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by Terry Dunn

Howler monkeys are named and known for the loud, guttural howls that they routinely use at the beginning and end of the day. They are the loudest animal in the New World and while their howl is not a piercing sound, it can travel for three miles through dense forest.

Black howler monkeys are inhabitants of Latin American rainforests, ranging through eastern Bolivia, southern Brazil and Paraguay, and northern Argentina. They are the largest monkey in Latin American rainforests; they grow to be about two to four feet tall and weigh from eight to twenty-two pounds. They have big necks and lower jaws, where their super-sized vocal cords are housed.

Howler Monkey on a tree limb

Male howler monkeys use their big voices to defend their turf. Howls by one troop are answered by other males within earshot. Every-one starts and ends the day by checking out where their nearest competitors are. In this way, they protect the food in their territory. It’s an important job because their diet is made up mostly of leaves—not a particularly nutritious food. Finding young, nutritious leaves is a priority. Fruit and flowers are also valued so it’s crucial that the troop stakes its claim on these treasures when they are found.

Interestingly, when there are few howler monkeys in an area, the howling routine takes on a different pattern. In Belize, where black howler monkeys were reintroduced into a wildlife sanctuary, the howler monkeys were heard only a few times a week rather than every day. Apparently, with plenty of space and no other howler monkeys, there was no need to check on the whereabouts of competitors. As the population grows and new troops are established, there will be more reason to check in with the neighbors. At the Zoo, keepers will use recorded howler vocalizations from a distance to try and elicit the territorial calls from the monkeys as they would do in the wild.

Despite the volume of their howl, it’s disorienting to try to find a troop of loud howler monkeys in the wild. They hang out in the treetops where younger, greener leaves are abundant. However, if you do find yourself in the rainforest and it seems that an unusually large amount of fruit is falling from above or a fine spray of urine rains down on your head, you will know you are close!