Asian elephant herds lack clear matriarchs, strict hierarchies: new study

Submitted by Archiver on Tue, 23/10/2018 - 06:20
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Asian elephants do not seem to have clear matriarch-led families. Photo by Bernard Gagnon, licensed under CC BY-SA 3.0.
  • The differences between Asian and African elephants may be the result of their ecological environments, the team posits.
  • The researchers think that stable ecological conditions in Sri Lanka make it easier for Asian elephants to make their own movement decisions without having to rely on very experienced individuals to know where to go or how to avoid predators.
  • But as habitats continue to shrink and elephants are forced into smaller areas where they cannot avoid each other, their weak dominance hierarchies may result in greater conflict between individuals, the researchers think.

Elephants are believed to follow a strict code of conduct.

Younger female elephants are commonly thought to follow the lead of older individuals, relying on their experience and wisdom to find food, water and other resources. The matriarch — the oldest and the most dominant individual — is typically the leader of the herd. But a new study published in Behavioral Ecology challenges this view.

Unlike African elephants that are characterized by strong matriarch-led, unified families, Asian elephant families appear to be less cohesive and seem to lack clear matriarch-leadership, the study found.

“For practical reasons it is good to identify a matriarch because it makes identifying the rest of the group easier,” lead author Shermin de Silva, director of the Uda Walawe Elephant Research Project in Sri Lanka and a researcher at the Colorado State University, told Mongabay. “But in Uda Walawe, not only could I not figure out who the matriarch was because they weren’t always with the same individuals, but it didn’t seem like they exerted any leadership behavior at all. Everyone sort of did what they wanted to do.”

Between 2007 and 2012, de Silva spent time in Sri Lanka’s Uda Walawe National Park, observing behavior of Asian elephant herds. Her team measured signs of dominance among the elephants — such as when an individual aggressively (or gently) pushes another away, or when one individual acts fearful of another individual — and compared their behaviors with those of African elephants at Kenya’s Samburu and Buffalo Springs National Reserves.

The researchers found that Asian elephants showed such little dominance behavior that it was almost impossible to construct linear hierarchies among individuals. African savanna elephants, in contrast, displayed well-defined dominance patterns, with a clear matriarch.

In both Asian and African elephant populations, older elephants did tend to dominate or “win” confrontations more often than individuals of other age groups. But younger Asian elephant females in their reproductive prime were also often the more dominant females within their groups, the researchers observed.

These differences between Asian and African elephants may be the result of their ecological environments, the team posits.

African savanna elephants, for example, have historically lived in environments that have large non-human predators like lions and where resources like food and water are unpredictable. Since these elephants compete for scarce resources and need to avoid predators, dominance hierarchies can be a useful way of resolving conflict without having to get into a confrontation.

The Sri Lankan elephants, on the other hand, live in more productive and predictable environments where they tend to find food and water more easily. They have also evolved on an island free of large non-human predators. The researchers think that these stable ecological conditions in Sri Lanka make it easier for individuals to make their own movement decisions without having to rely on very experienced individuals to know where to go or how to avoid predators. Consequently, the Asian elephants do not have to tolerate being dominated.

Karpagam Chelliah, an Asian elephant expert with the Indian Institute of Science in Bangalore, India, who was not involved in the study, agrees with the reasoning.

“The hypothesis that dominance hierarchies could be weak under stable ecological conditions is a good premise to expect a difference between the African and Asian elephants,” Chelliah told Mongabay. “The findings were not surprising, though. I hardly saw overt interactions between female elephants in the Asian elephant population of Kaziranga National Park in India where food and water availability is even more stable than in Uda Walawe.”

There is, however, a flipside to weak dominance hierarchies as seen in Asian elephants, de Silva said, especially as their habitats continue to shrink and the animals are forced into smaller areas where they cannot avoid conflict.

“Animals need to be able to get away from each other, find resources without having to compete with each other,” she said. “If they are increasingly constrained by habitat loss or management strategies, then that might impede their ability to resolve conflict more peacefully. Besides the direct competition for resources that the elephants experience, they might also be stressed socially because they are forced into situations where they cannot avoid each other.”

Elephants are also increasingly the focus of intensive management strategies, such as translocations or drives, that remove them from places where they are believed to be in conflict with people. But these practices can alter their social groups and increase stress, de Silva said.

“One of the things that people assume is that if you move the matriarch, you will get the entire group, because socially, they’re supposed to be together,” she said. “But that’s not the case. Our work has shown that elephants aren’t all together all the time. So when you move them, you might be inadvertently separating families or social groups because they weren’t all together then. That disrupts their social relationships and might even have consequences for their survival and reproduction that we don’t really know about.”

Making sense of elephant behavior is hard and conventional observational studies of Asian elephant behavior have their limitations, Chelliah added.

“Elephants could be interacting with each other through communication modes that are beyond the visual and auditory perception of humans,” she said. “So it is possible that two elephants that seemingly did not interact may have actually interacted (using chemical signals, subtle body posture or infra sound) and established their relative dominance. So we may have insufficient information to even conduct a study on dominance network hierarchies with the current methods of observation of elephant behavior.”

 

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