Common Tern vs Sandwich Tern

In short

The most reliable field mark to separate Common Tern from Sandwich Tern is the bill: Common Tern has a slender orange-red bill with a black tip (adults, except some subspecies), while Sandwich Tern shows a longer, stouter black bill with a distinct yellow tip (adults) or all-dark in juveniles. In flight, Sandwich Tern appears noticeably paler and larger, with a longer, shaggier crest and a more buoyant, languid flight style, while Common Tern is more compact with a brisker, more direct flight. Juvenile and immature birds are best separated by bill color and the scaly pattern on the back and wings of young Sandwich Terns. Both species can be found together on coasts, but Sandwich Tern is generally more marine and less likely inland. Voice is also a good separator: Sandwich Tern gives a loud, grating 'kear-ik', while Common Tern has a sharper, more piercing call.

Identification tips

1. Bill color and shape (adults): Common Tern has a slender orange-red bill with a black tip (except in some black-billed subspecies), while Sandwich Tern has a long, stouter black bill with a yellow tip. This is the most reliable mark in adults.
2. Bill color (juveniles): Juvenile Sandwich Tern has an all-dark, thick bill (sometimes yellowish at the base), while juvenile Common Tern has a slimmer, dark bill without yellow or a thick base.
3. Size and structure: Sandwich Tern is larger, longer-necked, and heavier, with a more robust appearance. Common Tern is smaller, more compact, and has shorter legs and bill.
4. Crest: Sandwich Tern shows a long, shaggy black crest, especially in breeding plumage, while Common Tern has a neat, flat black cap with no crest.
5. Upperwing pattern (adults): Sandwich Tern's upperwings are very pale grey with broad white margins on the inner primaries (wearing to a 'hook tip' in late summer). Common Tern shows a darker wedge on the primaries as the breeding season progresses.
6. Juvenile/immature upperparts: Juvenile Sandwich Tern has a scaly pattern on the back and wings, lacking in Common Tern. This is a key mark for young birds.
7. Tail: Both have forked tails, but Sandwich Tern's is less deeply forked and has dark tips in juveniles, while Common Tern's tail is longer and more pointed in adults.
8. Leg color: Common Tern has bright red legs (adults), while Sandwich Tern's legs are black and shorter.
9. Flight style: Sandwich Tern flies with slow, buoyant wingbeats and long glides, often appearing languid. Common Tern has brisk, direct, and stiffer wingbeats.
10. Plumage in non-breeding season: Sandwich Tern develops a very white forehead after the post-breeding moult, more extensive than in Common Tern.
11. Voice: Sandwich Tern gives a loud, grating 'kear-ik' or 'kerr ink'; Common Tern's call is sharper and more piercing.
12. Habitat: Sandwich Tern is almost always coastal or marine, rarely inland. Common Tern can be found at inland lakes and rivers as well as coasts.
13. Perched jizz: Sandwich Tern stands taller, with a longer neck and shaggier crest; Common Tern is more compact and sleeker.
14. Primary wear (late summer): Sandwich Tern's white fringe on the primaries wears to a 'hook tip', a subtle but useful mark in late summer.
15. Pitfalls: Beware of distant birds—size and bill color can be hard to judge. In mixed flocks, always check bill color and crest shape first, then look for size and flight style.

Size

Sandwich Tern is distinctly larger: 36–41 cm in length with a 95–105 cm wingspan and weighing 200–300 g ([wikipedia]). Common Tern is smaller and more lightly built, with a shorter bill and legs, and less robust overall structure ([wikipedia], [avonet]). The size difference is usually obvious when seen side by side, but can be tricky at a distance or with lone birds.

Plumage

• Juvenile/First-winter: Juvenile Sandwich Terns have a scaly pattern on the back and wings, dark tips to the tail, and an all-dark bill (sometimes yellowish at the base). Juvenile Common Terns lack this scaly pattern and have a more muted upperwing, with less contrast and a paler rump. The bill in young Common Terns is dark but not as thick or long as Sandwich Tern.
• Adult breeding: Common Tern adults have a black cap, pale grey upperparts, white underparts, and a slender orange-red bill with a black tip. Sandwich Tern adults have a black shaggy crest, very pale grey upperwings, white underparts, and a long black bill with a yellow tip.
• Adult non-breeding: Both species develop white on the forehead, but Sandwich Tern's forehead becomes extensively white after the post-breeding moult, while Common Tern's cap recedes less dramatically. Sandwich Tern remains paler overall, with a longer, more prominent crest and a stouter bill.
• Flight: Sandwich Tern looks very pale in flight, with broad white margins on the inner web of the primaries (wearing to a 'hook tip' in late summer), while Common Tern has more contrast on the wing, especially a dark wedge on the primaries as the season progresses.

Behaviour

Sandwich Tern is more marine, often seen feeding further offshore and rarely venturing inland. Its flight is buoyant and graceful, with long glides and languid wingbeats. Common Tern is more versatile, frequently found on inland lakes and rivers as well as coasts, and has a brisker, more direct flight with stiffer wingbeats. When perched, Sandwich Tern often stands taller and appears longer-necked, with a shaggier crest, while Common Tern is more compact and sleeker.

Habitat

Common Tern breeds and forages in a wider range of habitats, including inland lakes, rivers, and coastal areas across temperate and subarctic regions. Sandwich Tern is more strictly coastal, breeding in colonies on sandy or shingle beaches and feeding mainly at sea. Overlap can occur at coastal sites, but Sandwich Tern is much less likely inland.

Voice

Sandwich Tern has a distinctive, loud, grating call described as 'kear-ik' or 'kerr ink', which is very different from the sharper, more piercing 'kree-ar' or 'krrr' of Common Tern. If you hear a harsh, grating call among terns, it's likely Sandwich Tern; Common Tern's call is thinner and more abrupt.