Why Do Sheep Follow Each Other? How Flocking Keeps Sheep Safe

Safety in numbers

Sheep descend from the mouflon, a wild sheep hunted by wolves, leopards, eagles and other predators. For animals like these, flocking brings several benefits. Many eyes spot danger sooner, a predator finds it harder to single out one target in a moving crowd, and each individual’s chance of being the one caught is smaller.

In 1971 the biologist W. D. Hamilton described the selfish herd idea: each animal tries to put others between itself and the danger, which pulls the group into a tight cluster. Sheep are one of the clearest examples. Predators such as the gray wolf usually target animals at the edge of a group or those that get left behind.

What the GPS study showed

In 2012, Andrew King and colleagues at the Royal Veterinary College in England fitted a flock of sheep and a herding dog with lightweight GPS backpacks that recorded their positions many times a second. When the dog approached, the sheep did not just run away at random. Each sheep moved toward the center of the flock, and the group bunched together tightly, exactly as the selfish herd idea predicts.

This shows that following and bunching are not mindless. Each sheep is reacting to its neighbors and to the threat in a way that improves its own chances.

Do sheep have a leader?

Most flocks do not have one fixed leader. Very often the leader is simply the first sheep to move, and the others follow. Once a few animals head in one direction, the urge to stay with them draws the rest along, which is why a flock can stream through a gate or along a path in single file.

Experience does count. Older ewes that know the ground, and ewes followed by their own lambs and grown daughters, tend to lead more often. Studies of grazing Merino flocks have found that they alternate between slow phases, when sheep spread out to feed, and sudden fast phases, when a few individuals start to move and the rest quickly pack together behind them.

Shepherds have exploited this for thousands of years. A trained wether, a castrated ram, wearing a bell would lead the flock on command. This bellwether gave English a word for anything that leads a trend.

How sheepdogs use flocking

Sheepdogs work with the flocking instinct, not against it. A Border Collie circles the flock at a distance, and the sheep respond by bunching together and moving away from the dog as a group. By positioning itself on the right side, the dog can gather scattered sheep and then drive the whole flock in one direction.

Computer models of shepherding have shown that a dog needs only two simple behaviors to do this: collecting sheep that stray from the group, and pushing the group from behind once it is together. The sheep’s urge to stay with their neighbors does the rest.

Why sheep hate being alone

Separation from the flock is one of the most stressful experiences for a sheep. An isolated sheep bleats loudly, paces, tries to see or reach its companions and may push through fences to rejoin them. Its heart rate and levels of stress hormones such as cortisol rise. Researchers studying sheep therefore try to test them with companions nearby, because a lone, stressed sheep does not show its true abilities.

Flocking behavior generally appears in groups of about four or more sheep. Sheep keep track of the group constantly, lifting their heads between mouthfuls of grass to check where the others are. This regular checking is probably what keeps a grazing flock together as it slowly drifts across a field.

Not all sheep flock the same way

Breeds differ. Merinos, bred on open ranges in Spain and Australia, form very tight flocks. Many British hill breeds, such as the Herdwick and Scottish Blackface, spread out more widely to graze sparse upland pasture, and each flock learns its own home area on the hills. Breeds that developed in places with few predators tend to show weaker flocking.

Compared with their close relative the goat, sheep are much more strongly bound to the group. Goats spread out and browse independently and are more likely to stand their ground, while sheep prefer to flee together.

Is following the flock a sign of low intelligence?

No. Following others is a sensible rule for a prey animal, and sheep can show impressive abilities when tested fairly, from recognizing faces to learning mazes. The evidence is summarized in Are sheep smart?. The instinct can occasionally go wrong, when a flock follows a frightened leader into danger, but in the wild it has kept sheep and their ancestors alive for millions of years.