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Black Tern (Chlidonias niger)

The Black Tern is the commonest of the three dark-plumaged terns collectively known as Marsh Terns. These differ from the other terns, Sea Terns, in typically breeding inland, and in placing their nests on floating vegetation instead of on islands, beaches and sand-dunes. The Black Tern is less restricted in habitat than the other two, the White-winged Black Tern and Whiskered Tern, in that it may use both freshwater and brackish marshes, and it also ranges over a broader climatic range. Although it normally follows the Marsh Tern code by building its nest on floating vegetation in 50 cm or more of water, it will also sometimes use much shallower sites, and might even place its heap of weeds on the ground.

The feeding of Marsh Terns is quite different from that of Sea Terns. For one thing, the main diet in the breeding season is almost invariably insects with, in this species at least, small fish accounting for no more than 20% of the total food caught. The method of catching is also different, the Marsh Terns rarely plunging into the water, but instead dipping down elegantly and snatching food from the surface or just above it. The appearance of this foraging is distinctly leisurely and effortless, with lots of rising and falling, and lacking the earnest and purposeful style of Sea Terns. Marsh Terns also hawk in mid-air for flying insects, looking rather like outsize Swallows.

Black Terns nest in colonies. On arrival on the breeding grounds in April the birds typically scout around for a couple of weeks to check for suitable conditions. Then, once they have selected the site they act as nervously as a shy teenager asking for a date, landing on it only for a short time each day before bashfully flying off. Only a few days before first egg laying do they finally occupy the site, and then rapidly build their nests. Black Terns pair up in a similar way to Sea Terns, with “High Flying” forming a major component of courtship, often with as many as 20 birds taking part.

After breeding virtually the whole population of Northern and Eastern Europe gathers to moult and prepare for migration in just one place, the IJsselmeer in the northern Netherlands. Between 150,000 and 200,000 birds spend 2-3 weeks here in July and August, before resuming their journey.

In complete contrast to the other Marsh Terns, the Black Tern rather changes its spots in the winter and assumes the mantle of a marine tern. Its winter distribution is entirely coastal and it feeds almost entirely by dipping to the surface of the sea for small fish.