Baboon troop movements are 'democratic'

The study, led by researchers from Smithsonian Tropical Research Institute, Oxford University and Princeton University, is the first to simultaneously GPS track members of a group of primates.

Despite baboon groups having a hierarchical social structure the study discovered that all individuals have a say over where the troop goes, including those with low social status. It also found that females have as much influence on troop movements as males.

A report of the research is published in this week's Science.

The researchers fitted 25 members of a wild baboon troop in Kenya with GPS collars that recorded each individual's location once per second for 14 days. The team recorded 20 million GPS data points showing how these baboons moved relative to each other.

The team then analysed pairs of baboons and identified where one individual moved away from the troop and whether it 'pulled' its partner in this new direction. If successful such individual 'pulls' can trigger a cascade of movement potentially causing a sub-group and eventually the whole troop to follow. However, where the other baboon in a pair remained 'anchored' to the spot the baboon initiating the movement would return.

Patterns in these movements showed that animals with higher social status did not have a greater chance of attracting followers. When conflicts arose, with individuals pulling in different directions, the group would compromise by taking a 'middle way' between the preferred directions when the difference between them was less than 90 degrees. When the difference was greater than 90 degrees they would chose the direction taken by the majority. This suggests that baboons use similar movement rules to many other animals, such as fish and birds.

'It seems that, despite their complex social structure, when it comes to disagreements over where to move it’s a case of 'one baboon, one vote' as decision-making is largely a shared, 'democratic' process,' said Dr Damien Farine of Oxford University's Department of Zoology and the Smithsonian Tropical Research Institute, joint first author of the research with Ariana Strandburg-Peshkin of Princeton University. 'Patterns of collective movement in baboons are remarkably similar to models that can predict the movements of fish, birds, and insects, which use a simple set of rules such as 'follow your neighbour'.'

Co-author Meg Crofoot, Smithsonian Tropical Research Institute research associate and assistant professor at University of California Davis, said: 'Our results illustrate a really important distinction between social status and leadership, and show that egalitarian decision-making processes – where many or all group-members have a voice – can be important, even in highly stratified societies.'

Whilst, in deciding where to go, it seems for baboons the majority rules the researchers say that more work needs to be done to understand what motivates individual baboons to 'pull away' in the first place and whether individuals might sometimes be able to 'work the system' and disproportionately influence the troop's decisions.