McEvoy should focus on the empirical (or falsifiable) basis of all this, and
Helm should consider the interesting reference to the different breeds of dogs
that prairie dogs can recognize. I loved the professor's comment that the
prairie dog's alarm call for the hawk "is so brief -- but then hawks _are_ fast
critters").
In the 1990s, inspired in part by Slobodchikoff’s studies, the primatologist
Klaus Zuberbühler began investigating monkey vocalizations in the dense and
cacophonous forests of the Ivory Coast in Africa.
Over the years, he and his colleagues discovered that adult male Campbell’s
monkeys change the meaning of their screeches by combining distinct calls in
specific sequences, adding or omitting an “oo” suffix.
Krak exclusively warns of a leopard, but krak-oo is a generalized alarm call.
Iolated pairs of booms are a “Come this way!” command, but booms preceding
krak-oos denote falling tree branches.
Studies of songbirds have also uncovered similar complexity in their
communication.
Japanese great tits, for example, tell one another to scan for danger using one
string of chirps and a different set of notes to encourage others to move
closer to the caller.
When researchers played the warning followed by the invitation, the birds
combined the commands, approaching the speaker only after cautiously surveying
the area.
In the South Pacific, biologists have shown that humpback-whale songs are
neither random nor innate: rather, migrating pods of humpback whales learn one
another’s songs, which evolve over time and spread through the ocean in waves
of “cultural revolution.”
And baby bottlenose dolphins develop “signature whistles” that serve as their
names in a kind of roll call among kin.
With the help of human tutors, some captive animals have developed especially
impressive linguistic prowess.
Dolphins have learned to mimic computer-generated whistles and use them as
labels for objects like hoops and balls.
A bonobo known as Kanzi communicates with a touch-screen displaying hundreds of
lexigrams, occasionally combining the symbols with hand gestures to form simple
phrases.
And over the course of a 30-year research project, an African gray parrot named
Alex learned to identify seven colors, five shapes, quantities up to eight and
more than 50 objects.
He could correctly pick out the number of, for instance, green wooden blocks on
a tray with more than a dozen objects; he routinely said “no,” “come here” and
“wanna go X” to get what he desired; and on occasion he spontaneously combined
words from his growing vocabulary into descriptive phrases, like “yummy bread”
for cake.
Slobodchikoff’s studies on prairie dogs have long hovered on the periphery of
this burgeoning field.
Unknown to Slobodchikoff, around the same time that he began recording
prairie-dog alarm calls in Flagstaff, Peter Marler, the renowned
animal-communication expert and one of Slobodchikoff’s former professors, was
working on a similar study, one that would eventually redefine the field.
In the spring of 1977, Marler sent Robert Seyfarth and Dorothy Cheney — a
husband-and-wife duo of primate scientists — to Amboseli, Kenya, to study the
alarm calls of small silver-haired monkeys known as vervets.
Earlier research had hinted that vervet monkeys produced different vocal
warnings for different predators: a kind of bark to warn of a leopard; a
low-pitched staccato rraup for a martial eagle; and a high-pitched chutter for
a python.
Seyfarth and Cheney decided to further investigate these findings in a
controlled field experiment.
The two scientists hid a loudspeaker in the bushes near different groups of
vervets and played recordings of their alarm calls, documenting the monkeys’
responses.
Even in the absence of actual predators, the recordings evoked the appropriate
escape strategies.
Leopard-alarm calls sent monkeys scampering into the trees.
When they heard eagle-alarm calls, they looked up and took cover in the bushes.
In response to the warning for snakes, the primates reared up on their hind
legs and scanned the ground.
Contrary to the consensus of the time, the researchers argued that the sounds
animals made were not always involuntary expressions of physiological states,
like pain, hunger or excitement.
Instead, some animals systematically used sounds as symbols.
In both the kryptotechnic Peirceian academia that Grice abhors (but embraces)
and the popular press, vervet monkeys became celebrated mascots for the
language-like abilities of animals.
While the vervet research won acclaim, Slobodchikoff’s remained frustratingly
sidelined.
Marler, Seyfarth and Cheney worked for the well-staffed and moneyed Rockefeller
University in New York.
Slobodchikoff conducted his studies on a shoestring budget, compiling funds
from the university’s biology department, very occasional grants and his own
bank account.
Slobodchikoff did not collect enough data to formally present his research at a
conference until 1986.
And it was not until 2006 that he published a study with the same kind of
playback techniques that Cheney and Seyfarth used in Kenya, which are essential
to demonstrating that an animal comprehends and exploits the variation in its
calls.
Although many scientists attended Slobodchikoff’s talks at conferences and
spoke with him about his research in private, they rarely referenced his
studies when publishing their own.
And despite a few news stories and nature documentaries, prairie dogs have not
secured a seat in public consciousness as a cognitively interesting species.
It did not take long for Slobodchikoff to master the basic vocabulary of
Flagstaff’s native prairie dogs.
Prairie-dog alarm calls are the vocal equivalent of wartime telegrams: concise,
abrupt, stripped to essentials.
On a typical research day, Slobodchikoff and three or four volunteers visited
one of six prairie-dog colonies they had selected for observation in and around
Flagstaff.
They usually arrived in the predawn hours, before the creatures emerged from
their slumber, and climbed into one of the observation towers they had
constructed on the colonies: stilted plywood platforms 10 feet high, covered by
tarps or burlap sacks with small openings for microphones and cameras.
By waiting, watching and recording, Slobodchikoff soon learned to discriminate
between “Hawk!” “Human!” and so on — a talent that he says anyone can develop
with practice. And when he mapped out his recordings as sonograms, he could see
clear distinctions in wavelength and amplitude among the different calls.
He also discovered consistent variations in how prairie dogs use their alarm
calls to evade predators. When a human appeared, the first prairie dog to spot
the intruder gave a sequence of barks, which sent a majority of clan members
scurrying underground.
When a hawk swooped into view, one or a few prairies dogs each gave a single
bark and any animal in the flight path raced back to the burrow.
Slobodchikoff argues that, because of a hawk’s speed, there’s little time for a
more complex call.
The presence of a coyote inspired a chorus of alarm calls throughout the colony
as prairie dogs ran to the lips of their burrows and waited to see what the
canine would do next.
When confronted with a domestic dog, however, prairie dogs stood upright
wherever they were, squeaking and watching, presumably because tame, leashed
dogs were generally, though not always, harmless.
Something in Slobodchikoff’s data troubled him, however.
There was too much variation in the acoustic structure of alarm calls, much
more than would be expected if their only purpose was to distinguish between
types of predator.
Slobodchikoff arranged for various dogs — a husky, a golden retriever, a
Dalmatian and a cocker spaniel — to wander through a prairie-dog colony one at
a time.
The recorded alarm calls were still highly variable, even though the intruders
all belonged to the same predator class.
"That led me to think, What if they are actually describing physical features?”
Slobodchikoff remembers.
What if, instead of barking out nouns, prairie dogs were forming something
closer to descriptive phrases?
To find out, he became a participant in his own experiment.
Slobodchikoff and three colleagues paraded through two prairie-dog colonies
dressed in either jeans and white lab coats, or jeans and variously colored
shirts: blue, gray, orange, green.
The prairie dogs produced highly similar alarm calls for each person in the lab
coat, except for one especially short researcher.
But they chirped in very different ways for most of the different colored
shirts.
In a related experiment, three slender women differing in height by just a bit
meandered through a prairie-dog habitat dressed identically except for the
color of their T-shirts.
Again the animals varied their calls.
And in another study, prairie dogs changed the rate of their chirping to
reflect the speed of an approaching human.
If prairie dogs had sounds for color and speed, Slobodchikoff wondered, what
else could they articulate?
This time, he and his colleagues designed a more elaborate test.
First they built plywood silhouettes of a coyote and a skunk, as well as a
plywood oval (to confront the prairie dogs with something foreign), and painted
the three shapes black.
Then they strung a nylon cord between a tree and an observation tower, attached
the plywood figures to slotted wheels on the cord and pulled them across the
colony like pieces of laundry.
Despite their lack of familiarity with these props, the prairie dogs did not
respond to the cutouts with a single generalized “unknown threat” call.
Rather, their warnings differed depending on the attributes of the object.
They unanimously produced one alarm call for the coyote silhouette; a distinct
warning for the skunk; and a third, entirely novel call for the oval.
And in a follow-up study, prairie dogs consistently barked in distinct ways at
small and large cardboard squares strung above the colony.
Instead of relying on a fixed repertory of alarm calls, they were modifying
their exclamations in the moment to create something new — a hallmark of
language Hockett calls “productivity.”
By the late 1990s, Slobodchikoff had transitioned from studying paper sonograms
to generating computer-based statistical analyses of the frequency, duration
and harmonic structure of prairie-dog vocalizations.
Based on such analyses, he said that the most crucial distinctions between
prairie dogs’ calls are not in length or the number of discrete chirps but
rather in the amplitudes of overlapping sound waves in each call — the
composite of which is essentially their tone.
Cheers,
Speranza
