Elegant Tern
Thalasseus elegans
This is a medium-large tern, with a long, slender, slightly downcurved orange bill, pale gray upperparts and white underparts. It is 39–42 cm (15–17 in) long with an 76–81 cm (30–32 in) wingspan, and a weight of 190–325 g (6.7–11.5 oz). Its legs are black. From late summer to winter, the forehead becomes white. The black of the crest that comes down from the crown extends through the eye, creating a small black "smudge" in front of the eye even in winter plumage. On royal terns, the black crest stops at the eye, while lesser crested tern has a less shaggy crest.
ID text from Wikipedia, CC BY-SA 4.0
Sandwich Tern
Thalasseus sandvicensis
This is a medium-large tern, 36–41 cm (14–16 in) long with an 95–105 cm (37–41 in) wingspan, which is unlikely to be confused within most of its range. The weight ranges from 200–300 g; males average slightly heavier than females, but with much overlap. The thin, sharp bill is black with a yellow tip. Its short legs are black. Its upper wings are pale grey and its underparts white, and this tern looks very pale in flight, although the primary flight feathers darken during the summer.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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