If seagulls fly over the sea, then what flies over the bay?

Bagels.

Wrong.

Seagulls imply the existence of Rivergulls, Lakegulls, Mountiangulls, Desertgulls, Forestgulls, Plaingulls, Valleygulls, Hillgulls, etc.

I think a "landgull" would just be a pigeon

I've seen many seagulls in my life.

But I've never seen any of the others.

And that's terrifying. Stay vigilant.

In light of the above, then, I hereby propose that squirrels get renamed to "treegulls."

It's all fun and games until the firegull nation attacks.

Don't forget heartgulls. Everyone always forgets heart.

Captain Planet Gull: "Give me those chips and I'll poop on you!"

You: "... don't you mean 'or' you will poop on me, not 'and'?"

Captain Planet Gull: ...

You: ...

Bay-gull. Bagel.

Don't forget THA GOOD SHIP MERRY GULL!

Most of what we consider "seagulls" dont actually go out to sea. It's all lies.

I never knew that. I thought it went from beagle to seagull and then on to eagle…

Long ago, the four gulls lived together in harmony. Then everything changed when the fire gulls attacked...

If there are armadillos, where are the legadillos?

I used to study animal management and there was a lecturer who wrote his uni thesis on "seagulls" and any time he heard someone call them seagulls he'd shout down the hallway "They're herring gulls!"

also, spacegulls

You have to go pretty far back (to proto-Celtic, it looks like) to find a linguistic ancestor for the word "gull" that doesn't just mean "that specific bird."

But in proto-Celtic, it looks like "weilanna" probably meant "wailer." As in, "one who wails," though we don't know exactly what the suffix "-anna" means. A similar word in that language would've been "wailos," which even though it sounds similar seems to have been unrelated to our modern term "wolf," as it comes from a different proto-indo-european root.

Anyway, the word "gull" does refer to the sounds that it makes more than anything else. So in figuring out what a landgull, airgull, and firegull might be, we need to find something noisy. Or just something annoying, given the derisive connotation of "wail."

Edit: This is, of course, assuming that we're looking for different existing types of animals to be these creatures, rather than just (for instance) creating new, elemental forms of gulls; or "reskinning" seagulls with different elements; or inventing all-new animals to fill those roles.