The booming call of a male howler monkey is one of sounds that typify the neotropical forests. From Belize, down through Central America through the Upper Amazon Basin and into Brazil’s Pantanal, there are six species of howler monkey.
In Belize, the black howler is a resident of lowland broadleaf rainforest as well as semi-deciduous forest. The male black howler is, as its name implies, is very black in color. The black howler has a very long coat of hair with a long prehensile tail that acts as a fifth hand, which is very useful for an arboreal species.
In Costa Rica, the mantled howler is the common howler species and they can be found over much of the country covered on our Costa Rica tours . They typically are not found above 2,500 meters in elevation. The male mantled howler is black with long rich reddish brown area of hair on its sides. This is the mantle thus giving the name to this very large monkey.
In the Amazon Basin, the red howler is fairly common and is much more frequently heard than seen. This monkey is highly arboreal and the males are reddish brown in color. Even though they are fairly large, they often appear small when observing them. This is because of the size of the trees where they may be observed. In a large cannon-ball tree, the red howler appears quite small but if close observation is permitted, the red howler is actually a fairly large monkey. Guests on our Amazon River cruises  are often treated to a glimpse of these primates during our frequent boat excursions.
In common, all of the howler monkey species have a very loud booming call. The black howler is regarded as having the loudest call in the neotropical forest. This is an amazing statement as there are incredible sounds that can be heard emanating from the forests throughout Central and South America. Birds, like screaming piha and the various parrots and macaws, can make incredibly loud calls. Bamboo rats and potoos also make loud and very unusual calls during the hours of darkness. Howler monkeys still hold the title of the absolute loudest call and like so many other things in natural history, the call has to be heard to appreciate it.
The feeding preferences for howler monkeys are also quite interesting. Howler monkeys are folivorous, meaning they feed quite extensively on leaves. Leaves are low in nutrients so large quantities must be consumed. In addition, howlers produce copious amounts of saliva to assist them in breaking down leaves prior to swallowing. Any additional help in leaf digestion is important and this is just one adaptation that howlers possess to assist them in their feeding. Young leaves are also more desirable as they are more easily chewed and digested and the young leaves do not contain as much leaf toxin as mature leaves. Many herbivores prefer young leaves and buds over mature leaves for these same reasons.
Naturalist Greg Greer  is a favorite among IE travelers, and has gained a reputation for his friendliness and good humor, along with his incomparable knowledge of natural history, photos and articles have been widely published in books and magazines, including Georgia Outdoor News, Bird Watcher’s Digest, Alabama Outdoor News, Riversedge and Southern Wildlife.