Scientific American 201906

ADVANCES

18 Scientific American, June 2019

ANIMAL BEHAVIOR

Monkey

Alarms

Some prey species send warning

calls to scare off predators

Anthropologist Dara Adams was follow-
ing a troop of six saki monkeys in Peru’s
Amazon rain forest, when out of nowhere
they began shrieking, hooting and barking
loudly. Suddenly, sleek and black as night,
a small wildcat called a jaguarundi
descended the trunk of a Brazil nut tree,
leaped to the forest floor and ran off into
the jungle.
Many animals use alarm calls to warn
others in their species about a predator.
But that does not entirely explain what
Adams saw—because the monkeys con-
tinued calling even after the entire group
became aware of the threat. A more tanta-
lizing possibility is that the monkeys were
addressing the cat itself, blowing its cover
and warning it to call off the hunt.
This idea, which scientists call the “pur-
suit deterrence hypothesis,” has been pro-
posed in studies of birds, fish and mam-
mals. But the vast majority of studies focus
on the calling prey animal, rather than the
impacts of those calls on the predators,
Adams says. So she and her team from the
Ohio State University decided to radio-col-
lar two ocelots, another type of petite cat
found in the Peruvian Amazon. While
tracking the cats’ movements, Adams and
her colleagues used an unobtrusive loud-
speaker to broadcast recorded alarm calls
from titi and saki monkeys, two species
ocelots prey on. They also played other
types of social calls made by the monkeys.
The alarm calls proved an effective
deterrent, prompting the ocelots to move
away from the loudspeaker. When the cats
heard the other types of calls, they either
stayed still or moved in some random
direction—but never as far away as when
they heard the alarm ones, the team
reported last November in Animal Behav-
iour. “Our study provides the first experi-
mental evidence to show that wild ambush
predators in natural conditions are de -
terred by prey alarm calls,” Adams says.
Dan Blumstein, a biologist at the Uni-

versity of California, Los Angeles, who was

not involved in the study, agrees that the

findings suggest these monkeys’ calls serve

to warn off the cats. But he wonders, “Are

they moving away out of fear of getting

attacked by the monkeys? Or are they

moving away because they know the

game is up?” — Jason G. Goldman

1

2

Toppin’s titi monkey ( Callicebus toppini ) ( 1 ) and ocelot ( Leopardus pardalis ) ( 2 ).

JASON G. GOLDMAN

(^1 ); HAL BERAL

Getty Images

(^2 )