The Caspian Tern (Hydroprogne caspia) is the world's largest tern — a massive bird about the size of a Herring Gull, with a heavy, blood-red bill visible at long range. It measures 48–60 cm with a wingspan of 130–145 cm and weighs 530–780 g. Its most striking feature is the massive, bright red bill with a dark tip, unlike any other tern in the region. The crown is black in breeding plumage, becoming a streaked greyish-black cap in winter; the upperparts are pale pearl-grey, the underparts white, and dark tips show on the underside of the primaries in flight. The tail is only shallowly forked, adding to the gull-like impression, and the heavy, gull-like flight combined with harsh, barking calls make the species distinctive.
The call is a hoarse, rasping, powerful "kraah" or "kräh-kräh", deeper and coarser than the lighter cries of smaller terns and often heard before the bird is seen. In Sweden the species breeds mainly in the outer Baltic archipelagos, with concentrations around Stockholm and Uppland as well as the coasts of Öland, Gotland and Blekinge; the Swedish population is estimated at 500–800 pairs. It nests in colonies or small groups on open gravel or rocky islets in the outer archipelago, typically free of ground predators, with the female laying 2–3 eggs in a simple scrape — the species is highly sensitive to disturbance and colonies can be abandoned entirely if people, dogs or White-tailed Eagles intrude. The diet is almost exclusively fish, hunted by flying at 10–15 m and plunge-diving straight into the water for species such as roach and perch. It is classified as Vulnerable (VU) in Sweden, reflecting its few colonies, high sensitivity to disturbance, and dependence on Baltic Sea food supplies.
Read about this species in Swedish →