Sterna hirundo
Common Tern (Sterna hirundo)
Featured photocommon-tern.jpgSterna hirundo, the common tern, is a medium-sized tern of the family Laridae, distributed across the Northern Hemisphere. Adults are 31 to 37 cm long with a wingspan of 77 to 98 cm and weigh 110 to 145 g. The plumage is pale grey above and white below with a black cap and a sharp red bill. The IUCN lists the species as Least Concern. Common terns are agile aerial fishers, plunge-diving for small fish in coastal and inland shallow waters across most of the Northern Hemisphere.
Quick facts
- Habitat
- Coastal estuaries, salt marshes, freshwater lakes, and large rivers across the Northern Hemisphere. Breeds in colonies on sandy beaches, gravel islands, and shoreline marshes; non-breeding birds use coastal habitats worldwide.
- Range
- Breeds across most of the Northern Hemisphere — Europe, North Africa, central Asia, eastern North America, and parts of Atlantic Canada. Winters on coasts of South America, Africa, southern Asia, and Australia.
- Size
- 31–37 cm body · 77–98 cm wingspan · 110–145 g
- Plumage
- Breeding adults show pale grey upperparts, white underparts, a glossy black crown extending from the bill back through the eye, a bright red bill with a black tip, and red legs. Non-breeding adults show a paler black-and-white head with much-reduced black on the crown, a darker bill, and the tail less deeply forked. Juveniles show black-and-buff barring on the back and wings.
- Song
- A harsh, descending 'kee-arrr' alarm call given at colonies, plus various softer chattering calls during display. Common terns are highly vocal at breeding colonies.
- Migration
- Long-distance migrant. Northern breeders travel south to coasts of South America, Africa, southern Asia, and Australia for the non-breeding season. Annual round-trip migrations of 20,000-30,000 km are typical.
- Conservation
- Least Concern (LC)
Overview
Sterna hirundo is one of about a dozen Sterna terns worldwide and is the most widely distributed tern in the Northern Hemisphere. The species is one of the most familiar coastal seabirds across Europe, North America, and Asia. The common tern is closely related to and often confused with the Arctic tern (S. paradisaea), particularly in non-breeding plumage.
Distribution
The breeding range covers most of the Northern Hemisphere temperate and subarctic zone. The species is one of the most numerous terns at breeding colonies across Europe, North America, and Asia. Wintering grounds extend across the Southern Hemisphere — the species' migration is one of the longer documented among Northern Hemisphere terns. The 'common' English name reflects the species' wide distribution and population size, not its taxonomic position.
Plunge-diving
Common terns hunt by plunge-diving — the bird hovers briefly 1-10 m above the water surface, watches for movement, then dives bill-first into the water and seizes small fish near the surface. The technique is similar to the brown pelican's plunge-diving but the impact is much gentler given the smaller body mass. Successful dives capture a single fish; the bird returns to the air immediately after and either swallows the fish in flight or carries it back to a chick at the colony.
Sources & further reading (2)
- iucn-red-list — accessed 2026-04-30
- encyclopedia — accessed 2026-04-30
Frequently asked questions
How do common and Arctic terns differ?
Common and Arctic terns are very similar in size and plumage. Key field marks: common tern has a red bill with a black tip in breeding plumage (Arctic tern has an entirely blood-red bill); common tern has darker grey-tipped underwing primaries (Arctic tern has clean white-edged primaries); common tern has slightly longer legs (visible when both species are perched). Voice differences are subtle but useful when known.
Why are common terns called 'sea swallows'?
Several European languages use a 'sea swallow' name for the common tern, including the Latin epithet 'hirundo' (Latin for 'swallow'). The convention reflects the species' deeply forked tail, sharply pointed wings, and rapid, agile flight — all reminiscent of the much smaller swallows of the family Hirundinidae. The two groups are not related; the resemblance is convergent evolution on aerial-pursuit-of-flying-prey lifestyles.
How long do common terns migrate?
Annual round-trip migrations of 20,000-30,000 km are typical. North American Atlantic-coast breeders winter on the coasts of South America (from Brazil to Argentina). European breeders winter in West Africa. Asian breeders winter in southern Asia and northern Australia. The migration is one of the longer documented among Northern Hemisphere terns, though shorter than the truly extreme Arctic-tern migration.
