Smoothly and silently, a green parrot snake slithers toward its prey, well camouflaged amongst the Amazon arboreal vegetation. Stealth stalking is an essential hunting technique in the dense Brazilian rainforests, but this meal appears particularly easy. While the snake glides across the branch with ease, the fledgling Hoatzin haplessly clambers away in an effort to escape, taking every step with such nervous caution that it would seem living in the trees was unnatural. Upon reaching the branch's end, the newborn bird seems doomed; it has not yet acquired the ability to fly, and the snake lurks just meters away, ready to strike. Yet, the legless predator never gets its chance to attack. The Hoatzin tumbles off the branch, plummeting into the river below.
This short freefall into the Amazon tributary initially appears to be an appropriate last act for such a clumsy creature, an untimely misstep that saved the bird from death by digestion but would undoubtedly lead to death by drowning. Just moments later, however, this seeming miscalculation is revealed to be a perfectly calculated escape strategy. The young Hoatzin pokes its tiny head above the surface of the water, paddles toward a nearby branch, and uses a pair of claws on each of its wings to climb out of the river and back to the safety of its nest.
These claws are not only an invaluable attribute for fledglings, but an autapomorphy - an exclusive trait among all species of extant birds. While the exact evolutionary history of Hoatzins remains unresolved, there can be no argument that their claws are an anachronistic adaptation that would seem more fitting on an aerial ancestor. Within a matter of months, these claws will disappear as fully feathered wings develop, but the bird becomes no less bizarre in comparison with its contemporaries.
The external appearance of Hoatzins can be described using any number of words, but most would be synonymous with 'strange.' Measuring an average of 65 centimeters (25 inches) long, adults are comparable in size to pheasants, with bodies covered in grayish-green and chestnut plumage and a tail of rusty brown feathers. A long neck looks more furry than feathery along the throat and ends with a distinctly small head - the strangest physical feature of all. Behind a silver beak shaped like a tomahawk, the Hoatzin has two large, maroon eyes, each centered on a round patch of featherless blue skin; atop this head is a crest of no more than two dozen thin, rufous spikes.
All along the banks of rivers, lakes, and streams in the northern Amazon Rainforest - especially surrounding the Amazon and Orinoco deltas - these prehistoric-looking birds are plentiful. Perched in trees overhanging the water, Hoatzins look awkward no matter how they move. When grounded, they maneuver along branches with no comfort or confidence. In flight, they only last short distances and lack any semblance of beauty or grace. This ineptitude at flying is the direct result of an unusually large crop, which is so disproportionately big that it displaces the flight muscles and keel of sternum.
What the crop costs the Hoatzin in flight capacity it significantly makes up for as a survival mechanism. When the birds feast on the leaves of tropical legume plants, bacteria stored in the crop breaks down cell walls to enable digestion. In this function, the crop acts as a rumen, making Ophisthocomus hoazin the only avian species to employ foregut fermentation as part of its digestive cycle.
While this foregut fermentation is crucial to eating, it is equally invaluable in ensuring that the Hoatzin is not eaten. Given the bird's inability to escape predation upon reaching adulthood, it would seem an easy meal for the various species of snakes, hawks, monkeys, and humans seeking meat in the Amazon jungles - yet most of these threatening animals generally keep their distance. Hoatzins protect themselves with an invisible shield of stink, a putrid odor produced when the aromatic compounds in legume leaves are broken down. Smelling like manure, the species has earned the nickname of Stinkbird and is only hunted during times of desperation.
It is mostly thanks to this repelling aroma that the Hoatzin remains an unthreatened, commonplace sight throughout the northern Amazon, a region where most species of wildlife are facing daily decimation. Any area with proximity to water poses as a potentially prime nesting ground, and small colonies of up to forty birds most often develop in swamps and mangroves. Making no effort to conceal themselves, Hoatzins communicate loudly and freely through a range of gruff groans, grunts, croaks, and hisses.
When an invasive individual attempts to encroach on a neighbor's claimed terrain, these calls escalate. Despite their social nature, Hoatzins are steadfastly territorial, and mated couples often defend their home turf together through threatening noises and body postures. During the rainy season, between November and March in South America, mated parents usually have two to four eggs to protect. Laid in nests strategically constructed on tree branches overhanging the water - in case fledglings need to escape danger - these eggs are incubated for 28 days before hatching.
In the ensuing weeks, both parents play an active role in caring for their offspring. After several months, however, maturation does not necessarily mean independence. Hoatzin children commonly remain with their parents for a few years, building a strong family unit by providing additional care and protection for their future siblings. Ultimately, all Hoatzins will leave their birth nests to establish lives of their own, ready to create many future generations of foul-smelling, bizarre-looking birds.
An adult female Hoatzin watches as one of her two unfledged chicks rises from a river and ascends through a tangle of branches returning to the nest. Chicks will literally jump into the body of water, over which the birds' stick nest has been built, if they are threatened. They are capable of swimming under the surface and can return to the nest on their own. The young birds use both feet and still-functional-juvenile wing claws in the process. These claws will wither and cease to be functional as an adult.
Swamps, mangroves, and rainforests in northern South America, especially in Amazon and Orinoco deltas
Leaves (mostly of tropical legume plants) and fruits
The bacteria in the crop also provide essential nutrients to Hoatzin fledglings; parents will shift these bacteria into their stomachs, where they consolidate into a sticky substance that is subsequently regurgitated and fed to the baby birds.
Hoatzin fledglings are slow to take up the art of flying, often taking more than two months to gain airborne abilities.
The Hoatzin is the only member of the genus Opisthocomus, which is Greek for "wearing long hair behind."
The Hoatzin is the national bird of Guyana.
Due to its development of claws and physical resemblance, Hoatzins are most often likened to the Archaeopteryx, a prehistoric animal that is considered the first link between reptiles and birds.