Five gulls and a crab

So gull No.1 is swimming around just outside the rocks at low tide. Gull No.2 is poking in the rockweed that covers everything, then finds a good-sized crab and begins battering the thing with its beak and tearing off legs. Lunch lasts about 3 minutes, until gull No. 3, much larger, swoops in and claims. His (it must be a male, don't you think?) lunch lasts somewhat longer, until he's apparently had enough and swims magnificently off, abandoning the wreckage not to gull No.3, who has completely retreated, but to gull No.4. By now there must be close to nothing left. Yet gull No.5 hangs hopefully around on the next rock over.

I speculate about males and females, dominance and survival. Four of the gulls look more or less identical, and when lunch is over, sit separately, all looking in different directions. Is it a harem? The avian equivalent of a Boy Scout troop? The Scoutmaster is clearly different, bigger, bolder, etc, and may even be a different species. I go into the house and pick up Sibley for the ID, and am confronted with pages and pages of birds that look remarkably similar. Sibley devotes a long, high-lighted box to the problem of gull identification, and starchly says: "A casual or impatient approach will not be rewarded."

I am rebuked, gulled (if you will) by a crab. My 20 amateurish minutes of pseudo-science and pleasure in the sun have not passed muster, and I retreat to my own lunch of tuna on wheat, and an hour of fancy with Bernard Cornwell's Excalibur.