Hormone treatment makes captive lions more manageable

As the extent of suitable habitat decreases and conflict with humans increases, many African lions end up being moved to sanctuaries where they can be cared for and protected. Add to this the lions rescued from circuses, foreign zoos and war zones, and it becomes apparent that significant numbers of lions need to be managed at such sanctuaries. This is not a simple task when dealing with a large apex predator that can be aggressive and territorial. 

Often lone lions are rescued and brought to a facility where other lions already live in groups. It is not healthy for lions to live alone as they are social animals with complex group structures and they thrive on close relationships with others. It would be ideal to introduce newcomer lions into established groups, but this is usually not possible due to the levels of aggression and intolerance towards outsiders.

In a rather novel approach, researchers from the University of Minnesota have been treating captive lions with the hormone oxytocin to determine whether this would make their behavior more prosocial and manageable. Oxytocin is known to enhance social bonding in some group-living mammals, such as meerkats, although most of the previous research on the effects of the hormone has been focused on bonded pairs of animals, such as marmosets, macaques and chimpanzees. The effects of oxytocin have never before been tested in a non-domesticated social group of carnivores, such as lions.

The current study took place during 2018 and 2019, on a wildlife reserve in Dinokeng, South Africa. Researchers, led by animal biologist Craig Packer and neuroscientist Sarah Heilbronner from the University of Minnesota, used hunks of raw meat to lure lions up to a fence so they could spray oxytocin up their noses with a modified squeeze-bottle. 

“By spraying the oxytocin directly up the nose, we know it can travel up the trigeminal nerve and the olfactory nerve straight up into the brain.” said study first author Jessica Burkhart. “Otherwise the blood-brain barrier could filter it out.”

After spraying 23 lions with oxytocin, Burkhart and her colleagues measured changes in aggressive behavior within the group and between groups. Their findings are published today in the journal iScience, where they describe the effects of the hormone on lion social behavior.  

“You can see their features soften immediately, they go from wrinkled and aggressive to this totally calm demeanor,” said Burkhart. “They totally chill out. It’s amazing.” 

The researchers found that a sprayed lion would allow other members of the group to approach more closely when it was in possession of a favorite toy. 

“After the lions were treated with oxytocin, and we gave them their favorite pumpkin toy to play with, we saw the average distance between them drop from about 7 meters with no treatment to about 3.5 meters after oxytocin was administered,” explained Burkhart.

This greater social tolerance was not seen when sprayed lions were in possession of food, however. But the hormone did lead to decreased vigilance and greater tolerance in the presence of potential intruders from another group. Recordings of the roars of other, unknown lions were played and, whereas untreated lions always roared back in response, lions treated with oxytocin never responded by roaring. This finding is important when considering possible approaches to the introduction of new lions into an established group.

In order to keep lions safe and away from humans, many have been transported to private fenced reserves, which often results in lions from different prides being mixed in with one another. In addition, when lone lions arrive at such sanctuaries they need to be integrated into existing groups and the oxytocin treatment may help facilitate this.

“Currently we’re working on introductions of animals who have been rescued from circuses or overseas or war zones that now live in sanctuaries,” said Burkhart. “The hope is that this will translate to animals being relocated in the wild, helping them to become more inclined to their new social environment so they’re more curious and less fearful, leading to more successful bonding.”

The study is published in the journal iScience.

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By Alison Bosman, Earth.com Staff Writer