Last December an Instagram Reel of a “crying” bison—created by photographer Chris Henry—went viral. The video has received more than eight million views and generated thousands of comments. But can bison really be sad? Do nonhuman animals ever cry from sadness?
Tears are useful for our eyes—as they are for many other animals. A lot of mammals, reptiles and birds have tear glands that secrete aqueous fluid. The precise concentrations of biochemical components of tears differ between species and have evolved as adaptations to different environments.
Tears come in three recognized types. Basal tears provide basic maintenance. Glands spontaneously release these tears to deposit a protective nourishing film on the cornea.
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Then there are reflex tears, which are produced in response to an external stimulus, such as irritation or injury to the eye. These also spring up after exposure to cold or certain substances, such as the chemicals released by freshly chopped onions. Reflex tears cleanse the eyes and can help heal damage.
The third form consists of emotional tears, which are prompted by one’s mental state. Societies have long seen sobs of sadness as a uniquely human behavior—so much so that some communities believed the ability to produce emotional tears could be used as a test of whether someone was secretly a witch or werewolf.
Although its exact function is unknown, there are many hypotheses for why we weep. A good cry may help us cope with challenges by signaling our emotional pain, distress or vulnerability. Our tears can affect the people around us, strengthening social relationships, encouraging cooperative behavior and inhibiting aggression or eliciting care, help or protection.
Today scientific consensus is that emotional tears are indeed uniquely human. But a small amount of evidence hints at some similar occurrences in other animals and has prompted interest from researchers. As one example, even though it is not beneficial for many adult animals to broadcast weakness, many young animals cry without tears to signal their mother. And young deer produce a secretion during stress and hunger from a gland just below the eye to which their mother responds. That same gland is used by adult deer to release scents into the environment.
There are also anecdotes about nonhuman animals that have seemed to be weeping in sadness, including stories of elephants, a sad gorilla and wolves that had become exhausted and fallen behind in the pack. But science has not backed up these stories. For example, in a systematic survey on the subject, published in 1985, people who worked professionally with animals, including veterinarians and zookeepers, reported no observations of an animal crying emotionally.
More recent investigations offer greater nuance. In a study published in 2022, researchers looked at moist or watery eyes in dogs, a phenomenon familiar to anyone who has ever had a puppy. They found that canines secrete tears during a seemingly positive emotional situation: when reuniting with their owner. The hormone oxytocin, which supports bonding, triggers this response. That reaction is something humans notice and appreciate, the study further found. When presented with photographs of dogs, people reported being more eager to care for the pooches with tears in their eyes (something the scientists who took the photographs had produced with saline drops) than for dogs with dryer eyes. Dogs have evolved over the generations to communicate with our species through eye contact. It’s possible that they tear up because doing so prompts love and protection from humans; it may even strengthen bonds between us and them.
Researchers have also documented domestic pigs tearing up in poor farm conditions, specifically with increased red staining below the eyes. This fluid is not a true watery tear but rather a secretion of the Harderian gland, something present in many species—though in humans specifically it is poorly developed. In pigs these secretions are also produced by stress. These animals show more staining when they also have lower heart rate variability—another physiological marker of stress—and signs of reduced well-being, such as a bitten-off tail or a display of fear when humans approach. Rats demonstrate the same phenomenon, which is sometimes called “blood tears” because it leaves rust-colored trails in and under the inner corner of the eye. In these rodents, the response increases with environmental stress. It also relates to age and overall well-being—though further study is needed to understand those links.
So what should we make of the “crying bison” video? Though we cannot say that the bison isn’t sad, it’s more probable that people are anthropomorphizing this unknowing Instagram star—that is, people are attributing human behaviors and characteristics to a nonhuman animal.
Indeed, in a study that presented people with portraits of five different animal species—cats, dogs, horses, chimpanzees and hamsters—people saw images in which tears were added as depicting “sadness,” just as it would in humans. In fact, photoshopped tears made these animals seem “less aggressive” and “kinder” to the study participants. People also reported that those animals showed “higher emotional intensity.”
We find it extraordinary that a nonhuman animal could be shedding tears in part because we expect that to be a human act—and, in response, we have the urge to respond emotionally to that creature. As to the bull in the video, the Instagram caption suggests he lives free in the wild on the plains of Utah. He appears to be in peak condition and is breathing calmly. He shows no other indication of stress. He stands quietly, watching. It’s probable that he had a speck of dust in his eye or the wind had irritated him.
To date, there has been no evidence that suggests bison exhibit emotional crying. That said, more than 20,000 years ago someone painted a bison in the French cave of Chauvet that, some contend, has tears falling from its eyes in a precursor to today’s Internet sensation.
This article originally appeared in Eos and was reproduced with permission.