If you have been fortunate enough to see baby black howler monkeys, you will remember that they are born yellow-brown in color like the mom. Later, the male will turn dark in color. So, black howlers are dimorphic which means you can tell the difference between the two sexes. Also, the males are larger than the females.
They are known for their loud, barking guttural howls. If you are visiting the tropical rainforest in Central and South America where howler monkeys live, and you hear them, they might be further away than you think. That is because they can be heard from over three miles away! The sound is made by air being forced through the large hollow hyoid bone in the throat. It is thought that they howl to identify where they are, and try to avoid any confrontation with other groups. They are the largest monkey in Central and South America. Robin Brockett, former director of the Wildlife Care Center in Belize, witnessed that in the group of howler monkeys in Belize, they usually vocalize for about 10 minutes. Howler monkeys are territorial and if they are near another group, the howling can last up to one hour. It is very exhausting for the male. The females sound like creaking doors. The male howler monkey is the loudest land animal in the world. The only animal reported to have a louder sound is the blue whale!
They have a long prehensile tail, which means their tail is adapted to be able to grasp or hold objects. They use this as an extra arm to grab branches. The end of the tail is hairless, and the skin is marked with ridges kind of like fingerprints. No old-world monkeys have a prehensile tail.
Robin Brockett also witnessed howler monkeys holding hands. Once they held hands, they form a very close bond. She also noticed that they hardly ever groomed themselves. They were incredibly good smelling animals probably because their diet was 80% leaves. They have a scent like steeped black tea. They probably have this scent because the leaves have tannin and so does tea. Leaves are not a particularly nutritious food, so they have to eat a lot of them. They have a very long digestive track to get the nutrients out of this low nutrient food. They will also eat fruit when it is in season, and if they are able to get it from the tree before another troop of howlers or other animals eat the fruit.
Sometimes a rehabilitator working with howler monkeys, training them to be released back into the wild, might have to look like she is eating leaves to teach the very young howler monkeys what to do with the leaf, and which leaves to eat. The rehabilitators have to act like the monkey's mom and be able to make the correct vocalizations. The babies purr while sleeping if they are content. Howlers in Belize eat about 75 different species of leaves, which is a very small proportion of the amount of plants growing in this area. Howlers are also particular in the age of the leaves that they eat.
If you are fortunate to be able to walk through the tropical rainforest in Belize, see if you smell some black steeped tea! #howlermonkey #blacktea