Howler Monkeys Make Noisy Neighbors In Costa Rica

When we moved to Costa Rica we didn’t know we’d move right next to raucous neighbors who’d set off car alarms in the middle of the rainforest. But that’s what howler monkeys do — wake up the neighbors. And according to Wikipedia, there are at least 15 species of these large monkeys found throughout the rainforests of Central- and South America.

Male Golden Mantled howler monkey strolling across the lawn at the Caña Blanca Wildlife Sanctuary in Golfo Dulce, Costa Rica. Image license CC SA 3.0 by Steven G. Johnson via Wikimedia Commons

Howler monkeys in Costa Rica

Here, you find the Golden-Mantled howler monkey (Alouatta palliata) and the Ecuadorian mantled howler (Alouatta palliata aequatorialis.) And let me tell you, both are equally loud. They are so loud, in fact, that their calls can be heard as far as three miles away, National Geographic reports. They like to greet the dawn with this racket. While it’s not certain, they may be the loudest animals in the world.

Female Mantled howler Monkey with her infant. Image license CC 2.0 by Steve Harbula via Wikimedia Commons

And while females can call when they have a mind to they are not nearly as loud as the males, and it’s largely the males who are responsible for this non-musical din.

What makes male howler monkeys so loud?

The thing that I’ve observed about these guys is that they don’t really howl, even though they really are exceedingly loud. Instead, their calls are one part pig-like grunt, one part braying donkey, one part roar, and another part I don’t know what the h*ll. However, the first time I heard a male calling, I remember wondering what the heck a pig was doing up in a tree. Then it dawned on me that it wasn’t a pig.

You can see (and hear) what I mean in this video:

I went outside with binoculars to have a look, and sure enough, I found a troop of these critters whooping and hollering up in the trees.

Size really does matter…for male howler monkeys, anyway

Male monos congos (their traditional name here) have throats that are quite large, and those throats are equipped with shell-shaped vocal chambers that allow them to turn up the volume as needed. Add to that a specialized hyoid bone in the throat, and you have the makings of a very vociferous creature because this bone acts as a resonating chamber. And this is a male howler’s way of telling other monkey troops that this territory is already claimed.

But the thing about the different howler monkey species is they can be pretty diverse when it comes to their living situations. Some species maintain harems, where one male mates with several females. And in these instances, the challenge is to keep the females interested and also keep other males away. This is where all that yelling comes in handy. Other species of howler monkeys have a different living situation, where females can choose as many mates as they want. In this scenario, the males’ calls aren’t so loud.

Some howler monkeys are swingers

And scientists have found a rather odd corollary here, MentalFloss reports. The louder the howler monkey call, the smaller his…um…private parts (this is a family website after all.) But yelling and sperm production are high energy activities.

Researchers made their discoveries by using 3D laser scans to measure the hyoid bones and testes of 10 species in a 2015 study. Howlers who maintained harems had larger hyoid bones and smaller testes, while the opposite was true for those with the swinger lifestyle. But the researchers admitted they weren’t really sure how this trade-off came about, the study’s lead author, Jacob Dunn said in a press release.

“In evolutionary terms,” he said, “all males strive to have as many offspring as they can, but when it comes to reproduction you can’t have everything.”

So apparently one can’t have one’s evolutionary cake and eat it too.

And the monkeys go through all of this just for these cute babies:

Mom and youngster. Photo by Jan Hazevoet, taken in Guanacaste Province, Costa Rica. Image license CC 2.0 via Flickr

Breeding can occur all year long, but most babies are born in December and January and mom usually has one kid at a time. The golden-brown infants generally stay close to mom, not venturing more than two meters away from her. And howler moms are very good mothers. I watched one mother quietly hooting for her youngster to move closer to her and when it didn’t, she walked across the tree branch and grabbed it, making sure to keep the youngster safe from predators.


Those predators include humans (howler monkeys are still eaten in parts of Costa Rica, and of course, farmers kill them if they damage crops or eat chickens, which of course, they do.) Other predators include Jaguars, boa constrictors, and harpy eagles. Sadly, these beautiful and impressive birds are nearly extinct in Costa Rica due to the evils of deforestation, cattle ranching, and hunting by humans.

The harpy eagle is becoming increasingly rare in Costa Rica. Image license CC SA 3.0 by Mdf via Wikimedia Commons

Howler monkey troops consist of about 10-20 individuals, and while they can be found on the ground every now and then, they are almost exclusively arboreal, Arkive reports. As the largest New World monkey, males weigh between 4.5 — 9.8 kg (about 10 to 21 lbs.) In terms of size, adults are larger than housecats, with the very largest of males measuring 63 cm (24 inches) without that long tail. Which incidentally, is prehensile, meaning these guys can hang out. Females are lighter and smaller on average. And their preferred foods are fruits, flowers, and leaves.

You can watch this caring howler monkey mom with her little one in the video below.

Featured image license CC SA 3.0 by Steven G. Johnson via Wikimedia Commons

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