They can use this tail as an extra arm to grip or even hang from branches—no Old World monkeys have such a tail. A gripping tail is particularly helpful to howler monkeys because they rarely ...

Normally quite intimidating, howler monkeys are muscular and can be around ... The veterinarian put ice on their limp little hands and feet and hook them up to IV drips with electrolytes.

My adventure of a lifetime began in 2015 when I was asked to follow the tree-top lives of Costa Rica’s gravity-defying howler monkeys (Alouatta palliata palliata). Image by Justine Allan.