Life is tough, if you're a lion. Male lions are always at risk of being killed by groups of rival males, or, if they're lucky, exiled from their prides. Females, meanwhile, always face the possibility of having their cubs killed when a new male coalition takes over their group.
A pride, which is the core social grouping of lion life, is made of a group of anywhere from two to twenty related females and their offspring, along with a coalition of one to nine males. While the males are usually related to each other, they're unrelated to the females. The females give birth at the same time and the cubs are nursed communally. Eventually, the males leave their groups and create their own coalitions, while the females usually stick around with their sisters, mothers, aunts, cousins, and grandmothers. Once they form a coalition, the males might try to acquire an existing pride by fighting with its resident males. If they win, the new coalition takes over, gains more territory, and usually kills off all the cubs. They can then begin mating with the pride's females. Now, it's their turn to protect their pride and territory from a hostile takeover.
In such an uncertain, often violent social world, how can lions maintain their friendships? One way, according to new findings published last week in the journal PLOS ONE, is by snuggling up to their pridemates.
Researchers observed the sorts of interactions among the captive lions at the Tama Zoological Park in Tokyo, Japan that might be characterized as friendly. Two of the most obvious affiliative behaviors that occur among lions are head rubbing and licking, and that's what the researchers decided to focus on.
Head rubbing is when one lion bends its head towards the head, neck, or most often, under the chin of a second lion, and nuzzles up against it. The behavior provides not only tactile stimulation, but it may also play a role in sensory communication. It isn't yet clear why, but lions often rub their heads on surfaces before scent-marking them with urine, suggesting that compounds that occur on their heads are somehow involved in olfactory communication. Licking has hygienic benefits, to be sure, but might also fulfill the same social purpose as grooming among primates and other mammals.
After their observations were compared with the genetic relatedness between individuals, their dominance hierarchy, and their spatial proximity, the researchers concluded that the best explanation for lion snuggling is that, rather than signifying submission or dominance, it establishes, maintains, and strengthens social bonds, just as allogrooming does among primates. Still, males and females expressed their affection differently.
Licking, for example, occurred between pairs of females nearly 97% of the time. The researchers interpret the sex difference as reflective of the maternal origins of licking behavior. That is, licking may be "originally adopted from the behavioural repertoire of maternal care." This would make licking among lionesses analogous to "contact swimming" among female dolphins. The behavior is primarily used by female dolphins to teach their calves how to swim, but may have become co-opted as a way to reinforce social bonds among females. If licking isn't usually kept in the male lions' social toolbox, then it stands to reason that they wouldn't often be seen using it. Faced with the never-ending prospect of having to contend with new males, it would be important for females to maintain their own relationships.
On the other hand, head rubbing was dominated by the males. While all lions engaged in head rubbing, the recipient of the behavior was most likely to be male.
The researchers explain that "in the wild, resident male coalitions engage in high-risk cooperative behaviors, [such as] territorial defense against nomadic male coalitions. Because the numerical odds against intruders is a good predictor of the outcome of a fight, larger coalitions can stay longer in a pride and can enjoy higher per capita reproductive success." Since males must always be ready to defend their pride from interlopers, it makes sense that they would constantly need to ensure close bonds with the other males in their coalitions. Having a tight-knit group makes the male coalition more likely to win a fight against a group of trespassers, and, in turn, this increases the probability that their cubs will survive to adulthood.
All the usual caveats that apply to studies of captive animal behavior apply here as well. In zoos and sanctuaries, lions are able to spend more of their time in social interactions than in the wild, since they don't have to spend their time finding their next meal. Since their enclosures are by definition smaller than their wild counterparts' typical territory size, captive lions spend more time in close proximity to each other. Taken together, the absence of competition over food sources combined with their reduced physical distance means that captive prides don't precisely replicate the fission-fusion dynamics that characterize wild lion sociality.
Still, this research suggests that cuddles are more than just cheerful or friendly interactions. No, they're far more tactical. Lion snuggles betray evidence of the often brutal life facing lions on the savannah. Indeed, for a lion death is always around the corner. And the best safeguard against death is having good friends.
Matoba T., Kutsukake N. & Hasegawa T. (2013). Head Rubbing and Licking Reinforce Social Bonds in a Group of Captive African Lions, Panthera leo, PLOS ONE, 8 (9) e73044. DOI: 10.1371/journal.pone.0073044
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Both photos via Matoba et al., (2013).