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
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.