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 ...

Their calls are amplified by an enlarged hyoid bone in their throat, allowing the sound to travel over three miles through dense jungle. Howler monkeys use these calls to warn rival troops of ...

MEXICO CITY--It’s so hot in Mexico that howler monkeys are falling dead from the trees. At least 83 of the midsize primates, who are known for their roaring vocal calls, were found dead in the ...

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.