The evolution of elephant society

The raison d'etre of elephant society has been explained in evolutionary terms as the maximization of the genetic fitness of its members. Cooperation among the larger cows of a family in group defense of young elephants, which are vulnerable to predators such as the tiger in Asia or the lion in Africa, would constitute one such benefit. If group defense is indeed one of the primary functions of elephant families, we could expect larger family groups in regions where predatory threats are greater. The data on family group sizes broadly support this expectation. Larger families are seen in African savannas and in Asian dry forests, where the larger predators are common. In contrast, the small, single-matriarch families are seen in Central African rain forests, which do not have any large predator such as the lion and only low densities of medium-size predators such as leopards.

Group size is also strongly influenced by the availability and dispersion of food resources; the greater the food availability is (as in savannas and dry forests), the larger is the group size. The resources factor in fact could completely obscure any considerations of predatory threat. However, it is interesting to note that elephant family groups are much smaller in Central African rain forests compared to those in Malaysian rain forests, with presumably similar resource availability. The Malaysian forests are home to the tiger, while no predators of comparable size are to be found in African rain forests.

The apparent altruistic behavior of female elephants can be justified by the high degree of relatedness among members of the family; in genetic terms, such behavior enhances the "inclusive fitness" of the donor through "kin selection." After all, by saving a niece or a nephew with whom she shares a significant proportion of her genes, a matriarch also ensures that copies of her genes are passed on to future generations. There is obviously a cost attached to allo-mothering, especially if this means delayed reproduction through suckling a sibling's calf. Phyllis Lee's observations, however, show that allosuckling is quite rare. In a long-lived species in which individuals recognize not only their immediate kin, but also less-related members within a social group, there is also a high chance of reciprocity in such altruistic behavior. Allomothering thus has to be seen as not only promoting inclusive fitness, but also benefiting from reciprocity.

A stable family also provides the ideal milieu for younger elephants to learn much of their behaviors from the elders. While some of these behaviors, such as knowledge of what plants constitute food, may contribute to longer-term fitness, others (such as the appropriate response to a predatory attack) could be crucial to immediate survival. A calf 's brain weighs only 35% of its ultimate weight of about 6 kg during adulthood. This provides considerable scope for learning: What better than an extended stable family setting for a rich learning experience?

We are barely beginning to understand objectively the importance of the leadership role of the matriarch in survival of her family, an aspect that many elephant observers have speculated upon. In a highly social, intelligent, and long-lived animal, the matriarch is virtually an encyclopedia of stored knowledge that her family can draw on. By leading her family or higher social entity to the best foraging and watering grounds on a daily or seasonal basis or rediscovering a water source used in the distant past during a time of drought, the matriarch enhances the fitness of her social group.

While cooperation among adult female elephants has been much emphasized, little attention has been paid to competition among the matriarchs. Competition and conflict, after all, are as much a feature of animal societies as is cooperation, and perhaps they are even more integral to their functioning. Based on her observations in Kenya's Tsavo West National Park during the 1970s, Holly Dublin has drawn attention to several possible arenas of competition among female elephants. All these relate directly or indirectly to the relative reproductive success of female elephants. Antagonistic interactions between female elephants of unrelated social groups have been described by some observers, but their outcome in terms of benefits or costs to the players has never been quantified. A matriarch who successfully defends resources such as food and water, especially at relevant times during the year, could ensure lower mortality and better reproduction within her social group.

Dublin's observations at Tsavo indicated that calves born before the major annual peak in rainfall had a lower mortality than those born after this rainfall peak. Further, she observed that most calves born before the rainfall peak were born to socially dominant mothers, as determined from dyadic interactions, while calves born after the peak were mostly born to subdominant cows. Given the gestation period of about 20-22 months, the inference here is that female elephants that are able to time their ovulation and breeding to coincide with the peak rains, through better access to high-quality forage and mates, would emerge as winners. At the same time, the dominant females would have to suppress the reproductive efforts of other females. At Tsavo, the dominant females seemed to be achieving this goal through increased aggression toward subdominant females. In several mammals, it is well known that intrasexual competition could result in suppression of or delayed ovulation, failed implantation, or even abortion among the subordinate animals. The physiological mechanisms of such action are poorly understood. Dominant females could also monopolize access, through overt and subtle behaviors, to the dominant musth bulls for mating during the most favorable season. How elephant societies achieve the right balance between cooperation and competition is clearly a subject wide open to investigation.

The subject of intelligence in elephants itself has been hardly investigated since the pioneering efforts of Bernard Rensch reported in 1957. The ability of an elephant to understand and respond to a substantial vocabulary of commands from its trainer is legendary. Rensch carried out a series of experiments to actually measure the learning capacity of a 5-year-old female Asian elephant at the M√ľnster Zoo in Germany. The elephant was trained to discriminate among various visual patterns through a system of rewards for the correct response. A surprising result was that the elephant could simultaneously keep in memory the meaning of 20 visual stimulus pairs, having mastered these superbly. The scores in these tests suggested that the elephant could have mastered a bigger vocabulary given more time and training, but the observers felt this would not add any significant information about the animal's learning abilities.

Tool use by an animal is generally considered characteristic of higher intelligence. It is well known that Asian elephants use twigs to scratch their skin and branches as tools to repel flies from parts of the body they cannot reach with their trunks (fig. 4.25). This behavior has also been observed in African elephants, although less frequently. Benjamin and Lynette Hart studied such tool use and its context in captive Asian elephants used for tourist rides in Nepal. They concluded that elephants indeed use branches as switches to dislodge parasitic flies, and this was not merely stereotypic behavior related to confinement. Further, they estimated that fly switching reduced fly count by 43%, a level significant in reducing loss of blood. Elephants also fashioned the branches intelligently to increase their efficiency as tools. The ability of elephants to create images with a paintbrush and colors is also being viewed as a demonstration not only of its manipulative skills, but also its superior discriminatory powers.

Intelligence in the social sphere, especially among the matriarchs, could be an important determinant of biological fitness of their social groups. Perhaps the most exciting new research on this subject is that of Karen McComb, who worked with Cynthia Moss and other associates at Amboseli. Their playback experiments of infrasonic calls revealed an unusually high ability among

Figure 4.25

A captive Asian elephant uses a branch for switching flies off its skin. Such tool use is indicative of higher intelligence in mammals. (Photo courtesy of Ben Hart.)

Figure 4.25

A captive Asian elephant uses a branch for switching flies off its skin. Such tool use is indicative of higher intelligence in mammals. (Photo courtesy of Ben Hart.)

Association index
Asian Elephant Population Graph

Figure 4.26

The discriminatory ability of Amboseli's elephant matriarchs to infrasound playback calls of other females. The association index is a measure of previous association observed between the matriarch and the caller. Two age categories of matriarchs are depicted: younger matriarchs (<35 years, dashed line) and older matriarchs (>55 years, solid line). The graphs describe probabilities of (a) bunching and (b) smelling. (From McComb et al. 2001, Science, 292, 491494, Figure 1. Reprinted with the permission of the American Association for the Advancement of Science.)

Association index

Figure 4.26

The discriminatory ability of Amboseli's elephant matriarchs to infrasound playback calls of other females. The association index is a measure of previous association observed between the matriarch and the caller. Two age categories of matriarchs are depicted: younger matriarchs (<35 years, dashed line) and older matriarchs (>55 years, solid line). The graphs describe probabilities of (a) bunching and (b) smelling. (From McComb et al. 2001, Science, 292, 491494, Figure 1. Reprinted with the permission of the American Association for the Advancement of Science.)

female elephants to discriminate between calls of individuals associated with them to varying degrees (see section 4.3.2). The typical response to a playback from a closely associated female was to call in return, while with a less-familiar female, it was negative behavior, such as bunching together or smelling with raised trunk. Families, however, differed in their abilities to discriminate between calls and respond appropriately; the age of the matriarch was a key determinant of this ability. The tendency to bunch in negative fashion declined with increased association with the calling family (the association was represented as an index calculated on the basis of field observations of these families). With older matriarchs (>55 years), there was virtually no bunching when calls of high-association families were played back (fig. 4.26). The discriminatory abilities of younger matriarchs (<35 years) were much poorer. Not only did their families show a much higher probability of bunching in response to playback calls, but they also continued to bunch at relatively high frequencies even in response to calls from high-association families. With respect to the behavior of smelling, the younger matriarchs could not discriminate between calls of low- and high-association families. Several other variables, such as number of females in the family group, the age of females other than the matriarch, the number and age of calves, and the presence of adult bulls that could confound the results of such experiments were not statistically significant. McComb and associates thus concluded that families with older matriarchs have either "larger networks of vocal recognition or greater social confidence" than do families with younger matriarchs.

The most interesting part of this work was the translation of these observations to biological fitness of the family groups. From the demographic records of identified elephants of Amboseli, it was seen that "the age of the matriarch was a significant predictor of the number of calves produced by the family per female reproductive year" (McComb et al. 2001, p. 493). In other words, families with older matriarchs possessing superior discriminatory abilities were also more successful in reproducing. Populations such as that at Amboseli, where long-term records of identified individuals are being kept, provide the best opportunity for understanding the evolution of social life in this long-lived animal.

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