Common Tern (Sterna hirundo)

The common ternís low, piercing kee-ar-r-r-r and raspy tr-tee-ar calls form a surprising contrast to its graceful, acrobatic flight over the water as it searches for fish.

Description

The common tern is similar in shape to other terns, with a slim, streamlined body, arched wings, a forked tail and a spearlike bill. Its body and the rear half of its underwings are white, while the rest of its wings and its back are pale grey, except for a dark area under the wingtips. It has a jet black cap, red legs and a bright red bill with a dark tip. This tern is about 33-40 cm in length, a little larger than a blue jay. In the winter, its legs and bill become dark red or black and its black cap is confined to the back of its head, while its forehead becomes white. Juvenile terns have dark areas on top of their wings.

Distribution

The common tern breeds across Canada from Alberta east to Newfoundland, and north to the southern Northwest Territories. It nests on sandy shores throughout the Atlantic provinces. This species winters from Mexico south to Argentina.

Ecology

The common tern is monogamous and nests in large colonies, with each pair defending a small area around their nest. Typical colony sites are located on islands or beaches with sparse vegetation. The male tern courts a mate by bringing her food and performing strutting displays, which may be interrupted by male rivals, also bearing gifts of food. The nest consists of a simple scrape in the ground, lined with grass, seaweed, algae, or shells. Three buffy, olive, or brown, dark brown spotted eggs are laid, and are incubated by both sexes for three to four weeks. The third egg is typically smaller than the first two, and is the least likely to survive. The young are cared for by both parents for about 27 days. Occasionally, a pair of terns may attempt to raise a second brood in a season, but these broods are not commonly successful. When a predator enters a colony, adults take to the air and aggressively swoop down on the intruder. Often, the tern bombs the predator with droppings to drive it away. Be aware of this if you enter a tern colony - wear old clothes!

The common tern's diet is 90% fish, but also includes a few crustaceans and insects. It feeds by hovering high over the water and then diving to catch fish swimming near the surface. Young birds are fed regurgitated food until they are old enough to forage on their own. Feeding territories away from the colony are strictly defended during the nesting season, mostly by the male, and especially before incubation begins. This ensures that the female has plenty of resources with which to produce healthy eggs.

The hat-making trade of the 1900s decimated many tern colonies, which led to its being placed on the list of species of Special Concern. On the Great Lakes in particular, rising water levels and competition for nest sites with ever-growing populations of ring-billed gulls have also led to the reduction of itsbreeding populations.