Consider this: shiners have a natural preference for darkness. Plop a shoal of them into a pool of water, and they’ll head for the shadiest bits. This is something that animals do all the time: They track gradients in their environment. A migrating robin might follow the Earth’s magnetic field, a moth might follow the scent of a flower, or an ant might track the pheromones laid by its nest-mates. But single shiners are laughably bad at this.
Andrew Berdahl and Colin Torney from Couzin’s team discovered their ineptitude by projecting shifting patterns of light over a shallow pool and adding the shiners in increasing numbers. Overhead cameras tracked their movements, and the team calculated how good they were at chasing the shadows.
The solo fish did so badly that they were almost swimming randomly. Only larger shoals were good at avoiding the shifting light. Even then, Berdahl and Torney found that the shiners’ movements were far more influenced by what their neighbours were doing, than by how bright the environment was.
Excerpt from an article written by Ed Yong at Phenomena. Continue HERE