The Mexican howler (Alouatta palliata mexicana ) is a subspecies of the mantled howler, A. palliata. This subspecies is found predominantly in forests between south eastern Mexico and north eastern Peru. Typical of its species, the Mexican howler monkey has a prehensile tail, a deep jaw, and a large pharynx which it uses to make characteristically deep and resonating howls. Mantled howler monkeys are known for forming unusually large cohorts averaging 14 members and sometimes extending to 40 members.
This howler monkey species has compensated for its adapted digestive system by minimizing energy output as much as possible. The Mexican howler exhibits limited interaction with members of its species and very minor aggressive behavior. There is evidence of physical aggression between members of the species during migratory periods or changes in dominance. Males, when fighting for dominance, have been observed to target juveniles, sometimes even killing them, and physically injuring older males. For a younger male to take control of a group, he must first kill the dominant male, exhibiting extensive aggression. Females also show aggression when asserting dominance, though this is usually limited to harassment behavior like hair pulling and biting.
The Mexican howler can eat a remarkable variety of foods including leaves, flower, buds, petioles, and fruits. This subspecies of howler monkey is known to be a frugivore and a behavioural folivores. Their digestive system is slow and they have significantly fewer enzymes for protein and fiber digestion than other frugivores, but they compensate for this by selectively eating leaves with less fiber. Consequently, much of this the Mexican howler monkey's activity is dedicated for foraging for fruit and young leaves which it can easily digest. Frugivory is typically observed in New World monkeys instead of Old World monkeys, but howler monkeys are an exception to this categorization.
