African lions are extraordinarily social with the members of their own pride but violently, even deadly antisocial when it comes to outsiders. The cats are constantly on guard for what Craig Packer, a leading lion expert, has called “the dreadful enemy”—other lions seeking to take their territory and sometimes their lives. This lifestyle of teamwork and warfare has evolved to best exploit resources in the savannah. But lions’ space is shrinking dramatically, and many of the cats may need to build better relations with their neighbors. So Packer’s University of Minnesota colleague, neuroscientist Jessica Burkhart, wondered, would administering a hormone associated with emotional bonding serve as a social lubricant to cool tempers of the ultimate apex predator?
The beginnings of an answer emerged in a study published today in iScience. Lead author Burkhart and colleagues found that giving the cats spritzes of oxytocin, a hormone key to social and relationship cues in many species, can help make lions more friendly to strangers of their own kind. Oxytocin appears to utilize neural pathways of curiosity and social recognition so that meetings with outsiders, whether in captivity or the continent’s game reserves, might promise more detente and less death.
Most of the world’s felines are solitary animals. Lions, on the other hand, are uniquely social. The cats live in prides presided over by a handful of related females who share the duties of raising young, and hunting a hereditary territory stretching dozens or even hundreds of square miles in size. A few resident males also attend the group, mating, guarding and lying about as lions frequently do.
But lion social life is far from harmonious. It’s often defined by violent, even fatal, clashes that occur when several usurping males, themselves socially bonded, try to take over a pride, and its prime feeding territory, for themselves. When successful, the male lions will even kill the young of their predecessors to bring the females into heat to rear their own offspring. Because of this dynamic, lions are not only wary of outsiders but are often positively hostile.
Burkhart is exploring the brain science behinds lions’ unique social behavior. “The level of tolerance and the desire to either fight someone off or be close to them comes from neurochemistry,” she explains. “What is it that’s different in lions’ brains, as opposed to say tigers, who mate and then don’t want to see another tiger.”
That question led Burkhart to look at the way one particular hormone might impact lions’ brains, and thus their behavior. Oxytocin, sometimes dubbed 'the love hormone,’ is associated with childbirth and maternal bonding, and has been noted to play a role in social cues and relationships of various species. Studies have shown that oxytocin affects bonding between dogs and humans and promotes sexual partnerships among prairie voles. The hormone may also make meerkats even more social, and encourage humans to think and act for the benefit of a larger social group.
During the summers of 2018 and 2019, Burkhart and colleagues administered oxytocin to 23 captive lions on a wildlife reserve in Dinokeng, South Africa. Delivering a dose of oxytocin to a 400-pound lion was tricky, as one might expect. Protected by a strong fence, scientists lured the big cats close by offering them chunks of raw meat. When the lions approached to feed, the researchers used an atomizer, which resembles an old-fashioned spray perfume bottle, to deliver a dose of oxytocin directly up the lion’s nostrils—where it had a direct route to the brain via the olfactory nerve.
The dose, despite a very modest size, took effect in short order, “If I spray an aggressive lion, by the seventh squirt their demeanor completely changes. They are chilling out. They are blinking a lot which lions do when they are chilling,” she says. “We always wait 45 minutes just to make sure it’s taking effect, but in my opinion it seems to kick in within a few minutes.”
Burkhart’s team devised three tests to see how the hormone impacted behaviors among the lions who lived together in a group and how it influenced their behavior when confronted by strange lions from the outside. First they gave the lions a toy, in this case a pumpkin, and watched their behavior. The lions that had been exposed to oxytocin stayed closer together when playing with the object, and in close proximity they more often played with and groomed each other.
The researchers also tested how lions would react when presented with a single, high value food object, a frozen blood popsicle that wasn’t big enough to share. In this case, even when given oxytocin, the first lion to get the food typically became possessive and prevented its companions from approaching too closely—typically by growling and snarling. This result is a reminder that oxytocin’s effects aren't universal, but context specific and ripe for further study. Food conflict may be rooted in an entirely different kind of aggression, the authors suggest, or more natural feeding on larger items, like an animal carcass, could promote sharing and ease conflict.
In the third test, Burkhart’s group played recorded roars from unknown lions to a pride. In the wild, lions remain on guard for intruders, keeping out a sharp eye and even a keen ear. The cats roar to assert ownership of territory. When Burkhart’s group played roars meant to mimic challenges from unknown lions, the oxytocin-dosed cats never responded. But the strange roars always elicited a response from the control group. The oxytocin-dosed cats also behaved in a more relaxed and less on-guard way, and gathered closer together, while hearing the sounds of strange roars. The lions’ reaction to strangers may prove the most important result because of its potential value as a future conservation tool—lions that are less hostile to one another could more easily share space, whether in captivity or game reserves.
“I really like this study,” says Kelly Robinson, who has studied oxytocin in wild grey seals and shown that manipulating the hormone can drive positive social behaviors. “There has been lots of evidence to show if you manipulate oxytocin you do see prosocial changes. Researchers have asked for years if it might be possible to actually regulate aggressive behavior in captive carnivores in situations when they have to be put together. It’s great to see that someone has actually gone and done it. It makes complete sense to see if this can be something in the toolbox they can use to get carnivores to cohabitate more peacefully.”
Oxytocin’s possible use to promote friendly encounters holds promise for captive lions, who might trade unnatural and unhealthy isolation for shared spaces with sociable new companions. The impact might also be great among the continent’s remaining wild lion populations. Though only about half as many lions live now as a quarter-century ago, the space they have is shrinking fast. Today wild lions frequently live in reserves fenced not only to keep the animals in, but even more so to stop humans from encroaching further into the spaces. Lions living in such refuges aren’t able to disperse naturally, so maintaining physically and genetically healthy populations requires that wildlife managers frequently tranquilize lions and swap them between reserves. That process leads to a lot of meetings between strange lions, which sometimes simply don’t go well. In some preliminary tests, the hormone seems to help.
As part of ongoing research Burkhart has used oxytocin to help introduce strange lions in captive facilities. One pair was so aggressive to one another, over a period of months, that a fence separating them had to be repeatedly reinforced. After three weeks of carefully monitored oxytocin treatments, researchers were able to open a gate and put the pair together. “It totally changed everything, because it decreases the fear and a lot of times that’s a big part of the aggression,” she says. “And it makes them more inclined to have that social interest.”
Researchers still have many questions about the effects of oxytocin on lions. Animal social dynamics are complex and the results don’t predict how oxytocin might influence lion behavior in any number of situations. Robinson notes that studies with chimps have shown that context is crucial. Oxytocin does tend to increase prosocial activity within a group, but can also increase hostility towards outgroup members depending on the situation. “That’s definitely something that needs to be further explored where you are trying to take individuals from different places and put them together,” she notes.
Robinson says scientists also need to consider other questions about the treatment. “What are the consequences of giving elevated oxytocin levels to individuals for long term behavior? How long is it going to last and how consistently can you dose animals if it doesn’t last that long?” she asks. “All these things have to be worked out, but that doesn’t mean they can’t be worked out.”
The realities of wildlife management in an increasingly anthropogenic world might make such efforts a necessity. Even wild lions will often live on contained reserves, and humans will need to manage and commingle their populations. If oxytocin isn’t a panacea, Burkhart is hoping that continued efforts with the hormone will lead lions to be more accepting of strangers. “If you dose them right before they wake up in a new environment, their first impression is that they are inclined to be more socially curious, and less vigilant. So they are gonna be more open to that neighbor that you’re putting them next to.”