Black tern (Chlidonias niger)
|Size||Length: 23 - 28 cm (2)|
Wingspan: 57 - 65 cm (2)
|Weight||50 - 74 g (2) (3)|
Classified as Least Concern (LC) on the IUCN Red List (1).
A small, graceful tern species (4), the black tern is unmistakable during the breeding season, when it displays the distinctive dark plumage for which it is named. The head, neck and underparts are black, with slate-grey upperparts and wings, a grey tail and grey undersides to the wings. The undertail is white, the beak is black and the legs are short and blackish-red (2) (3). The male and female black tern are similar in appearance, but the female is slightly greyer. Outside of the breeding season, the black tern is markedly different in appearance, being pale grey above and white below, with a white head and with the black plumage restricted to a dark patch either side of the breast, a dark crown which joins a dark patch behind the eye, and a dark spot in front of the eye (2) (3). Juveniles resemble the non-breeding adults, but have a pale brownish wash on the forehead, a greyish-brown back and pale edges to the feathers, which give a scaly appearance (2) (3). The calls of this species include a short kip or kik (3).
Two subspecies of black tern are recognised: Chlidonias niger surinamensis is smaller and darker than Chlidonias niger niger, and outside of the breeding season has pale streaks on the crown and a wider dark patch on each side of the breast (2) (3).
Subspecies C. n. niger is found in Europe, from southern Scandinavia to southern Spain, and eastwards through Asia, as far as central Mongolia. A migratory species, it winters mainly on the west coast of Africa, as far south as South Africa. C. n. surinamensis occurs in the Americas, breeding in Canada and the northern United States, and wintering in Central America and northern South America (2) (3) (5).
The black tern occupies very different habitats during the breeding and non-breeding seasons. During the breeding season, it is a bird of freshwater and brackish wetlands, breeding on well-vegetated inland pools, lakes, marshes, ditches, peat bogs, swampy meadows, quiet stretches of rivers and in rice fields (2) (3) (4) (5). It shows a preference for areas with sparse, open vegetation such as sedges, reeds, cattails (Typha species) or floating water lilies, usually where the water is one to two metres deep (2) (5).
In contrast, the black tern uses coastal habitats in winter, including estuaries, salt marshes, bays and coastal lagoons (2) (3) (4) (5), and will even feed up to 600 kilometres offshore (5). During migration, this species uses both inland wetlands and more coastal habitats (2) (3) (4) (5).
The black tern is agile in the air and has a rather light, erratic-looking flight. While foraging, it typically circles low over land or water with relatively slow, shallow wing beats, and often feeds in flocks, particularly where food is concentrated (3). The black tern feeds predominantly on insects during the breeding season, although it also takes small fish, snails, amphibians, worms and crustaceans. Outside of the breeding season, the diet consists mainly of small marine fish (2) (3) (4) (5). Hunting takes place in flight, the tern either dipping to the water’s surface or the ground to pick up food items, or pursuing insects in the air. This species only rarely dives into water to catch prey (2) (3) (4). Black tern flocks often concentrate in areas where predatory fish or dolphins have driven prey to the water’s surface (2) (3) (5).
The black tern breeds in small colonies, often close to other species, between May and June (2) (3) (5). This species usually nests over shallow water, building a low mound of plant material on top of the water or on a floating mat of vegetation. A shallow scrape on the ground, an old muskrat (Ondatra zibethicus) house, or the old nest of another waterbird may also be used (2) (3) (4) (5). The nest is often flimsy and easily destroyed by wind or by changing water levels (3). Two to three eggs are laid (2), or sometimes up to six, and the eggshells are specially adapted to survive the damp conditions in the nest (3). Both the male and female incubate the eggs, which hatch after around 19 to 23 days (2) (3). The young terns develop rapidly and may leave the nest after just two to three days, although they remain in vegetation nearby (4). The young are able to fly after around 20 to 25 days (2) (3) (4), after which the family moves to an open area of water and defends a feeding territory. The adults continue to feed the young for two weeks or more (3) (4). The black tern leaves for its wintering grounds from July onwards (5), and young birds do not usually return to breed until at least the second year of life (3). The black tern may live for up to 17 years in the wild (2) (3).
The black tern is a widespread species with a large population, and is not currently considered at risk of extinction (5). However, many local populations are declining due to a range of threats, including the loss of wetland habitats to drainage and agriculture, habitat degradation due to the overgrowth of cattails (Typha species), human disturbance, and a reduction in prey as a result of pollution, pesticides, lake acidification and the introduction of exotic fish species (2) (3) (4) (5). Overfishing in its winter range may also affect this species by reducing prey availability (3), and outbreaks of avian influenza are a potential threat (4) (5). In parts of Europe, black tern numbers have decreased significantly during the last century, partly due to a reduced diversity of prey as a result of water eutrophication, leading to malnutrition or starvation in tern chicks (6) (7). Surveys in North America have also shown a decline in the black tern in recent decades, although this trend reversed somewhat during the 1990s (3) (8).
The black tern is listed on Appendix II of the Convention on Migratory Species (CMS), which aims to conserve migratory species throughout their range (9), and is also covered under the African-Eurasian Waterbird Agreement (AEWA), which aims to protect birds that are dependent on wetlands for at least part of their annual cycle (10). A range of conservation actions have already benefitted this species, including the provision of artificial nesting rafts and the use of herbicides to prevent the overgrowth of cattails in its breeding habitats (3) (5) (7) (11) (12). As the black tern readily moves to new nesting sites due to the ever-changing nature of its wetland habitats, it is also quick to accept artificial wetlands, such as cultivated rice fields and wetlands managed for waterfowl, as well as restored areas of habitat (3).
Conservation efforts for this species are now focusing on the protection of wetland habitats, minimising human disturbance at nesting colonies, and managing wetlands in ways that maintain suitable conditions for breeding terns (3) (5) (7) (11) (13). Further population surveys, as well as research into its breeding biology and its ecology at its wintering grounds, would also help inform conservation efforts for this beautiful small tern (3).
To find out more about the black tern and its conservation, see:
Birds of North America Online:
The Cornell Lab of Ornithology:
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- Avian influenza: also known as “bird flu”, a contagious disease caused by any strain of influenza virus that is carried by and primarily affects birds.
- Brackish: slightly salty water, usually a mixture of salt and freshwater, such as that found in estuaries.
- Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
- Eutrophication: a process in which a water body is enriched with excessive nutrients (such as nitrogen and phosphorus) resulting in the excessive growth of aquatic plants and the depletion of oxygen, creating unfavourable conditions for other organisms, such as fish.
- Incubate: to keep eggs warm so that development is possible.
- Subspecies: a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
- Territory: an area occupied and defended by an animal, a pair of animals or a colony.
IUCN Red List (September, 2010)
- del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
Heath, S.R., Dunn, E.H. and Agro, D.J. (2009) Black tern (Chlidonias niger). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
- Kaufman, K. (2001) Lives of North American Birds. Houghton Mifflin Harcourt, Boston, Massachusetts.
BirdLife International (September, 2010)
- Beintema, A.J. (1997) European black terns (Chlidonias niger) in trouble: examples of dietary problems. Colonial Waterbirds, 20(3): 558-565.
- Van der Winden, J. (2005) Black tern Chlidonias niger conservation in The Netherlands - a review. Vogelwelt, 126: 187-193.
- Peterjohn, B.G. and Sauer, J.R. (1997) Population trends of black terns from the North American Breeding Bird Survey, 1966-1996. Colonial Waterbirds, 20(3): 566-573.
Convention on the Conservation of Migratory Species of Wild Animals (September, 2010)
Agreement on the Conservation of African-Eurasian Migratory Waterbirds (September, 2010)
- Linz, G.M., Bergman, D.L., Blixt, D.C. and Bleier, W.J. (1994) Response of black terns (Chlidonias niger) to glyphosate-induced habitat alterations on wetlands. Colonial Waterbirds, 17(2): 160-167.
- Shealer, D.A., Buzzell, J.M. and Heiar, J.P. (2006) Effect of floating nest platforms on the breeding performance of black terns. Journal of Field Ornithology, 77(2): 184-194.
- Hötker, H. and Van der Winden, J. (2005) Numbers, distribution and protection of black terns Chlidonias niger breeding in Germany 1990-2003 with comparisons to the Netherlands. Vogelwelt, 126(3): 179-186.