What causes the hoatzin to smell?

The hoatzin, a unique bird native to South America, is known for its distinct odor, which is often compared to manure. This smell primarily arises from its diet, which consists mainly of leaves and other plant material that ferment in its specialized digestive system. The hoatzin has a unique adaptation where it possesses a large crop that houses bacteria, aiding in the fermentation process, thus producing the characteristic odor. This smell serves as a deterrent to potential predators, helping the bird avoid being eaten.