This is a Tern. Three match your description but since you talk of a black plume, it is the Elegant Tern. Two others are similar- Royal and one other.
A bird that looks like a seagull is called a tern.
A bird that looks like a smaller version of a seagull is called a tern.
Crow
The bird you are describing is likely a White Ibis. They have a long, curved orange beak, orange legs, and white plumage, similar to a pelican but with a slimmer body shape. White Ibis are commonly found in coastal marshes and wetlands in the southeastern United States.
Utah has named the seagull the official state bird.
The tern is a bird that resembles a seagull in appearance.
seagull
I am not a 100% sure but I think a gaviata is a really large bird, that looks like a seagull. Glad 2 help! if I did.
Seagull eggs are many differernt colors but the main colors are creamy white with brown and tan speckles on them.
Each seagull has their own unique personality.
seagull
Pigeon.