Human parents will instinctively respond to the cries of their child, so it is not so strange that other animals behave the same way toward their offspring. However, the distress call of a newborn fawn can also have the same effect on us, despite it being a member of a different species. It is something that we as humans like to attribute to our unique emphatic nature, but scientists recently discovered that some deer will also show the same protective tendencies toward human infants. These findings were the result of a study by researchers into interactions between mule deer and their white-tailed cousins.
“Our results suggest that animals can be sensitive and show behavioral responses to newborn distress vocalizations of diverse species without proposing a special human capacity for empathy, a recent history of association, or a close taxonomic relationship,” wrote researchers in a recent edition of The American Naturalist.
Instead of possessing the human capacity for empathy, researchers believe this response in deer is due mainly to “altruistic” instincts. The study first focused on the differences between the response of mule and whitetail deer to their own young. Both species respond to the calls of a distressed fawn, but whitetail does will verify whether the fawn is their own before acting defensively. In contrast, mule deer mothers will protect even a whitetail fawn. Scientists soon discovered that the does’ responses were not limited to just similar species, but also the cries of infant humans, marmots, and seals, as well.
In their experiment, University of Winnipeg biologist Susan Lingle and Midwestern University researcher Tobias Riede set up speakers in prairies near an Alberta ranch. When playing the distress cries of young mammals, scientists discovered that mule deer moved quickly towards the speakers. Deer that approached within 10 meters of the speaker also displayed some form of protective behavior, such as leaning towards the device or hopping around it with ears held to the side and fur flared. Other noises, such as birdsong or coyote sounds, either drove the deer away or elicited no reaction.
Lingle and Riede believe that as long as an animal’s “distress call” falls within the same pitch as that put out by their own kind, mule deer does will respond as if it is their own fawn. It is likely that mule deer developed this trait not to protect other animals, but to respond more quickly to their offspring in times of crisis.
“These are calls that are generally made in a life-or-death situation,” Lingle told New Scientist. “I think the advantage of securing survival for your offspring outweighs the potential for error.”
Researchers believe that deer are part of a large group of mammalian mothers that are attuned to the distress calls of other species. Some, like whitetail deer, merely investigate and move off. Others, such as humans and some canines, will even aid and protect crying infants. Lingle said that animal altruism is still a major mystery in evolutionary biology, especially in mule deer.
“This line of research may bring insight into mechanisms underlying interspecific relationships, for it suggests that nonhuman animals are sensitive to cues associated with infants even when those cues are present in different species,” the researchers concluded.