The beach flock graze peacefully knowing the guardian high up in the tree will alert them if danger arrives. One expects this kind of behavior for humans who we like to think are family orientated. If you watch a crow murder you will see there is always someone up high or to the side watching. Usually, I see more than one even.
Check out what I mean by multiple watchers. Here on the vertical tree are four more watchers. One is about to go feed and soon will be replaced by another. If you look into the distance a little there is another pair up on the driftwood also doing guard duty.
Crow murders are a tight pack and they watch out for each other through thick and thin.