Why bison put their females in charge

Amandine Ramos

Why bison put their females in charge

Standing 2 meters tall and weighing as much as 1000 kilograms, European bison (Bison bonasus) are impressive animals. These cousins of the American bison—nearly driven to extinction in the last century—are being reintroduced in small herds across Europe, leading some farmers and forest managers to worry that the large herbivores will destroy their habitat. To better understand how the bison decide when and where to move, scientists studied a herd of 43 individuals in the Reserve Biologique des Monts-d’Azur in the Alpes-Maritimes region of France. They recorded the animals’ movements for 4 hours daily, identifying leaders, what type of action led others to follow, and where the herd moved. The herd wasn’t guided by a single leader, the scientists report in the November issue of Animal Behaviour. Instead, any individual regardless of sex or age could prompt the group to move, although most decisions were made by adult females—as is the case with most ungulates. A bison shows that it plans to change its location by taking at least 20 steps without stopping or lowering its head to graze. A potential leader was most likely to be followed if it walked in the direction that most of the others were facing—suggesting that bison vote with their feet. The researchers suspect that most leaders are adult females because they require higher quality food when lactating or pregnant. Wildlife managers can use this research to reduce human-bison conflicts, the scientists say. They need only identify a herd’s leaders, fit them with GPS collars, and install a virtual fence of alarms and electrical shocks. It should then be possible to control the leaders’ movements—and, thus, those of the entire herd.

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