Bird of the Month: Black Tern
By Andy McCormick
PC: Mick Thompson (Black Tern)
Scientific Name: Chlidonias niger
Length 9.75 in
Wingspan 24 in
Weight 2.2 oz
AOU Band code BLTE
The Black Tern is an attractive bird which has been described with enthusiastic language. It is especially striking in its breeding plumage of black head and smoky-gray body. The undersides of the wings are paler- “silver-gray –and it is this flash of silver that catches the eye when distant birds bank and wheel” (Dunne). Bent describes the Black Tern as, “a restless waif of the air, flitting about hither and thither with a wayward, desultory flight, light and buoyant as a butterfly.”
Black Terns patrol a marsh or lake catching insects in the air as a swallow would or flycatching insects around reeds and cattails. They will also drop down to the water to pick insects from the surface, but do not plunge dive as other terns will. In addition to insects their diet consists of small fish, tadpoles, crustaceans, earthworms and leeches. In winter they eat mostly fish (Kaufman).
The Black Tern shares the genus Chlidonias, a misspelling of the Greek khelidon, a swallow, with the White-winged Tern (C. leucopterus). The correct spelling would be Chelidonias, but the principle of priority in naming in the Linnaean system allows the error to continue (Holloway). Niger is Latin for black, a reference to the bird’s plumage. Tern is from the Old Norse taerne, their name for this type of bird.
These terns migrate overland in spring usually arriving in Washington in mid-May. They nest in fresh water marshes and construct a nest very close to the water on floating plant material or on an old muskrat nest. They may also nest in a depression lined with some vegetation. Usually 2-4 pale buff to olive-colored eggs are deposited. Incubation is shared by the parents and lasts about three weeks. The chicks develop quickly and leave the nest in 2-3 days and first flight occurs in about another three weeks.
Fall migration begins in late July with most birds migrating overland through the United States. Large flocks of thousands of Black Terns will mass at the Salton Sea and along the Gulf Coast. West coast birds will continue migrating southward which takes them out over the Pacific Ocean where they spend the winter months off the northwest coast of South America as a coastal seabird species. They winter in salt water but breed in fresh water.
The North American population of Black Terns in 1990 was one-third of what it was in 1960 (Alderfer). Many factors contribute to this reduction. The birds take two years to mature and will not breed until their second summer. This slows the rate at which new birds can replace those that die. Black Terns also nest very close to water and the nests are often wet and can be adversely affected by wind and water levels. The vulnerable position of nests also leaves them open to predation and subsequent chick loss. However, the greatest threat to the Black Tern has been the loss of wetland habitat. Estimates of the North American population of Black Terns are speculative and range from 100,000 to 500,000 (Heath, et al).