As a sheep munches on the grass, it has to make important decisions. However, we may not think of sheep as being widely known for their decision-making ability. But to a sheep, the decision to get its head down to munch grass or get its head up to look for wolves, or any hungry predator including the rustler with his truck and plans to sell lamb chops and legs of mutton, is just that. More heads up time means less food, simple but, as always, the risk assessment gets difficult at the boundary between hunger and security.
A part solution to the problem is to flock together and cooperate on sentry duty, and this has been universally adopted from time immemorial. At first sight, the bigger the group the better. With everyone doing their bit, the defense cost to an individual flocker is lower if the flock is larger. This is known as the ‘group size effect’ and as size matters, the flockers will make bigger flocks.
The problem is complacency. Doing your bit for defense in a flock or herd is voluntary, and if there are huge numbers, an individual has less incentive to volunteer. “Not my turn” can be baa’ed too often and a sneak attack from wolves intent on civilizing the flock can occur. Last Friday, a study of the problem was published (1). The authors were Michelena and Deneubourg from U libre de Bruxelles.
Firstly, their study showed that sheep do what sheep do. The tendency to vote with your neighbor resulted in more heads up awareness. Secondly, they highlight the challenge each individual has in balancing public and private information. It is this balance that governs the tempo, that is, whether lots of short heads down are favored over one long head down. The speed of information spread through the social network is key so setting a tempo which will minimize the response time to an attack while keeping the defense cost at a tolerable level. More sentry duty, less green stuff.
- http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0018631
