For some animals, the motivation for joining together is defence.

A flapping, pirouetting flock of birds, for instance, can make it harder for a hungry falcon to home in on a single victim. Similarly, a thundering, shifting herd of wildebeest can be an intimidating — and confusing — sight to a hungry lion. And in both cases, there are more eyes to keep on the lookout for attackers. There is, indeed, safety in numbers.