How to identify the Sandwich Tern

To correctly identify the Sandwich Tern (Thalasseus sandvicensis), check each of these features. Birds can be tricky: habit, habitat, and call often confirm a sighting that a single photo cannot.

Size at a glance

Length

35-45 cm (14-18 in)

Wingspan

85-97 cm (33-38 in)

Weight

180-300 g (6.3-10.6 oz)

Physical features to check

1. 1

   Plumage

   Overall feather coloration and pattern.

   Adult breeding plumage features a white body, pale grey upperparts (mantle and upperwings), and a prominent glossy black cap extending from the forehead to the nape, often with shaggy crest feathers. The underparts are pure white. Non-breeding adults lose the full black cap, which becomes streaked with white, and the forehead turns white. Juveniles have mottled grey-brown upperparts, a dark carpal bar, and a less defined black cap.

2. 2

   Beak shape

   Shape and color of the bill: a key field mark.

   Long, slender, and sharply pointed. Black with a distinct yellow tip in adults. Juveniles may have a duller bill with less prominent yellow.

3. 3

   Eye color

   Iris color and any distinctive eye markings.

   Dark brown

4. 4

   Leg color

   Leg and foot color.

   Black

5. 5

   Distinguishing features

   Standout features that separate this species.

   The black bill with a yellow tip is the most distinctive field mark for adults. Its shaggy black crest in breeding plumage, pale grey upperparts, and white underparts are also key. In flight, the long, narrow wings and buoyant flight are characteristic.

6. 6

   Juvenile appearance

   How young birds differ from adults.

   Juveniles have a mottled grey-brown back and upperwings, often with dark scaling on the mantle feathers. The crown is dusky, not a solid black cap, and the forehead is whitish. A dark carpal bar (a dark patch on the leading edge of the wing) is often visible. The bill is duller, sometimes entirely dark, with the yellow tip developing later.

7. 7

   Seasonal changes

   Plumage variation between breeding and non-breeding seasons.

   Breeding adults have a full, glossy black cap. Non-breeding adults (from late summer through winter) develop a white forehead, and the black cap becomes streaked with white, often appearing more like a dark patch on the nape and hindcrown.

8. 8

   Sexual dimorphism

   How males and females differ.

   Males and females are generally monomorphic in plumage and size, though males may be slightly larger on average.

Key field marks

• Bill Color. Look for the distinctive black bill with a yellow tip in adults. This is the most reliable field mark.
• Plumage (Adult Breeding). Observe the glossy black cap with shaggy crest feathers, pale grey upperparts, and pure white underparts.
• Plumage (Adult Non-breeding). Note the white forehead and streaked black cap, which becomes less prominent.
• Size and Shape. Medium-large tern with a slender body, long, narrow, pointed wings, and a relatively long, forked tail.
• Flight Style. Watch for its buoyant, graceful flight and characteristic plunge-diving feeding method.
• Vocalizations. Listen for the harsh, grating 'kirr-ik' call, especially in colonies.
• Juvenile Plumage. Look for mottled grey-brown upperparts, a dusky crown, and a dark carpal bar on the wings.

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