Science Spotlight: Schooling & Flocking

by Teresa L. Carey

Schooling fish, such as the tight bunches of anchovies and sardines found in Monterey Bay, uniformly dart away from predators, make hairpin turns, and accelerate or stop without colliding. Such fish, as well as dense flocks of birds and swarming insects, follow “collective animal behavior” to move in these patterns.

There is an evolutionary benefit to this behavior. For many species, there is safety in numbers. Dunlins, common shorebirds, shift in their flocks and flash their light underbellies to startle predators. A sardine has a higher chance to survive in a school, and schooling minnows can find food faster.

Fish in these collectives monitor their neighbors’ movements and decide each motion based on signals from two sensory systems: their eyes, looking outward from both sides of the head, and the “lateral line,” a sensory organ running the length of the body, which detects vibrations in the water.

Ecologist Iain Cousin of Princeton University filmed and mapped the visual fields of fish. Hundreds of fish move together, but each individual only coordinates its movement with its immediate neighbors, he found. Any member of a school may make the first move and the rest follow along.

Tight flocks of hundreds or thousands of birds do the same, Andrea Cavagna of the Institute for Complex Systems in Rome has shown. Starlings in a flock pay attention to six or seven neighboring starlings, keeping a uniform distance between them.

UC Santa Cruz diving instructor Lee-Roy Haarhaus often sees schooling fish in Monterey Bay. “It is hard to describe how they do it,” he says. “Diving through the kelp forest and looking up to see a hundred rockfish is one of my favorite moments.”