The socioecology of elephants

More the merrier' is an adage that suits a fun-filled evening with friends when a lot of food is up for grabs. But when there is just a single slice of tasty pizza, one would prefer to not share it at all! For us humans, our 'group size' tends to change depending on the situation.

But would it surprise you, if you were told that it is also true for elephants? Elephant groups (herds) are generally led, by and consist largely of, females. They have a fission-fusion society like humans do; members regularly join and leave a group. A group is a set of individuals seen associating together, and groups seen in the wild are usually part of a more inclusive social unit called a clan. The females of one clan do not interact with those of another.

One of the reasons for this kind of group dynamics is the number of resources available, like food and water. Larger groups afford better protection against predators but can be maintained only when food is available in plenty. When resources are scarce or dispersed, members of a group tend to compete for food, and being in smaller groups in such situations is advantageous. This type of society is also characteristic of other species such as spider monkeys, chimpanzees, brown hyenas and spotted hyenas.

Group dynamics

While studies have shown that group dynamics and group sizes are affected by the availability of resources, there is no clear understanding of how seasons affect the same. In a study, S Nandini, P Keerthipriya, and TNC Vidya from the Evolutionary and Organismal Biology Unit at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, wanted to see if two different seasons - wet and dry - had any effect on the group size and social structure of female Asian elephants (Elephas maximus). Their findings were published in the journal Animal Behaviour.

For the study, the researchers observed a population of Asian elephants at the Nagarahole and Bandipur National Parks, over a period of five years - from March 2009 to July 2014. The vegetation in the two parks consist largely of dry and moist deciduous forests, and are separated from each other by the Kabini reservoir on the Kabini River. Since it is one of the prime waterbodies in the region, elephants gather here for water and food like grass, bamboo and certain species of trees, shrubs and herbs.  

The researchers carefully identified individual female elephants using their ear, tail and body characteristics. They then identified if they belonged to a particular group by considering certain behaviours - if they moved as a whole towards or away from a water source or salt lick; or if they bunched together and faced the same direction when they were threatened; or if they touched each other's face, mouth or ear and showed support towards other individuals when disturbed. In addition, individuals of the same group tend to stay within 50 to 100 metres of each other. The researchers collected data on the group size and associations of these females with each other during dry and wet seasons.  

The researchers found that at the population level, which includes all identified females aged 10 years and above, group sizes were larger in the dry season and more associations were observed with uncommon females. On the other hand, if common females were considered, they exhibited stronger associations in the wet season.

This, however, was not the case at the clan level. At the clan level, there was no consistent difference in group size or associations. "Elephants were more dispersed in the forest in the wet season and congregated near the Kabini backwaters in the dry season. Thus, seasonality seemed to affect the way in which elephants use their habitats, but not their group size or social structure within clans," explains Nandini.

Various factors

The study also found that irrespective of the number of females in clans, groups within clans retained a similar average size. This suggests that there is some restriction, probably resource availability, that limits group sizes to small numbers. The fission-fusion dynamics of this population, therefore, appeared to be more for clan members to meet up and socialise with multiple clan-mates, while maintaining a small group size, rather than to increase or decrease the size of the groups.

One of the reasons for these extended associations could be allomothering - the non-maternal infant care where a female takes care of the calf of another, to give her some respite from the constant demands of her little one. Other reasons could be to exchange information about the distribution of food and presence of predators, or for strengthening social bonds.

Though the exact importance of these factors in maintaining the observed social structure is not known, the researchers plan to examine them in future. Elephants are highly social creatures which live in a variety of environments. This makes them a good species on which to study socio-ecological models - theories that attempt to explain how behaviour is determined or affected by personal and environmental factors. Yet, despite their potential for such research, most of the work done on elephants in India revolves around human-elephant conflicts or population size estimation or ecology alone.  

"That is why I set up the Kabini Elephant Project in 2009," explains Dr Vidya, talking about the motivation behind this study. The project involves studies that examine the relative roles of ecological factors and individual relationships on behaviour and social organisation. "This has allowed us to monitor hundreds of individually identified elephants in order to study their socioecology. We are continuing our work on understanding the social organisation and looking at how resource availability shapes the social structure and dominance interactions," she says.  

(The author is with Gubbi Labs, a Bengaluru-based research collective)