Status: Least concern
Length: 25.59 in (65 cm)
Weight: 35.2 oz (997.9 g)
Range: Amazonian South America
The smell is a mystery. Or not the smell exactly, but where, evolutionarily, it came from. Looking over the branches of the phylogenetic tree, so to speak, it isn’t easy to locate the so-called stinkbird’s perch. Historically it was placed with the pheasants, much later with the turacos, a frugivorous African family whose members include a few noisy birds named for an alarming cry that sounds remarkably like go away. More recently, fossil evidence has turned up a Namibian ancestor for this South American bird, from the extinct genus Namibiavis, but the problem of how the hoatzin became the only extant species in its family, and indeed its whole order – let alone how its ancestors came to straddle both sides of a formidable ocean – is still far from settled.
But back to that smell, redolent of cow manure or fresh hay. This part of the mystery has proven easier to solve, even if the conclusions are no less bizarre. The hoatzin is exceedingly rare among birds – indeed, it’s the only one like it – in that when it comes to diet its closest relatives are ruminants: cows, sheep, antelopes, deer, and even giraffes. Like other animals that chew the cud, hoatzins have evolved organs – in this case, a dramatically enlarged crop – where the otherwise indigestible (and nutrient-poor) leaves on which they feed ferment before, having been broken down by bacteria, they pass through the rest of the esophagus, the gizzard, the small intestine, and, eventually, out through the cloaca. The process is long and the birds – as a result both of their slow digestion and the smaller flight muscles necessitated by their enormous guts – are fairly sluggish much of the time.
As disagreeable as their odor may be, their physical appearance is equally striking, even off-putting. Some might say the hoatzin is an ugly bird, but perhaps its spiky Mohawk and blue eye shadow are just more punk rock, less repulsive than in your face. And to be sure, the hoatzin is an anti-establishment bird, refusing, according to one ornithologist, to follow the rules of evolution. Even the chicks buck convention, hatching with a pair of incongruous claws on each wing. These they use to climb up and down trees, shedding them only when, as adults, their clumsy, cape-like wings are strong enough to fly, if not fly well.
Good punks that they are, hoatzins aren’t poseurs. They don’t care what we think of them, their smell or their style or their hoarse, grunting calls. Least interesting of all, to the true stinkbird, are our explanations, the reasons we give or derive or imagine for its mysteries, the billions of base pairs of its DNA we sequence – when really, when the meltdown is coming and the wheat is growing thin, what’s the point? Your cities are drowning and I, croaks the Hoatzin, I live by the river.
from The Hater’s Guide to Birds, with illustrations by Annie Hagar.