"Friendly" hyenas more likely to engage in mobbing behavior

After more than three and a half decades of diligent observation, researchers at Michigan State University (MSU) are unraveling some of the enigmatic behaviors of a unique type of mob – those comprised of spotted hyenas.

The findings of this research, published in the journal Proceedings of the Royal Society B, shed light on the intricate relationships and social interactions among hyenas, which influence their decisions to join forces and confront lions cooperatively, a behavior known as mobbing.

Mobbing behavior 

Lead author Tracy Montgomery initiated this project during her doctoral studies under the mentorship of Kay Holekamp at MSU. Her research was bolstered by support from the Dr. Marvin Hensley Endowed Scholarship Fund in Zoology.

“Social relationships can overcome barriers to mobbing and let hyenas achieve cooperation,” Montgomery said, further adding that greetings among hyenas and the strength of their social bonds play pivotal roles in determining their likelihood to engage in mobbing behavior.

Complex social structures 

Spotted hyenas are intriguing social animals characterized by complex social structures similar to those found in baboons and other primates. Researchers study hyenas not only to comprehend cooperative behaviors in wildlife but also to gain insights into such behaviors in humans.

Kenna Lehmann, another lead author who was part of Holekamp’s team during her doctoral studies and is now an assistant professor at MSU, emphasizes the significance of long-term relationships built among hyenas. She notes that their interactions go beyond mere transactional arrangements. “It’s not just, ‘I’ll give you a zebra leg if you help,’” as she puts it.

Unique characteristics 

Holekamp, who has dedicated 35 years to studying hyenas in Kenya, expresses her fascination with these creatures. “I went to Kenya in 1988 thinking I’d do a dissertation-length project – three or four years – with hyenas, then I’d move on to study dolphins or monkeys or some other animals.” However, the unique characteristics of hyenas kept her captivated.

For example, female spotted hyenas possess pseudo-penises, a biological anomaly that challenges conventional understanding. Although this particular aspect doesn’t directly relate to the current study, it highlights the hyenas’ propensity to defy established biological norms. 

“Spotted hyenas appear to violate many of the basic rules of mammalian biology,” Holekamp said, thus making them intriguing subjects for scientific investigation.

Focus of the study 

Both Tracy Montgomery and Kenna Lehmann, under the guidance of Kay Holekamp, became intrigued by the rules governing hyenas’ behavior when mobbing lions. They sought to understand why hyenas engage in this risky behavior and what motivates them. 

Notably, their research revealed that lions were responsible for the deaths of hyenas in over 25 percent of cases where the cause of death could be ascertained.

Tangible benefits of mobbing 

Lions and hyenas often share territories, prompting Lehmann and Montgomery to initially examine mobbing behavior through the lens of its tangible benefits, such as protecting food resources from lions. 

In a previous report in 2017, the team demonstrated that mobbing was not limited to scenarios with immediate benefits but also occurred without any apparent advantages.

New insights 

In their recent study, the researchers delved deeper into mobbing behavior to explore other underlying motivations. During this exploration, they discovered that mobbing was more prevalent when the risk of harm or death to hyenas was lower, even in situations devoid of immediate benefits. 

For instance, hyenas were more likely to engage in mobbing when there were no male lions present, as male lions are larger and more hazardous to hyenas. Conversely, among spotted hyenas, where females are larger than males, females were more inclined to participate in mobbing.

Meticulous observation 

However, the most noteworthy aspect of mobbing behavior was its social dimension, a discovery made possible by the meticulous observation of hyenas spanning several generations within the same habitat over 35 years. 

Throughout this extended period, the research team maintained a continuous presence at their research camp in the Maasai Mara National Reserve, with multiple collaborators contributing to the project.

Long-term commitment 

The significance of the long-term commitment to this research became evident as mobbing events are relatively infrequent. Over the course of three decades, the team witnessed approximately 1,000 interactions involving hyenas and lions, with only a fraction of those interactions providing the comprehensive data required for detailed analysis. 

These interactions are typically fast-paced, involve numerous hyenas and lions, and are characterized by rapid movement, making precise data recording a significant challenge.

Valuable data

Out of the roughly 1,000 interactions observed, only 325 yielded sufficiently robust data for Montgomery and Lehmann to conduct their analyses and make their discoveries. They credit the dedication and efforts of students, research assistants, and other collaborators over the past 30 years for their ability to standardize and organize field observations into usable datasets.

The researchers continue to explore the wealth of insights that these datasets may hold. “Finding these results was really exciting, but I feel like the fun part of science is you answer a question and you immediately have 50 more. There are so many more things that we need to do with this data,” Montgomery concluded.

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