The howler monkey who I showed yesterday who was scurrying along the wire stopped for a moment and looked back. He was checking on the rest of the pack of howlers.
Howler monkeys usually travel in groups. We typically see about a dozen at a time. When they start hooting and howling it is an amazing experience. They can be heard more than one mile (1.6 km) away. The loud, deep howls sound like they must originate from something as large as a train engine, not a crature as small as a howler monkey.
We have photos of our experience seeing the Opera in Paris posted on our Viva la Voyage travel photo site this week.