The pheasant-like hoatzin is the only bird species that ferments its food, an unusual digestive system that also makes it the stinkiest bird in the world.
The hoatzin is a very strange bird. Native to the backwaters of the Amazon, its chicks are born with clawed wings, it is the last surviving member of an ancient bird line believed to have branched off on its own around 64 million years ago, and its diet consists only of plants, which is very odd for birds. But this living oddity is most known for its strong manure-like smell, which has earned it the nickname ‘stinkbird’. The hoatzin is the only known bird species with a foregut fermentation system similar to the one found in cows, which releases significant amounts of methane via constant burping. The smelly burps and particularly stinky droppings give the hoatzin its signature odour.
In most birds, the crop is a food storage pouch near the throat used to regurgitate small amounts of food to feed chicks, but in the hoatzin, it is much larger and acts as a fermentation chamber for the leaves it ingests. Inside are specialist bacteria that break down the swallowed foliage, which takes a total of 45 hours to be completely digested. During this unusually long digestive process, the bird releases gases via burps that produce its distinctive manure-like odor.
The hoatzin’s crop is so large that it hardly leaves any room for flight muscles, which explains why adult birds can only take flight for short periods of time, mostly to travel from one tree to another, and why they prefer to clumsily hop and climb between branches, which is where their wing claws come in handy.
But how stinky is the world’s stinkiest bird? Well, apparently, their manure smell is enough to keep away hunters, as well as other predators, although some, like the Great Black Hawk, and the weasel-like Tayra, are more than willing to deal with the stink for a meal.
Interestingly, in 2024, scientists analyzed and mapped the genomes of more than 360 bird species to create a family tree of major bird groups, but the hoatzin, along with shorebirds and cranes, didn’t fit in with any other groups.
