Prey species have a whole bag of tricks to keep from becoming dinner. Fish school, birds flock, mammals herd. The idea is that a predator needs to pick out one individual to concentrate on in order to maximize success. Most predators make a kill only about one in ten tries at best. So, if you are bunched up and moving at top speed, the predator you are trying to avoid will lose you in the crowd. At least that's the theory. But predators have tricks up their proverbial sleeves as well. School of fish crowding into a tight ball so any individual is lost? Attack the whole ball like swordfish and marlin do. Lash about in a crowd and you are certain to hit something which can be eaten at leisure. Humpback whales go one better; they swim below the packed school of fish, and blow a stream of bubbles while circling the base. This "bubble net" serves to pack the school even more densely and the whale comes up from below, mouth open, to engulf the whole shebang.
I was beach combing at Bethany last fall when I saw a flock of sanderlings swirling up in a tight spiral. At first, I thought it was smoke until my eyes made out the individual birds. Sanderlings are those tiny sandpipers everyone sees at the beach but no one really notices. One of several related species of small sandpipers, known to birders as "peeps", they run up and down the beach, always staying just out of the wash of the surf. Running like clockwork toys, they examine each new swatch of wet sand for any tiny mole crab or other crustacean exposed by the receding wave. In fall, they form small flocks, some of which stay along the mid Atlantic, others travel to points south. The flock I was watching spiraled even tighter when a peregrine falcon appeared from out of nowhere. The sanderlings had seen it and recognized it for what it was and were taking the only defense they knew -keep moving, keep shifting. They seemingly moved in precise unison. Ornithologists originally thought flocking birds were telepathic by the way they seem to move as a single unit. Researchers, using high speed movies, were able to notice how one bird begins the move with the nearest neighbors mirroring it. The movement ripples across the flock too fast for the unaided human eye to see.
A peregrine can outfly any bird in the sky, so fleeing was not an option. The peregrine dove through the spiral, splitting it in two. The two smaller flocks, still spiralling, separated and the falcon dove through the smaller of the two. The birds veered as one and kept the tight spiral. All but one - too old keep up, too young to recognize the signals,or just plain out of luck. One sanderling found itself alone. The Japanese have a saying: "the lone nail gets hammered down". The falcon knew this and now had a single individual on which to concentrate. While the rest of the flock, knowing they were safe, sped down the beach, the lone peep, in a final defensive maneuver, dropped like a rock onto the water. The peregrine hovered over the hapless sanderling floating on the surface, and with all the grace and precision of a dinner party guest picking up a canape, plucked the peep from the surface and quenched it in one great yellow talon. The falcon flew up-beach to pluck and devour its meal. The sanderlings settled back down on the beach to continue their clockwork minuet with the waves, searching for tidbits.
Everybody eats. Everybody dances.
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