Maybe the white seagulls didnt feel comfortable around the brown seagull since the brown seagull probably hadnt shared the same experiences and have shared the same cultural background as the white seagulls have had as this species of mammals expressed in this Pod.
OMG! i saw the same thing a couple of days ago while i was having lunch along the pier. 2 white seagulls were sitting in the water, and when a brown seagull came to join them, the white ones went in to attack mode and chased off the brown one.
the brown seagull was persistent and would try to come back and sit with the white seagulls, but the white seagulls would still not let the brown seagull join them.
there was no food present, nor could i see anything else that the white gulls would have been protecting. i had to ask myself, "Am i witnessing racism in animals?!"