Why do seagulls swarm?

Seagulls usually feel safer in packs. Usually when seagulls find food they swarm around it as a pack or group and eat it as a group. Seagulls do not, however, swarm people for any reasons because they are as afraid of them as they are of us. Seagulls are kind animals, but if they see a rat, it is dead meat.
For e.g., this would never happen with a seagull or group of seagulls.

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Shreik!!! Seagulls!

No, Joe, they are nice.

But one of them ate my toes off!

Ah, shut up.