Black Tern (Chlidonias niger)

[order] Charadriiformes | [family] Sternidae | [latin] Chlidonias niger | [UK] Black Tern | [FR] Guifette noire | [DE] Trauerseeschwalbe | [ES] Gaviotin Negro | [IT] Mignattino | [NL] Zwarte Stern

Subspecies

Physical charateristics

The black tern has a holarctic distribution with two subspecies: C. niger niger (European black tern) and C. niger surinamensis (North American black tern). The black tern is a small dark tern, with blackish head, neck, and underparts (blacker in male than female), and greyish back, wings, and tail (whitish undertail coverts) in alternate (i.e., breeding season) plumage. The bill is black, eyes are dark, and legs are dark reddish brown. In late summer and fall, underparts are blotched black and white during pre-basic molt. In basic plumage, the head, neck and underparts are white, and the upperparts are smoky grey. The juvenile bird has a white face, foreneck, breast and belly with an irregular black cap connected to a dark ear spot.

Listen to the sound of Black Tern

[audio:http://www.aviflevoland.nl/sounddb/B/Black Tern.mp3]

Copyright remark: Most sounds derived from xeno-canto

Range

In North America, black terns occur across most of southern Canada and the northern United States. They breed in all provinces of Canada except Prince Edward Island and Newfoundland. However, they are most common from central British Columbia across the prairie provinces to central Ontario and southern Quebec. In the northern United States, black terns breed south to central California, northern Utah, Wyoming, Kansas, Iowa, Illinois, Indiana and Ohio to central and northern New York and northern New England. In Michigan, this species occurs mainly along the Great Lakes shorelines, but are also found at some inland locations. Black terns usually migrate along the Atlantic coastline and mainly winter in marine and coastal areas south of the Gulf Coast through Central America to northern South America. In Suriname the black tern is a scarce migrant found in lagoons mostly in small flocks.

Habitat

Black tern colonies occur in freshwater marshes and wetlands with emergent vegetation found along lake margins and occasionally in rivers. Vegetation can vary greatly, but cattails or bulrushes are characteristically dominant in black tern colonies. Vegetative cover varies between dense and sparse but nests are usually protected from direct open water to avoid dangers such as wind and wave action. Overall, black terns tend to nest at sites with a 50:50 vegetation cover:open water ratio. However, suitable marsh habitat of 5 ha or more is thought to be necessary. Nests are largely composed of the previous
seasons vegetation, found near the building site. In many instances nests are depressions in floating matted vegetation, found on logs or boards, and occupying abandoned muskrat lodges. Nesting occurs in water depths ranging from 0.5 m to 1.2 m. Spatial separation between nests can vary between 3 m to 30 m. This semi-social distribution is unusual for tern species and black terns are often labeled as a loosely colonial breeding bird.
This species winters mainly in marine and marine-coastal areas in the Americas along the Pacific Coast from southern Mexico east and south to Peru and on the Atlantic coast from eastern Panama east along northern South America to French Guiana

Reproduction

One to five eggs may be laid, although the normal clutch is usually two or three. Clutches with four eggs have been reported in only two recent studies and are apparently quite rare. Single egg clutches may often be replacement nests or nests where one or more eggs have already been lost. Incubation begins with the laying of the first egg, and eggs require 20-24 days to hatch.

Young are tended by both parents. Chicks are able to swim, walk and run by the time they are two days old. The chicks grow rapidly, doubling their weight in less than three days and quadrupling their weight in less than six days. The rate of weight gain slows after the eighth day. In some cases, chicks may be relocated from the nest site to “auxiliary” nests within a few days after hatching. If disturbance at the nest is minimal, young may remain at the original nest site for as long as 14-25 days, although they hide in the vegetation at the sign of danger and may be found swimming as far as 15 meter from the nest. The majority of chicks are flying at 21 days.

Feeding habits

Black terns are primarily insectivorous on the breeding grounds where they capture insects at or near the water surface, but fish comprise a large part of the diet in some habitats. Both parents feed chicks and primary summer insect foods include damselflies and dragonflies, but also mayflies, caddisflies, beetles, moths, dipterans, grasshoppers, crickets, amphipods and others. Black terns also feed opportunistically on small fish (2 to 3 cm in length) in summer where available, but many palustrine wetlands have none. Food habits are related to breeding biology in that a male black tern will carry a small fish (or large insect) in his mouth while aerially displaying to a female during pair bond formation (commonly called a ?fish flight?. During migration, black terns may concentrate on swarming insects, but dietary composition (frequency of insects versus fish) varies widely. In winter, black terns in marine environments are largely piscivorous, foraging on small fish that are driven to the surface by predators. In European black terns, fish may dominate the diet by mass and provide an important source of calcium.

Conservation

This species has a large range, with an estimated global extent of occurrence of 10,000,000 km². It has a large global population estimated to be 450,000¿1,300,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern.

Migration

During migration, black terns are present throughout the interior of North America south of the breeding range, along both coasts and the interior of Middle America, along the Atlantic coast from Nova Scotia south to Florida, the West Indies, and Trinidad, and in northern South America east to French Guiana and south to Ecuador and Peru, and often far out at sea. The species is casual to accidental in the Hawaiian Islands, Alaska, Newfoundland, Prince Edward Island, Clipperton Island, Bermuda, Chile, Brazil, Uruguay, and northern Argentina. Movements during winter are poorly understood and important wintering locations are not well documented. Generally, in winter black terns are found in marine waters, mostly within <30 km of land. They are also found in coastal areas and productive freshwater lakes, usually near coastlines.

Distribution map

Literature

Title Black Tern (Chlidonias niger surinamensis):
A Technical Conservation Assessment

Author(s): David E. Naugle

Abstract: The black tern (Chlidonias niger surinamensis) sti..[more]..

Source: Wildlife Biology Program, School of Forestry