Sandwich Tern vs Great Crested Tern

In short

The most reliable field mark between Sandwich Tern and Great Crested Tern is the bill: Sandwich Tern has a black bill with a yellow tip, while Great Crested Tern shows a longer, thicker bill that is greenish-yellow throughout. For immature birds, focus on the upperwing: juvenile Sandwich Terns are scaly above with dark tail tips and an all-dark bill, while juvenile Great Crested Terns have a more variegated wing pattern with dark bars and a yellowish bill. Great Crested Tern is also noticeably larger and bulkier, with darker upperparts and a shaggier crest. In flight or at rest, pay close attention to bill color, size, and the patterning of the upperparts and head, especially in non-breeding and young birds.

Identification tips

1. Bill color and shape: Sandwich Tern always shows a thin, sharp black bill with a yellow tip (adults); Great Crested Tern has a much longer, thicker bill that is greenish-yellow throughout. This is the fastest check in good light for adults.
2. Juvenile bill: Juvenile Sandwich Terns have an all-blackish bill (sometimes with a yellowish base), while juvenile Great Crested Terns already show a yellowish tinge.
3. Upperwing pattern (juveniles/immatures): Juvenile Sandwich Terns are scaly above, with pale grey upperwings and less black on the crown. Great Crested Tern juveniles have a variegated upperwing with dark bars and a more complex pattern, plus a dark bar on the inner flight feathers after the first moult.
4. Tail tip (juveniles): Juvenile Sandwich Terns have dark tips to the tail, a feature not mentioned for Great Crested Tern.
5. Crown and forehead (adults, all seasons): Sandwich Tern has a full black cap in breeding plumage, receding to a white forehead in winter. Great Crested Tern always shows a white forehead, even in breeding plumage, with a shaggier, more pronounced black crest at the rear.
6. Upperparts color: Sandwich Tern is pale grey above; Great Crested Tern is noticeably darker, with battleship-grey upperparts.
7. Primary feather edges (adults): Sandwich Tern has a broad white margin on the inner web of the primaries, which wears to a 'hook tip' in late summer. Great Crested Tern lacks this feature.
8. Size and structure: Great Crested Tern is much larger, bulkier, and longer-billed. If seen together, the size difference is obvious.
9. Flight jizz: Sandwich Tern is more buoyant and delicate in flight; Great Crested Tern is heavier and more powerful, with longer, broader wings.
10. Leg color: Both have black legs; not useful for separation.
11. Crest shape: Great Crested Tern's crest is shaggier and more pronounced at the rear; Sandwich Tern's is less so.
12. Underparts: Both are white below; not a useful field mark.
13. Vocalizations: Sandwich Tern gives a sharp, grating call; Great Crested Tern is deeper, more crow-like. Useful if calls are heard well.
14. Habitat/context: If seen in tropical/subtropical Old World colonies, especially with other large terns, Great Crested Tern is more likely. In temperate Europe, Sandwich Tern predominates.
15. Pitfalls: Beware of non-breeding and juvenile plumages, as both species show more white on the forehead and can look similar at a distance. Focus on bill color/shape and upperwing pattern for best separation.

Size

Great Crested Tern is substantially larger: 46–49 cm in length with a 125–130 cm wingspan and weighing 325–397 g. Sandwich Tern is medium-large for a tern, but smaller overall: 36–41 cm long, 95–105 cm wingspan, 200–300 g. The size difference is obvious when seen together, with Great Crested Tern appearing bulkier, longer-billed, and heavier-bodied.

Plumage

• Juveniles and immatures: Juvenile Sandwich Terns have a scaly appearance on the back and wings, dark tips to the tail, and an all-blackish bill (sometimes yellowish at the base). Their upperwing is pale with less black on the crown. Juvenile Great Crested Terns have a head pattern similar to winter adults (white forehead, black crown), but the upperparts are strongly patterned in grey, brown, and white, with closed wings showing dark bars and a variegated look. After the first moult, young Great Crested Terns still show a dark bar on the inner flight feathers, unlike the plainer, scaly look of young Sandwich Terns.
• Adults (breeding): Sandwich Tern adults have pale grey upperwings, white underparts, and a black cap with a thin, sharp black bill tipped yellow. Great Crested Tern adults have darker, battleship-grey upperparts, a white forehead (even in breeding plumage), a shaggier crest, and a long, thick greenish-yellow bill.
• Adults (non-breeding): Both species show increased white on the forehead, but Sandwich Tern's black cap recedes more extensively, while Great Crested Tern retains a white forehead merging into a peppered black crest and mask.
• In flight: Sandwich Tern looks paler above, with a broad white margin on the inner web of the primaries (wears to a 'hook tip' in late summer). Great Crested Tern is darker above, with no such white margin, and appears bulkier and longer-winged.

Behaviour

Both species are highly vocal and nest in dense colonies, often with other terns. Great Crested Tern is more likely to be seen in large, noisy groups along tropical and subtropical coastlines, and its larger size and heavier flight are apparent when mixed with other terns. Sandwich Tern is more buoyant and delicate in flight, with a lighter build and shorter legs.

Habitat

Sandwich Tern breeds and forages mostly in temperate coastal areas, while Great Crested Tern is found along tropical and subtropical coasts from South Africa through the Indian Ocean to Australia and the central Pacific. Overlap is limited, but both can occur in mixed tern colonies along suitable coastlines. Context may help, but is not diagnostic where ranges overlap.

Voice

Both are loud and vocal in colonies. Sandwich Tern gives a characteristic grating "kear-ik" or "kerr ink" call. Great Crested Tern's main call is a loud, raucous, crow-like "kerrak"; it also gives a "korrkorrkorr" at the nest and a hard "wep wep" in flight. The calls are similar in function but differ in tone: Sandwich Tern is grating and sharper, Great Crested Tern is deeper and more crow-like.