Perhaps elephants are known for their memory because their very survival in our human-dominated world depends on it. This may be why elephants can recognize individual people by our voices.
Humans are the
most significant threat to elephants after lions, but not all humans pose the
same threats. New research published today in Proceedings of the National Academy of Sciences reports that
elephants’ memory is so good that they can distinguish the voices of different
human ethnic groups, as well as among humans of different sexes and ages.
There are two ethnic groups in Kenya that differ in terms of their
relationship with elephants. For young Maasai men, one of the ways in which
they demonstrate their strength and masculinity is by spearing elephants. The
Kamba, who are primarily farmers, represent little threat to elephants’
wellbeing.
In 2007, one
group of researchers discovered that elephants
are more fearful of the scent of Maasai men than Kamba men, and reacted
more aggressively to traditional Maasai garments than other types of clothing.
Now, Karen McComb
set out with her colleagues to see just how sophisticated the elephants’
abilities really are. It was known that elephants could use visual and
olfactory cues; could they also use auditory cues?
The main task for
any prey animal is to recognize and identify their predators and to assess the
level of threat imposed by those predators in order to determine the most
optimal outcome. For example, the best escape route for a monkey fleeing a
harpy eagle will be different from the best way to escape a stalking jaguar. It’s
no wonder that many animals have evolved different alarm calls to distinguish
between aerial predators and terrestrial predators.
Other animals
use even more complicated mechanisms to detect nearby predators. The
Galapagos iguana has evolved the ability to identify
the alarm calls of the Galapagos mockingbird, which that species uses to
communicate about nearby hawks. Without their eavesdropping skills, the iguanas
would never see an incoming attack until it was too late to avoid it. The Sahamalaza
sportive lemur of Madagascar uses a similar trick to avoid the raptors,
cats, and snakes that share its habitat.
While those
examples of threat assessment are impressive, they’re not very fine-grained.
Any aerial predator gets the same aerial predator alarm call, for example. If
you’re a howler monkey, that make sense: it’s better to be hyper-vigilant than
to risk meeting the business
end of a harpy eagle’s talon. The elephants’ distinction among the Maasai
and Kamba on the basis of scent and garment coloration is also fairly
large-grained
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But there’s far
more variation in human voices than in our natural body odors or the types of
clothing we wear. If elephants were able to distinguish among the Maasai and
the Kamba in terms of auditory features hidden in their voices, then that would
represent a far more sophisticated sort of reasoning.
McComb and her
group conducted almost 150 field playback experiments with 48 elephant groups
in Kenya’s Amboseli National Park. After playing the sound through their
loudspeakers, they recorded any defensive posturing or aggression as well as attentive behaviors such as listening or investigative sniffing.
The camouflaged setup for playback of vocal recordings. Image: Graeme Shannon, used with permission.
Their
first discovery matched the 2007 findings: elephants were more likely to react
defensively to the voices of Maasai males saying “look, look
over there,
a group of elephants is coming” in their language than to the voices of
Kamba males saying the same thing in their language.
But a second experiment was more surprising. When played the voices of Maasai
men and women, the elephants responded far more aggressively to the male
stimuli. That makes a good deal of sense, as Maasai women aren’t involved in
the elephant-spearing events that characterize Maasai culture.
However, when the researchers artificially modified the voices, making the male
voice sound female and vice versa, the responses were unchanged. In other
words, the elephants responded to the sex of the original speaker, rather than
the perceived sex of the resynthesized voice. That means that the elephants may
truly be aware of vocal features that are associated with human sex, such as
the females’ more “breathy” voices, rather than other correlated
variables, such as fundamental frequency. “Elephants do not appear to base
their sex distinction solely on the cues most commonly used by humans to
distinguish between the voices of the sexes,” McComb says.
In this video, an elephant herd reacts to the voice of a Maasai male.
Finally, the elephants also distinguished between the voices of Maasai men,
which pose a threat, from those of Maasai boys, which don’t.
“These findings provide unique evidence that a cognitively advanced social
mammal can use language and sex cues in human voices as a basis for assessing
predatory threat,” they write. “Given that humans are undoubtedly the
most dangerous and adaptable predator that elephants typically face, such
skills are highly adaptive and could prove crucial for survival.”
You might be tempted to argue that the elephants are actually marking a
distinction between the Maasai and Kamba languages, rather than the less
obvious acoustic distinctions in the voices themselves. That would actually be impressive by itself, but the fact that the elephants also notice sex and age
differences suggests a far more complex sort of skill
Indeed, these capabilities are far more sophisticated than the simple capacity to
distinguish between aerial and terrestrial predators, or between humans wearing
different types of clothing. Interestingly, the elephants’ behavioral reaction
to the perceived human threat was very different from the way they respond to playbacks
of lion roars. When played lion sounds, elephants typically react by mobbing,
which is an approach behavior that often proves effective in driving off the
predator. But mobbing would be a bad idea when facing a group of humans armed
with spears; instead of approaching, elephants retreat from humans.
Elephants aren’t the only species that can capitalize on nuanced features of
human behavior or culture. Bottlenose
dolphins in Brazil, for example, have learned to cooperate with human
fisherman, resulting in a bigger piscine bounty for each species. And wild
American crows can identify and remember individual human faces.
“Having the ability to discriminate real from apparent threat is therefore
highly adaptive,” for elephants, McComb writes, “particularly in the
case of human predators that differ in relatively subtle cues, and where the
associated danger is likely to show pronounced spatial and temporal variation
across the landscape.”
Hidden in her conclusion lies a message that should be impressive and also
slightly terrifying. It is remarkable that a species so different from ours has become so familiar
with us that they can respond to our voices with such specificity and nuance. And
yet it is equally heartbreaking that elephants have had enough experience with
human aggression that evolution has endowed them with that ability. If there’s a silver lining to be found, it’s that the elephants know that not all humans are to be feared.
McComb K., Shannon G., Sayialel K.N. & Moss C. (2014). Elephants can determine ethnicity, gender, and age from acoustic cues in human voices, Proceedings of the National Academy of Sciences.
Header image: Wikimedia Commons/Brian Snelson.
