Mystery Creature Revealed – the Hoatzin

Last week’s mystery creature, a very unusual looking bird, was the Hoatzin (Opisthocomus hoazin). Well done to six-year-old David who knew what it was. David is an avid animal lover who currently lives in Singapore.


Image credit: Bill Bouton, Image source: wiki commons.
  • Hoatzin are very unusal among birds for a variety of reasons and have intrigued scientists since they were first described in 1776, by German zoologist Statius Müller. Here are just some of facts about these amazing creatures.
  • Hoatzin are herbivores – but most of their diet consists of leaves, which is unique among birds. In order to digest this cellulose rich diet they have a digestive system more similar to cows (and ruminants) than to any other bird.
  • They have developed very large crops and the leaves they digest are fermented within their digestive systems. This process begins in their crop and is aided by anaerobic bacteria found throughout their guts, which feed on the leaves and help break down the tough cellulose within them.
  • They digest their food very slowly and are often seen sitting around, appearing to do very little at all.
  • The development of their large crop to aid digestion comes at a price; these birds have little space left in their chest and their breast-bones are very simple. Their pectoral muscles are small and weak. These are the muscles that power flight, so these birds are poor flyers and appear quite awkward and ungainly.
  • There is one other thing about their diet and digestion that makes these birds very distinctive, it is their smell! They are often referred to as Stink Birds, as the fermentation of leaves does not create an odour that humans find attractive. Because of this foul smell, people have no wish to eat them so they are not hunted. Sometimes it pays to be smelly!
  • Hoatzin live very social lives, often found in large flocks of up to 40 birds. They are found in the rainforests of the Amazon – usually in trees along a river or beside a lake or some other water source. They are very vocal birds with a variety of sounds from calls, to hisses, grunts and croaks.
  • The appearance of the Hoatzin is very striking and gives them the reputation as a ‘pre-historic’ bird. They have bright blue faces with dark red eyes. They have a strip of long feathers on their head, a crest, giving them a mohawk-type feature. They belong to the family called Opisthocomidae which comes from the greek for ‘have long hair behind‘ – referring to these mohawk styles.
  • Hoatzin are so unique among bird that they are the only species in this Opisthocomidae family.
  • The chicks of these birds have claws on their wings (wich disappear after about three months). If the nest is threatened the chicks will often flee and hide, they are even able to escape to the water if necessary and are good underwater swimmers. Once the coast is clear they will use their clawed wings to help them climb back up a tree, to the nest.
  • Based on their dinosaur-like appearance, and the wing claw of their chicks, there has long been a fascination with the evolution of this bird. Some thought they were the link between reptiles and birds. Others thought they were a modern day version of the Archaeopteryx, a bird attributed as an evolutionary step from dinosaur to bird. There were also similarities in appearance between the Hoatzin and the Archaeopteryx. Recent genetic sequencing of Hoatzin genome now suggests that it is the only surviving member of a lineage that branched off some 64 million years ago (not long after many dinosaurs became extinct) and that it evolved its traits indepedent of the archaopteryx lineage.


I found this one of the most fascinating Mystery Creatured to date, I hope you enjoyed it too. As always, if you have any suggestions for the Mystery Creature spot, please get in contact! 


Science blogger and writer; Owner of Dr. How's Science Wows; Mother of three junior scientists who have taught me that to be a great scientist you need to look at life through the eyes of a child!