most likely longer.

Parental Investment: no parental involvement; precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female); pre-independence (Provisioning: Male, Female)

Along the U.S. mid-Atlantic coast, lays eggs from late May to mid-June. Both sexes incubate usually 3-4 eggs for about 23-24 days. Semi-precocial young are tended by both adults until capable of flight, fledge at 3-4 weeks, remain with parents well into the fall (Byrd and Johnston 1991). Often renests if first nest is lost to tidal flooding. Nests in loose colonies or singly. Colony size along the Atlantic coast is less than 500, up to several thousand in Louisiana (Spendelow and Patton 1988).

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 2 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 4
Species With Barcodes: 1

Canada

Rounded National Status Rank: N4B - Apparently Secure

United States

Rounded National Status Rank: N5B,N5N : N5B: Secure - Breeding, N5N: Secure - Nonbreeding

Forster's terns are protected by the federal government under the US Migratory Bird Treaty Act. They are also designated as a "species of special concern" in Michigan and Minnesota and are "endangered" in Illinois and Wisconsin.

There are about 120,000 Forster's terns in the world. Most deaths in this species are probably due to predation and eggs that are lost during storms, heavy rains and high waves.

IUCN Red List of Threatened Species: least concern

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: special concern

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 2008
  Least Concern
• 2004
  Least Concern

Forster's terns are not protected under the Endangered Species Act or CITES. However, they are designated as a species of special concern in Michigan and Minnesota and are endangered in Illinois and Wisconsin. They are also protected under the US Migratory Bird Treaty Act.

There are an estimated 120,000 Forster's terns worldwide. The most important causes of mortality in this species are probably predation and egg loss due to storms, heavy rains and high waves.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: special concern

IUCN Red List of Threatened Species: least concern

Rounded Global Status Rank: G5 - Secure

Comments: Threats include human disturbance and development of nesting areas, loss of nests to natural flooding, and possibly predation by laughing gulls (Byrd and Johnston 1991).

There are no known adverse affects of Forster's terns on humans.

We do not know if this species affects humans.

There are no known adverse affects of Forster's terns on humans.

We do not have information on the economic importance of this species for humans.