Were there any previous landings where people noticed wildlife on the ship?
From a legal standpoint, they are protected by the migratory bird act. From a PR standpoint, what kind of backlash could SpaceX face if they roasted some seagulls on live stream?
Almost certainly no. We all saw the booster continue to show flames/engine activity after entry burn shutoff on the broadcast. So most likely explanation is a malfunction. Also, birds tend to fly away when really loud, hot bright things approach them. And finally, finally, that droneship was in international waters, I believe.