what are some enemies of howler monkeys?

Hello! Howler Monkeys might sound pretty impressive,
but they are often hunted by human beings. I personally believe that these
folks are the species main predators. However, the harpy eagle, other large
carnivorous birds and the boa constrictor will also prey on it every now and
then. Hope this helps and all the best!

Howler monkeys are the loudest of all monkeys. They call to let others know where their territory is, alerting them to stay away. The calls sound like a loud whooping bark or roar. After one group of howlers call, another group answers. Howler monkeys usually do this in the morning and at the end of the day. 

Their enemies include humans, lions and tigers.