Rigor Vitae: Life Unyielding

Saturday, July 29, 2006

THE ELEMENTARY HOATZIN

As we approached the crowns of a submerged copse of trees, I heard a dyspeptic lowing, like a steer with frothy bloat. My arms burned from hours of hard paddling and I was relieved to have reached our destination. We were in Peru, on the flooded Yarapa River, not terribly far upstream from where it merges with two other rivers, the Ucayali and the MaraƱon, to form the Amazon. Two gringos were being led to a nest of Hoatzins (Opisthocomus hoazin) by a local who found us the night before, and seduced us with Hoatzin tales. Octavio had grown up here, and he made his living guiding tourists. Taking on such a guide is always a gamble, but Octavio proved to be a first-rate naturalist (pleasant surprise), and an even better boatman (no surprise). We began paddling upriver an hour before dawn. Despite rowing solo, Octavio's canoe spent much of the trip stopped, waiting for us to catch up. We heard the crazed, mournful call of a pottoo (Nyctibeus sp.). All along the banks, crimson eye-shines betrayed the presence of dozens of Common Caimans (Caiman crocodilus), and further up the river we saw a crocodylid so huge it could only have been a rare Black Caiman (Melanosuchus niger). By the time we got to the nesting area we were well into the day. We sliced through a lagoon filled with spectacular Victoria Lilies (Victoria amazonica), their six-foot leaves upturned at the edges to reveal pink, spiny undersides. At the far edge of the lagoon was the nest. It was just past the peak of the wet season, and we floated on twenty feet of water where we could have walked six months earlier. We heard the mooing of the adult Hoatzins for fifteen minutes before we first spied one of the birds. The size of a Plymouth Rock hen, it was equally skilled at flight. Its buffy plumage was set off by a bright blue, naked face and rufous wings like a peacock's. The most striking feature, though, was the long, Medusine crest, feathers snaking up like tentacles.

The classification of the Hoatzin has been the subject of argument for centuries. Many have assumed it to be related to the pheasants, while others (including me) suspected an affinity with the cuckoos and their kin. I've seen no wild birds as clumsy as Hoatzins save the Madagascan couas (cuckoo cousins). They also bear a strong resemblance to the touracos, which were long assumed to be cuckoo relatives. Based on DNA hybridization, Sibley and Ahlquist agreed, placing them in the order Cuculiformes, along with the cuckoos and anis. In their recent radical taxonomical overhaul, Fain and Houde placed them in the new clade Metaves, along with pigeons and flamingos. Whatever living birds are the Hoatzin's closest relatives, they're not close at all.

Hoatzins are fun to watch. Their shyness does not take on an aspect of wildness. Looking very much like chickens, they wobble uncomfortably on their perch, putting off taking flight as long as possible. If they can, they'll clamber away awkwardly, preferring to keep lots of branches between themselves and a viewer, and it's quite tough to get a good photograph of one. Part of the reason they fly so poorly is morphological. Where the chests of most birds are occupied by a deep keeled sternum and massive pectoral muscles, in the Hoatzin, this region is devoted largely to an enormous crop, where resident bacteria break down cellulose in the leaves these birds eat: a fermentation tank, much like the rumen of a cow. This fermentation process imparts a foul smell to the birds, a fact that probably compensates for their incompetence at escaping enemies. Breeding Hoatzins live in groups of several birds, all of which attend the nest, which probably frequently contains offspring from three or more adults.

We finally reached the nest, an untidy stick platform seven or eight feet above the water's surface. Octavio climbed from his canoe into the tree, while the adults scolded from afar in a decidedly unintimidating manner. As he approached, three young birds of various ages left the nest. The oldest bird could fly nearly as well as an adult, and wasted no time in leaving the area. Next came bird #2, the only one I managed to photograph. It climbed onto a branch, tiptoed about clumsily for a moment, then scrambled off, knock-kneed, into the foliage. The youngest bird was quite small. It dove from the nest, directly into the water, and was not seen again. At this point, we decided it was best to turn back, and allow the family to reconstitute. I have no idea how long it took, but the youngest Hoatzin surely rose again to the surface, and climbed back up the nest tree, assisted by Archaeopteryx-like claws at the bend of each wing. These claws degenerate quickly, and are barely discernible by the time the bird can fly, but for the first couple of weeks of its life, the Hoatzin is a most unbird-like climbing and diving creature, possibly carrying on the lifestyle of a long dead Mesozoic ancestor.
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All photographs taken by CPOBvK in Yarapa region of Peru, 1997

1 Comments:

Anonymous Pamela said...

Great post, very evocative--I don't know if I'll ever be paddling on a river in Peru looking for a hoatzin, but I feel a little closer now.

8:43 AM  

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