For centuries, farmers have known that their livestock not only gather in large herds but also tend to face the same way when grazing. Experience and folk wisdom offer several possible reasons for this mutual alignment. They stand perpendicularly to the sun’s rays in the cool morning to absorb heat through their large flanks, or they stand in the direction of strong winds to avoid being unduly buffeted and chilled.

But cows and sheep don’t just line up during chilly spells or high wind. Their motivations for doing so during warm, pleasant and unremarkable weather, or indeed in the dead of night, have been a mystery until now. In a new paper, Sabine Begali from the University of Duisburg-Essen in Germany