How marmosets scurry through treetops

Ever wondered how tree-dwellers so deftly navigate the flimsy branches and untrustworthy twigs that characterise the arboreal life?

A study into marmosets, by Jesse Young at the Northeast Ohio Medical University and colleagues and published in the Journal of Experimental Biology, offered some clues. The charismatic monkey species switches its peculiar stride to stay branch-bound.

The research focused on the common marmoset (Callithrix jacchus) – a small-bodied Brazilian monkey with a unique way of moving through their treetop environments.

They tend to gallop or bound across branches using asymmetrical leg movements, rather than the more symmetrical, diagonal pattern used by other primates.

Previous studies had looked into the effects different branch thickness can have on a tree-dwelling animal’s balance and ability, but “compliance” – that is, how bendy a branch is – hadn’t been the focus of much research.

So Young and his team filmed two adult marmosets in 3-D as they traversed poles of varying thickness and flexibility, simulating tree branches of different sizes.

The team then modelled the movements to observe how locomotion changed.

They found that when crossing branches that were thinner and more flexible, the monkeys slowed, used more symmetrical movements, and held their footing on surfaces for longer periods rather than allowing themselves to become airborne.

Interestingly, the monkeys also lowered their centre of gravity on thinner poles, holding their bodies closer to the branch and reducing their “bound”, all of which offer a little more stability.

The researchers say the findings echoes previous studies of red squirrels and mouse lemurs, reinforcing the idea that branch flexibility and movement, not just thickness, are important variables in locomotive adjustments for tree-dwellers.