10 | New Scientist | 1 June 2019
HOW do you teach a monkey new
tricks? Labs have proved difficult
places to train monkeys to respond
to different sounds, but in the
forests of Senegal’s Niokolo-Koba
National Park, researchers were
astonished how quickly one
species of monkey adapted
its behaviour to a new sound.
Julia Fischer at the German
Primate Center in Göttingen
and her team flew drones over
a community of green monkeys
(Chlorocebus sabaeus) in the area,
to see what they made of a new
flying object in their environment.
They responded instantly, making
alarm calls to warn one another
of the potential new threat.
The vocalisations were
distinct from the ones they made
in response to models of leopards
and snakes, but almost identical to
calls made by a related species of
monkey about eagles. The results
suggest a hardwired response to
the perception of an aerial threat
and the use of that specific call.
The monkeys adapted so
quickly to the mechanical noise
that they began scanning the
skies and making the calls evenwhen the sound of the drone
was played from the ground. The
monkeys were never seen issuing
alarm calls in response to birds of
prey in the area, suggesting that
the birds they usually see aren’t
considered a threat. The drones,
however, seemed to be perceived
as dangerous.
“It’s certainly disconcerting,
unpredictable, something they’venot seen before, so it makes sense
to alert everybody,” says Fischer.
She says she was “blown away”
by how rapidly the monkeys
appeared to learn. “The listeners
are smart. It’s almost impossible
to get a monkey in a lab to do an
audio task.” It isn’t clear why
such learning is harder in a
lab environment, she says.
The study involved a year’s
worth of fieldwork by a team of
eight, who flew the drone about
60 metres above the monkeys.
The research wasn’t without
incident. Fischer had to duckinside a shelter made of palm
leaves at one point, after a baboon
ran to attack the leopard model
she was holding.
Vervet monkeys (Chlorocebus
pygerythrus) in East Africa are
related to green monkeys. They
have been closely studied for
the different calls they make in
response to a variety of predators,
including pythons, leopards,
baboons and martial eagles.
The expectation for the green
monkey study was that they would
stay silent, come up with a new
alarm call or produce one similar
to the vervet monkeys’ eagle call.
Fischer’s bet was on the eagle call
option, and she was proved right.
The vocalisation appears to be
highly conserved by evolution
(Nature Ecology and Evolution,
doi. org/c6db).
“It teaches us about
how different their vocal
communication system is from
ours,” says Fischer. “There is a
very limited level of flexibility.” ❚A START-UP is deliberately trying
to crash aircraft into drones to test
a new collision-avoidance system.
US firm Iris Automation’s
technology for drones can detect,
identify and react to airborne
objects. The start-up says the
system can spot light aircraft from
500 metres away and respond in a
fifth of a second, and that it works
with the drone travelling at up to
210 kilometres per hour.Conventionally, collision-
avoidance systems for drones have
been similar to those used in other
aircraft, which rely on radar, so
are large and expensive. Instead,
the new system uses a single small
camera and artificial intelligence to
pick out objects that the drone could
collide with. When it detects one,
the drone drops by 50 metres,
cuts its speed and starts circling.
To test the system, the start-up
has set drones on a collision course
with helicopters and other aircraft
more than 7000 times, but has
had no crashes as yet. “We have
flown aircraft from many differentdirections and trajectories,” says
Alex Harmsen at Iris Automation.
Companies like Amazon and
Google may soon launch drone
delivery services. Both firms have
run or are running limited trials.
Harmsen says some customers
are close to obtaining licences for
trials in the US, with approvals
expected in the next two months.However, for the services to
go mainstream, there will have
to be little risk of a collision. Iris
Automation’s system will probably
be one of many to enable operation
in shared airspace, says Gary
Mortimer of sUAS News, an
industry drone website.
He thinks they could open up
the potential for widespread drone
use, beyond delivering parcels and
medical supplies. The systems
could be used by the emergency
services and for search and
rescue, agriculture and power-
line inspection, says Mortimer. ❚
David Hambling...while drones see
aircraft, and try to
collide with themAviation“The monkeys may be
hardwired to use this
call to warn each other
of aerial threats”Monkeys see drones...
Green monkeys make special calls to warn of aerial threat
PrimatesAdam VaughanIMAGE
BR
OKER
/ALAMY^ STOCK
PHOT
ONews
Wild green monkeys
rapidly adopted a
new alarm call7000
The number of times drones
were flown at aircraft in tests