Seagulls were a type of Terran bird.
Seagulls were known to fly near the San Francisco Bay. (Star Trek IV: The Voyage Home)
The recreation room, the basis for early Federation holodecks, incorporated seagulls into its beach program as early as 2270. (TAS: "The Practical Joker")
While searching for rogue Changelings on Earth in 2372, Odo flew in the skies over Starfleet Headquarters as a seagull. Commander Benteen found his impersonation convincing. Odo thanked her but didn't think the other gulls were fooled. "Admiral Leyton" then suggested that if Odo continued to practice, he'd fool the birds in no time. (DS9: "Homefront")