Interesting gull behavior (1 Viewer)

For the last couple of weeks or so, I've noticed some interesting behavior in the Western Gulls where I work. As always, they rob people and other gulls for their food. When chasing other gulls, like Heermann's, This species likes to spiral upward faster than the larger Westerns can follow. The Ring-Bills simply out maneuver them in normal flight.

Recently I've noticed Western Gulls chasing Heermann's Gulls relentlessly. The smaller Heermann's is usually pursued by about 3 or 4 Westerns at a time. The Heermann's they chase never has any food. In fact it can be seen with it's beak slightly open as it's trying to keep it's breath. The spiraling behavior never seems to work in this situation either. It always takes place in late afternoon. The chase is very fast; the Western Gulls taking turns as they seem to be trying to wear the smaller gull out. Once I saw a Heermann's Gull land because it was simply exhausted, it was soon set upon by two of the Western Gulls that was chasing it. They began thrashing it on the ground but because they too were quite tired, the Heermann's got away...barely.

I don't know if it's the same Westerns chasing the same Heermann's or not. There is a rather badly beaten up Heermann's Gull walking around the park that's missing many tail feathers and has many puncture wounds on it. Not sure what caused this birds unfortunate injuries but it seems consistent with an attack by another bird or birds.

Western Gulls do have a hatred for Heermann's Gulls because they often chase Western Gulls over open water. They think they're Jeagers at that point. Over any land however their behavior changes and they're more like Ring-Billed Gulls.

Has anyone else noticed this type of "gang mobbing" mentality in the gulls around them? I know Great Black-Backed Gulls can be this way but what about other species?

So the other day, I believe it was the day after Christmas; I was at work again and saw about four Western Gulls, this time terrorizing a Brown Pelican which had just taken off from the small pier we have on the bay. They followed it until it got about 30 feet high as it flew along the shoreline bordering the north end of the park. Then they began to attack it. First dive bombing it then actually jabbing their bills into it's back and once on the head. The poor pelican almost crashed into the crown on a tree! It then veered off to the right, going out over the bay, the whole time the gulls kept up their assault. I watched until they all flew behind the building and trees out of sight.

I am assuming at this point that they are the same gang of gulls.