Saturday, 2 February 2013

Black Tern


order : Charadriiformes      Genus & Species : Sternidae     Family : Chlidonias niger

The black tern is 1 of 3 species in the genus Chlidonias. While its buoyant flight makes it look almost weightless, the feisty black tern makes a strong impression when it utters its prolonged, shrill scream to fend off intruders. With its short tail and wings, the black tern appears erratic and batlike in flight, often dipping to the water’s surface to pick up food with its bill. They found in Scandinavia, Europe, western Asia and Africa; also in North America, as well as Central and South America. 

Habitat : The black tern will live on virtually any wetland, including well-vegetated inland pools, lakes, peat bogs, rice fields, brackish marshes and even small ponds and ditches. The bird prefers sparse, open vegetation such as bulrush, cattail and, if available, floating water lilies. Foraging over wetlands, but also in drier areas, black terns can often be found roosting on branches of downed trees or on pilings. In the colder winter months, large groups of black terns inhabit estuaries, coasts and coastal lagoons. 
Food & Feeding : A low-flying predator that prefers to feed mainly in the daytime, the black tern feasts on aquatic insects, small fish, snails, tadpoles and frogs, which make up the bulk of its extremely varied diet. When foraging, black terns constantly dip over water to snatch aquatic prey from the surface, but very rarely plunge into the water completely. The opportunistic birds are often seen close to the shore, feeding on small fish that have been forced to the surface by a pod of feeding dolphins. Instead of flying, the tern sometimes hunts from a perch high over water. During the breeding season, the black tern prefers to feed insects to its nestlings. Tern favorites include dragonflies, moths, crickets and flies, which it captures by snatching them from the air. In fact, insects comprise over 90% of the food brought back to hungry nestlings. The tireless black tern zigzags back and forth after dragonflies in long pursuits that can last up to 10 seconds each. As it circles low over its various foraging areas with slow, shallow wingbeats and a downward- pointing bill, the gregarious black tern often congregates with other birds in large flocks where food is heavily concentrated. 
Behavior : Gregarious in nature, flocks of black terns may bathe together in extremely dense groups, also gathering in large flocks where there is a heavy concentration of food. During these interactions, the black tern’s call is a sharp klitt, or a short, nasal kja, which sounds quite clipped.The black tern is often mistaken for a bat or storm petrel, due to its erratic flight, frequent hovering and dark summer plumage. Although its feet are webbed, the black tern rarely settles on water when hovering in search of prey. Despite its fragile, almost meek appearance, the black tern is suprisingly agressive: intruders are met with a shrill scream, kreek or craik, and then quickly chased away. 
Breeding : From May to August, black terns practice what is known as assortative mating, by which bird pairs are formed by size. Most colonies contain fewer than 20 breeding pairs, and rarely more than 100. The female makes her nest in a shallow depression by assembling masses of floating vegetation or selecting clumps of dead reeds or cattail root stalks.These water-based nests are usually found floating in shallow freshwater or brackish marshes. In her floating nest, the female tern lays from 2–4 eggs, which are pale brown with darker brown blotches. Incubation lasts for about 21–22 days and, within two short hours after hatching, the hungry chicks are fed their first meal. After about 25 days of feeding and care, the hardy chicks are ready to leave the nest. 

Bill : The black tern plucks food from land, water or air with its sleek, black bill. 
Eyes : The tern’s keen vision allows it to snatch flying insects in midair. 
Plumage : It is the only tern with a black body, but the bird’s back and wings are gray. 
Tail : The short, notched tail is only slightly forked and when spread out in flight it acts as a rudder. 
Feet : Only the front digits are webbed, allowing the bird to swim and walk equally well. Strong claws enable the bird to perch easily. 
In Flight : The black tern hovers in the air on broad wings. 

Weight : 2–2.5 oz. 
Length : 8.5-9.5"
Wingspan : 22.5-25.5"
Sexual Maturity : 2-4 years
Breeding Season : May–August 

The tern will sometimes build its water-based nest on an already assembled muskrat home.