Meet the bird that not only thinks it’s a cow, it also smells like one too. Hailing from the swamps of South America, the hoatzin (pronounced wat-seen) is an eclectic, handsome, albeit highly quirky, bird that divides its time between eating vast quantities of vegetable matter and just lounging around afterwards. Nothing is ever done in a hurry with hoatzins.
Of all birds, the hoatzin has baffled experts more than most. Even with recent advances in DNA testing, no one really knows what it is closely related to. It was once classified as a game bird (uazin is the Aztec word for ‘pheasant’), then as a member of the cuckoo family and then as a dove, but today it has its very own order called Opisthocomus, which means ‘ones with long hair behind’ in reference to its prominent crest.
The hoatzin is the only bird in the world that lives almost entirely on a diet of leaves. The hoatzin’s crop – a food storage pouch near the throat, found in most birds – is enormous, fifty times larger than its stomach and accounting for almost a third of the bird’s body weight. The crop is a fermentation chamber; like the foregut of a cow, it is full of enzymes and bacteria that help break down the tough cellulose within the leaves. When it comes to digestive matters at least, hoatzins have much more in common with cattle than with their feathered relatives.
Leaves are not really a suitable food source for a bird. They contain very little nourishment, especially when compared to meat or seeds, and they take a long time to digest. In fact, it may take a hoatzin nearly two days to completely digest one meal of leaves, the slowest of any bird. This explains why they spend around 80% of their time just loafing around doing nothing in particular, spreading their wings wide to soak up the sun as they digest their large meals.
And that’s not the only drawback to their unusual diet. The huge crop reduces space for flight muscles, which makes hoatzins poor flyers – they are laboured and awkward in the air and often crash land in a comical fashion. Meanwhile, the fermentation within the crop produces a smell akin to cow manure, which has earned them the name of ‘stink bird’.
Awkward and unconventional though their lifestyle is, the hoatzin is nonetheless a very successful bird. Leaves, while notoriously difficult to digest, are plentiful and available all year round. And the fact that they smell quite bad also works in their favour, since this makes their flesh unpalatable and keeps them mostly out of the food chain. Even humans don’t like the taste.
Most specialists, thriving on only one or two select food items, are intricately linked to their food. This makes them highly vulnerable, and nowhere is this more apparent than in the case of the giant panda, which famously eats almost exclusively bamboo. But, thankfully, that isn’t the case when it comes to the hoatzin. It seems as though this avian enigma will be around, breaking the trend (and smelling quite bad), for a long time to come.