Great crested tern: where and when to see them

The great crested tern is a large coastal tern with pale gray upperparts, white underparts and a long yellow bill. Its shaggy black crest gives resting adults a distinctive swept-back appearance. Distributed around much of the tropical and subtropical Indian and western Pacific oceans, it favors marine coasts rather than inland wetlands. In Southeast Asia, local presence depends on island habitat, seasonal movements and the availability of small fish.

Size

43-48 cm long

Weight

300-450 g

Lifespan

Not reliably established

Status

Least Concern

Great crested terns patrol coastal waters with elastic wingbeats, scanning downward before dropping sharply to seize fish. They often rest together on sand spits, rocks or quiet beaches, sometimes mixing with other terns. Breeding occurs in dense ground colonies, where neighbors defend small spaces around their eggs. Adults carry fish crosswise in the bill, and food presentation plays a role in courtship as well as feeding dependent young. Courtship displays often involve aerial chases and fish presentations, with the male offering fish to the female. They are colonial breeders, sometimes forming mixed colonies with other tern species, and their nests are simple scrapes on the ground, often with minimal lining.

• Its black crest becomes more ragged-looking when raised.
• Most pairs lay a single egg.
• The forehead becomes noticeably whiter outside breeding condition.
• Adults can recognize their chicks within crowded colonies.

For Thailand's Andaman coast, November through April generally offers easier shore travel. Vietnam requires coast-specific planning because monsoon patterns differ substantially. These are practical travel considerations, not a single breeding calendar, and local tern numbers can fluctuate independently of fair weather. The Great Crested Tern is a resident breeder across much of its Southeast Asian range, although local populations may undertake short migratory movements or dispersal. Nesting generally occurs during the dry season or early monsoon, with exact timing varying by latitude and local conditions.

The species uses shallow coastal seas, reef-fringed islands, estuaries and sandy bays. Bare sand, shell banks and low rocky islands can support colonies or roosts. Suitable shore viewpoints overlook open feeding water without requiring entry onto sensitive nesting or resting sites. They are highly adaptable to human presence and are frequently seen in harbors, near fishing villages, and even around aquaculture operations. These terns are rarely found far from the coast, typically remaining within 20 kilometers of the shore.

Small fish are the principal food, especially schooling species captured close to the surface. Squid, crustaceans and occasional other marine animals supplement the diet. Birds may exploit fish driven upward by larger predators or take suitable scraps around fishing activity. Foraging is typically done by plunge-diving from heights of 5 to 15 meters, often targeting shoals of fish visible from above. While they primarily hunt live prey, they are opportunistic and may scavenge discards from fishing boats, especially in busy marine areas.

Common name

Great crested tern

Scientific name

Thalasseus bergii

Animal group

Birds

Size

43-48 cm long

Weight

300-450 g

Lifespan

Not reliably established

Status

Least Concern

Identification

Compared with the lesser crested tern, it is larger and heavier-billed, with a yellow rather than usually orange bill and generally darker gray upperparts. Juveniles are distinguishable by their mottled brown upperparts, dark bill, and less defined black crest, which gradually develops over their first year. In flight, their long, narrow wings and typical tern shape, coupled with their size, help differentiate them from smaller tern species.