Howler monkeys are among the loudest creatures in the new world. Despite their small size (up to 20 pounds), their calls can be heard several miles through dense tropical forest due to an enlarged hyoid bone in their necks. These herbivores are quite social and prefer to travel in groups of a dozen or so. It is anticipated that some of the endangered species of howlers will become extinct in our lifetime. You can categorize their howling sessions into different groups, depending on the time of day or their moods. This example demonstrates the most drone-like mode, and occurred during a lazy afternoon shortly before a heavy rain.