gray-backed tern vs trinta-réis-de-bico-preto

The Grey-backed Tern and Gull-billed Tern can be distinguished by their bill shape and plumage. The Grey-backed Tern has a more slender bill and a distinctive grey back, while the Gull-billed Tern has a stout, all-black bill and pale grey upperparts.

Bill shape: The Grey-backed Tern has a slender bill, while the Gull-billed Tern features a stout, all-black bill. Plumage: Look for the grey back of the Grey-backed Tern versus the pale grey upperparts of the Gull-billed Tern.

The Grey-backed Tern has a grey back, which contrasts with its white underparts, while the Gull-billed Tern has pale grey upperparts with a white body. The Grey-backed Tern's plumage is more uniform in color, whereas the Gull-billed Tern's wings are pale grey with slightly darker primaries.