From: itannman@boris.ucdavis.edu (Ann Mansker)
Subject: Critter of the Week: Opisthocomus hoatzin
Date: 18 Aug 1998 00:00:00 GMT
Newsgroups: ucd.life

The hoatzin ( http://www.lastfrontiers.co.uk/images/venezuela/k_hoatz.jpg
) is found in the Amazon rain forest, nesting at the edges of streams.  It
is an ungainly, disheveled-looking bird, and is said to smell bad -- the
local name translates to "stinkbird".  At present, the bird's place in
avian classification is unclear; to quote the Handbook of the Birds of the
World, Vol 3:  "The problem is that the Hoatzin is so aberrant in both
morphology and behaviour that it does not fit satisfactorily alongside any
other group of living birds."

This confusion is fueled by several unique characteristics.  The hoatzin
is the only avian ruminant, subsisting on a high-volume but nutritively
poor diet of leaves.  It survives by stuffing large quantities of leaves
into its crop, where they are crushed and fermented.  Once that process is
complete, the mash is passed to the stomach and gut for normal digestion.
One study estimated that this process allows the bird to digest and
utilize up to 70% of the mass of food it ingests in just a couple of days.

As mentioned, hoatzins nest along streambanks.  The nests actually
overhang the water.  When threatened, the chicks leap out of the nest into
the stream, an extremely unusual behavior for an arboreal species.
Fortunately, unlike the adults, the chicks are good swimmers.  Once danger
has passed, the chicks clamber back into their nests.  In this they are
aided by another unique feature, a pair of claws at the wrist of each
wing. No other bird still has wing claws (the "thumb" and "forefinger'),
and the hoatzin loses them at maturity.

There is an amusing article on the pleasures of hoatzin research at
http://www.nwf.org/nwf/intlwild/hoatzin.html .