Caspian Tern: where and when to see them

The Caspian tern is the world's largest tern, a substantial waterbird with a massive red bill and a harsh, carrying voice. It occurs on several continents, using both coastal and inland waters. In Croatia it is principally a scarce passage visitor rather than a routine feature of every harbour. Its powerful proportions can initially suggest a gull, but its feeding flight and pointed wings reveal its tern identity.

Size

48-60 cm long; 127-145 cm wingspan

Weight

530-780 g

Lifespan

Not reliably established

Status

Least Concern

Caspian terns search for fish in deliberate flight, hovering briefly before dropping into the water. They rest on open sandbars, mudflats and exposed shores, sometimes alongside gulls and smaller terns. Breeding birds form colonies or nest in scattered pairs, defending the nest area vigorously. Parents continue feeding young after fledging, and family associations may persist during migration. Their loud, rasping calls often announce their arrival before the bird is noticed. Courtship displays often involve aerial chases and presentation of fish by the male to the female. While generally colonial, they can sometimes be found nesting solitarily or in very small groups, especially at the edges of their range.

• It is the sole living species in the genus Hydroprogne.
• Its wingspan can exceed that of many familiar gulls.
• Adults can carry fish crosswise in the bill to feed young.
• Despite its name, it has a near-global distribution rather than a solely Caspian range.

Spring and autumn migration offer the most plausible opportunities in Croatia, especially around larger coastal wetlands. April to May and August to October are useful broad search periods. Numbers fluctuate, and local reports are more informative than a fixed annual calendar. Early autumn, particularly September, can be excellent as large groups may gather prior to their southward journey. During spring migration, smaller numbers might pause along the Adriatic coast before moving to breeding grounds further north or east.

Suitable habitats include estuaries, lagoons, shallow coastal bays, large lakes and reservoirs. Open resting areas near fish-rich water are important. Breeding sites typically have sparsely vegetated sand, gravel or shell, while migrants use a broader selection of quiet wetland margins. The species also frequently utilizes artificial habitats such as salt pans and aquaculture ponds, which can provide abundant feeding opportunities. These adaptable birds often prefer areas with a mix of shallow and slightly deeper water for hunting, alongside undisturbed areas for roosting.

Fish make up most of the diet, captured close to the water surface after an aerial search. Prey size is relatively large compared with that taken by smaller terns. Crustaceans and other animal foods are occasional additions rather than the main resource. They typically swallow smaller fish headfirst in flight, but will carry larger prey to a perch or the nest before consumption. Common prey items in coastal areas often include mullet, sardines, and anchovies, reflecting local fish availability.

Common name

Caspian Tern

Scientific name

Hydroprogne caspia

Animal group

Birds

Size

48-60 cm long; 127-145 cm wingspan

Weight

530-780 g

Lifespan

Not reliably established

Status

Least Concern

Identification

Its very large size, heavy red bill with a dark tip and dark outer underwing distinguish it from Croatia's smaller, slimmer terns. Its prominent black cap extends from the bill to the nape during breeding season, often appearing streaky or patchy outside of it. The flight is powerful and direct, with strong, rather stiff wingbeats, unlike the more buoyant flight of smaller terns.