| A team of researchers led by UGA
psychologist Dorothy Fragaszy this past fall published the first
direct scientific report of tool use among a population of wild
capuchin monkeys. There have been reports of single instances of
this behavior but never of a whole population using tools routinely
over a long period of time.
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| The capuchin monkeys at this
Brazilian biological reserve make use of stones not found in
the area. Fragaszy hopes to learn if the monkeys transported
them there. |
Using heavy stones, possibly transported for this
purpose to an “anvil” site in northeastern Brazil, these
cat-sized monkeys routinely crack palm nuts, which grow in clusters
close to the ground. Though this nut-cracking behavior has been
common knowledge among local residents for years, this is the first
scientific report to confirm a behavior previously studied only
in wild populations of chimpanzees.
The study was published in the American
Journal of Primatology. Co-authors are Patricia Izar and
Eduardo Ottoni of the University of São Paulo, Elizabetta
Visalberghi of the Consiglio Nazionale delle Ricerche in Rome, and
Marino Gomes de Oliveira of the Fundacão BioBrasil in Bahia,
Brazil.
“One of the most significant things about this research is
that we see the behavior in an entire population and not in isolated
individuals,” says Fragaszy, who is considered one of the
world’s top experts on capuchin monkeys. “Also, it is
the first time this behavior has been observed in wild capuchins.”
Another study, published in the journal Science
at about the same time, also reports more generalized tool use among
capuchins, in a different area of Brazil.
Fragaszy and her colleagues first saw evidence of tool use for nut-cracking
among Brazilian capuchins in a photo essay published in the February
2003 issue of BBC Wildlife
magazine. The dramatic pictures showed the monkeys lifting improbably
large stones to crack palm nuts, which had been put in scoured “anvil”
areas that indicated long-term use. Fragaszy traveled to the area
in Brazil where the photographs were taken, not quite sure what
to expect. She soon she saw, from a blind built in front of a nut-cracking
site, monkeys coming to break open nuts with huge stones.
The study adds important new information to increasing knowledge
that human beings are not the only primates who use tools. At one
time, the use of tools was considered an important difference between
humans and other primates, but scientists some time ago discovered
that chimpanzees in the wild use tools in several ways.
“What we found is that these capuchins are extremely skilled
weightlifters,” says Fragaszy. “The video we took of
them cracking stones shows just how remarkable their ability to
lift these stones has become.”
A number of puzzles remain, and Fragaszy hopes to understand them
better after return visits to the site. First of all, some of the
cracking stones are large, water-smoothed rocks, which aren’t
found in the immediate area. Where do they come from? Have the monkeys
transported them over a very long time?
Just as perplexing is a high rocky ridge nearby, on top of which
are several anvil sites and the remains of hundreds of cracked palm
nuts. Just how the small monkeys managed to lug the heavy stones
to the top remains a mystery. There are, in fact, many such ridges
in the area with anvil sites.
The site is a biological reserve operated by the Fundacão
BioBrasil in a dry woodland habitat in northeastern Brazil. While
it has become an ecotourism site for its healthy and often remarkable
bird population, the discovery of tool-using capuchins at the site,
which is more than an hour’s drive on poor roads from the
nearest town, adds a new layer of scientific richness to the area.
Interestingly, the researchers observed monkeys using two forms
of action to crack nuts. In one, the monkey sat or stood bipedally,
held the stone in both hands and raised and lowered the stone with
arm and shoulder movements. A more strenuous method involves a monkey
rising quickly to a nearly vertical position by standing explosively
and raising the stone to shoulder height before crashing it down
on the nut.
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