diagnostics

47-54 cm; c. 690 g. The largest tern; more reminiscent of a gull in terms of size and the massive red bill. Cap black. Nape, scapulars and back pale grey. Rump and tail white. Upperwing pale grey with white trailing edge, depending on wear and moult. Underwing white with diagnostic blackish grey outer primaries. Underparts white. Bill red with pale tip and black sub-terminal band. Eyes reddish brown. Feet and legs black with orange or pink soles. Sexes alike, but female slightly smaller. Non-breeding adult shows white streaks on crown. Juvenile has paler, more orange-toned bill and greyish yellow to dark orange legs. Feathers of mantle, scapulars and some wing coverts with scaled pattern. Lacks dark carpal characteristic of many young terns (Tree 2005).

trophic

The species breeds colonially, with the season varying between localities (Crawford 1997). The number of colonies used for breeding and the numbers of birds present at each varies widely between years (Crawford 1997). Breeding habitat used along the coast is largely offshore islands with an increasing use of sandy beaches and islands at salt works, where protection is offered (du Toit et al. 2003). Breeding at inland sites takes place on small, low islets in pans and dams. Caspian Terns are intolerant of any form of disturbance while breeding. A generation length of 12.2 years is provided by BirdLife International (2014).

Hunting is carried out 3-20 m above the water, parallel to, and within 100 m of the shoreline. Birds dive head first into water when catching prey (Cyrus and McLean 1994) and feed throughout the day with most activity during the morning. Their diet consists almost entirely of fish of 5-20 cm in length and weighing 10-20 g.