The Caspian Tern is found in salt and fresh water around the entire Australian coast as well as inland over the eastern half of the continent and in Tasmania. As well as more sheltered coastal waters this bird is found on beaches, mudflats, estuaries, larger rivers, reservoirs and lakes. In flight uses powerful, regular wingbeats while patrolling the surf line and inshore waters at heights between 10 and 20 metres. The bill typically points down. Eats mainly fish up to 18 centimetres long. When prey is seen the bird turns, folds it wings and plunges into the water, sometimes it hovers briefly before diving.
Common but scattered and not concentrated. Usually solitary or in pairs; some adults may be sedentary on prime feeding territory while other adults, and immature birds, seem to be nomadic.
Breeds from September to December in the south, any time in the north. Single nests or small colonies. The nest is a bare scrape on the ground. One or two eggs are laid; matt stone-grey or light brown in colour; blotched sparingly grey-brown and black; long-oval, about 65 by 45 millimetres. Incubated for 20 to 22 days by both parents. Chicks are brooded in the nest for a few days before being led off to cover under low vegetation. When defending the nest or chicks the parents pive a skim past intruders screaming as they fly.
Widespread globally; found in Eurasia, Africa, North America and New Zealand. One race found in Australia.
¶ Genus Hydroprogne is in Family Laridae containing the Gulls, Terns and Noddies. There is considerable scientific debate over whether the Caspian Tern should be included in genus Sterna with many other terns or should be separated as Hydroprogne; different sources have taken different approaches at different times so the species may be listed as Hydroprogne caspia or as Sterna caspia. Opinion presently favours the former name.