The Common Tern, nicknamed the "sea swallow" for its graceful flight and forked tail.
The Acrobat of the Air
When you spot its graceful silhouette dancing above the water, there's something magical about watching a Common Tern (Sterna hirundo) in action. This elegant seabird, with its piercing calls echoing across our coastlines, lakes, and rivers, seems to announce that warmer days are here. People fondly call it the "sea swallow," and you can see why – there's that same effortless, aerial poetry in its movement. But here's the thing: beneath all that delicate beauty lies a surprisingly fierce hunter! You've probably witnessed it yourself – that heart-stopping moment when it suddenly rockets headfirst into the water, only to emerge triumphantly with a wriggling fish clasped firmly in its bright orange bill.
How to Identify the Common Tern
Identifying a tern relies on fine details, especially bill color and head plumage. It's often confused with its globetrotting cousin, the Arctic Tern.
In Breeding Plumage (Spring/Summer)
This is its best-known appearance. The adult sports a jet-black cap covering the forehead, crown, and nape. Its body is pale gray above and white below. The two key features are its slender, sharp, orange-red bill with a small black tip, and its long, forked tail that extends beyond the wings when perched.
In Non-Breeding (Winter) and Juvenile Plumage
In winter, the black cap recedes. The forehead turns white, leaving only a black "headband" at the back of the head. The bill becomes almost entirely black. The juvenile resembles a winter adult but has a more scaly pattern on its back.
In winter, the Common Tern's white forehead is a good identification clue.
Scientific Dimensions and Records of the Common Tern
Characteristic
Value
Length (beak to tail)
31-38 cm (12-15 in)
Wingspan
75-98 cm (30-39 in)
Weight
90-200 g (3.2-7.0 oz)
Average Lifespan (wild)
9-12 years
Record Lifespan (wild)
33 years
These dimensions highlight the Common Tern's slender and agile build, perfectly adapted for its acrobatic flight and plunge-diving fishing technique.
Flight and Fishing Technique
The tern's flight is what most distinguishes it. It is incredibly light, buoyant, and acrobatic, with deep wing beats. To hunt, the Common Tern hovers by beating its wings in place a few meters above the water. As soon as it spots a small fish, it plunge-dives, headfirst, to snatch it from just below the surface. It's an active and spectacular hunt.
Calls and Sounds
The Common Tern is a vocal bird, especially around its colonies. Its most common call is a sharp, two-part "kee-arr" or "kewik". It also produces a rapid, rattling alarm call when disturbed. These calls are essential for communication between pairs and for territorial defense.
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Not to be Confused with...
Although they often share similar marine and freshwater habitats, telling a Common Tern from its close relatives and gulls is straightforward once you know what to look for.
Arctic Tern
Bill: Entirely blood-red, with no black tip (in breeding plumage).
Legs: Shorter and darker red than the Common Tern.
Underparts: Often has a darker grey belly, contrasting more with white cheeks.
Wings: Narrower wings and longer tail streamers, giving a more elegant, buoyant flight.
To confidently distinguish a Common Tern, especially from an Arctic Tern, focus on these details:
The Bill Tip (Summer): This is the most reliable clue. The Common Tern has an orange-red bill with a distinct black tip. The Arctic Tern's bill is a uniform, blood-red color with no black.
Leg Length: The Common Tern has noticeably longer legs. This is easier to see when the birds are standing side-by-side.
Tail Streamers: When perched, the Common Tern's tail streamers are roughly the same length as its wingtips. In the Arctic Tern, they are often longer, giving it a more elongated rear.
Flight and Hovering: Watch its hunting style. The characteristic hover before a plunge-dive is a classic Common Tern behavior.
Wing Pattern in Flight: The Common Tern can develop a dark wedge on its upperwings as the breeding season progresses, and it often has distinct dark streaked wingtips. The Arctic Tern's outer wing can appear translucent.
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Habitat and Distribution
The Common Tern is a long-distance migrant, breeding in temperate and subarctic regions of Europe, Asia, and North America. It nests on coasts (sandy beaches, islets) as well as inland, near lakes, ponds, gravel pits, and along large rivers. It requires islets or nesting areas free of terrestrial predators and sometimes shares these freshwater habitats with birds like the Great Cormorant. It is strongly migratory, spending the winter in coastal tropical and subtropical regions of the Southern Hemisphere, reaching as far south as Peru and Argentina.
Distribution Map
The map below shows the global distribution of the Common Tern, indicating its breeding range (orange), areas where it is present year-round (resident, green), non-breeding/wintering grounds (blue), and migration routes (purple).
Conservation Status
Globally, the Common Tern is listed as "Least Concern" (LC) by the IUCN Red List of Threatened Species due to its large population and vast breeding range. However, its breeding populations are very sensitive to habitat degradation (coastal development) and human disturbance during the breeding season. Conservation programs, such as installing nesting rafts, help support local populations. While numbers in North America have declined sharply in recent decades, the overall global status remains stable.
Frequently Asked Questions (FAQ)
Why is it called a "sea swallow"?
This nickname comes from its flight silhouette, which resembles that of a swallow: a slender body, long pointed wings, and especially a very characteristic forked tail.
Is a tern a type of gull?
No. Although terns and gulls belong to the same large family, the Laridae, they are distinct groups (genera). They are cousins, but not the same. Terns typically have a lighter build, longer pointed wings, and a deeply forked tail, unlike gulls.
Where can Common Terns be seen?
From spring to autumn, they can be observed along coasts and on many inland waterways across North America and Europe. They are especially visible during migration as they travel to and from their wintering grounds in the south.
What does a Common Tern eat?
Like most terns, the Common Tern primarily feeds by plunge-diving for small fish, both in marine and freshwater environments. However, molluscs, crustaceans, and other invertebrate prey can also form a significant part of its diet in some areas.
