Researchers working at the Ozouga Chimpanzee Project in Gabon have observed
chimpanzees applying insects to the wounds of themselves and others,
something they say nobody has ever seen before. The observation could be
evidence of self-medication in the animals.
The Ozouga project is located in Loango National Park in Gabon, a patchwork
of thick forest, savanna, and coast home to a troop of about 45 chimpanzees
that scientists have watched and studied for years. But in November 2019,
volunteer Alessandra Mascaro saw something nobody with the project had ever
seen before.
Mascaro was filming the Ozouga chimpanzees, particularly one named Suzee. As
she watched, Suzee approached her adolescent son, Sia, who had an open wound
on one of his feet. Suzee looked at the wound then, suddenly, seemed to take
something out of her mouth and apply it to the injury. Reviewing the footage
later, it seemed to be something Suzee had grabbed from nearby. This was
strange and Mascaro showed the video back to the rest of the scientists. The
team decided to keep watch and soon saw it happen again with different
chimps. Based on the footage, the mystery object seemed to be some sort of
small insect.
In fact, over the course of 15 months, they saw this happen a total of 22
times -- 19 with animals tending to their own wounds (often bites from
scraps between group members or with outsiders), and three times with one
chimp tending to another's. In each, the chimps seemed to start by catching
an insect, crushing or holding it between their lips, then rubbing it on the
wound, sometimes multiple times. The researchers shared their findings today
in the journal Current Biology.
This behavior looked a lot like what scientists call self-medication. Many
animals are known to self-medicate. Wild red and green macaws eat clay to
help digestion. Pregnant elephants may eat certain leaves to induce
delivery. Birds may ward off parasites by weaving herbs (or cigarette butts)
into their nests, and orangutans have been seen rubbing an ointment made
from leaves and saliva onto their skin. But the Ozouga scientists say
nobody's ever seen animals self-medicate with an insect to treat an open
wound before.
"It's a really interesting set of observations," said Michael Huffman, a
primatologist with Kyoto University in Japan and an expert in animal
self-medication. "There's enough observations that they've made to show that
it's not a one-off thing." Huffman was not involved in the project, but he
was one of the scientists who reviewed the paper during the publication
process.
"It's delightful to find something new like this," said Richard Wrangham, a
biological anthropologist and primatologist with Harvard University and
founder of the Kibale Chimpanzee Project in Uganda. He said he was
particularly surprised at the use of insects as well as the episodes of one
chimp treating another.
However, there's one big caveat to this whole story: The scientists haven't
been able to identify the insects involved. Whatever they are seem very
small, maybe only a few millimeters in size, and the chimps don't leave a
lot of remains behind.
"Without information about that, we can't begin to look into the possible
function of that insect," said Huffman. "That's one thing that's still
missing." Also, to definitively prove that this is an act of
self-medication, Huffman said, the scientists would need to show that the
insects really do have some sort of healing or other positive effect, though
doing this in the wild may be difficult.
That said, it's not an outlandish idea that a bug may help the chimps soothe
pain or fight off infection. "There are studies showing that, in many insect
species, they have substances that help you," said Simone Pika, a cognitive
biologist with Osnabrück University in Germany and one of the leaders of the
Ozouga project.
Unfortunately, it's not easy to grab a half-chewed insect from a
chimpanzee's wound. Instead, Pika says, they've talked to entomologists and
come up with a couple of plans for tracking down the insect's identity. One
idea is to start by doing an insect inventory for the region -- a kind of
lineup of possible suspects -- and then trying to narrow things down from
there. Another is to wait to see the wound-tending behavior happen again,
and then, once the chimps have left the area, set up a perimeter around the
site, "then really turn every leaf to maybe find some of the insect
remains," said Pika.
Huffman noted that he wouldn't be surprised if more people started reporting
this kind of behavior now that the paper's published. "It is usually the
case when someone says, 'This is what I've seen' that everyone says, 'Oh,
I've seen the same thing.' And then people will have their radars on to that
in the future," he said.
Wrangham, however, suspects that the fact that it hasn't been reported
before means it may be unique to Ozouga. "It's probably a specific tradition
-- cultural tradition, socially learned tradition -- in this particular
population."
Wrangham did note that scientists where he works at the Kibale National Park
have spotted chimpanzees dabbing at wounds with leaves, another tradition
seemingly unique to just that one area. Though in that case they don't seem
to be selecting for a particular species of leaf, just grabbing what's
nearby.
And at both sites, scientists have seen one chimp caring for another. How
much animals engage in what's called prosocial behavior -- acting to benefit
another individual with no benefit to yourself -- is a hotly discussed
topic, and the three observations of one Ozouga chimp helping another may
become an interesting talking point in that discussion.
Reference:
Alessandra Mascaro et. al, Application of insects to wounds of self and
others by chimpanzees in the wild DOI: 10.1016/j.cub.2021.12.045
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Plants & Animals