Raiding frequencies by male versus female groups

When elephants raid crops, they may do so solitarily, as in the case of adult or subadult bulls, or in such social groupings as bull groups, family herds, or families with one or more adult bulls attached. By comparing the relative frequency of crop raids by these categories to the elephant population structure, we can understand possible differences between the sexes in raiding behavior. A striking feature that emerges from most studies is the much higher propensity for male elephants to raid crops. I have mentioned that, on average, an adult bull entered cultivation six times (49 nights) more frequently as a female-led family group (8 nights) during my 1981-1982 study in southern India. In a different part of the elephant's range in southern India, Ramesh Kumar computed a similar difference between the sexes in raiding. Comparable figures are not available from elsewhere, but can be approximated from data on relative raiding frequencies. Of 1,672 instances of raids in northwestern Sri Lanka, Mangala de Silva found 75% to be due to solitary bulls, 7.6% by pairs (which undoubtedly would have been mostly bull pairs), and the rest by larger groups. Thus, adult males were responsible for 80%-85% of all raids, while these probably constituted only about 15%-20% of the population. This again implies a several-fold difference between bulls and family groups in raiding propensity.

The few studies in Africa also point to a similar pattern. At Liwonde in Malawi, about 85% of raids recorded by Roy Bhima were by individual bulls or bull groups. As aerial surveys showed a slight excess of female herds compared to bull groups, it is again clear that bulls ventured out of the park into cultivation far more often. Two studies in Zimbabwe came to similar conclusions. Richard Hoare's documentation of crop raiding in the northern Sebungwe region revealed that 79% of raids were perpetrated by solitary bulls or bull groups, and 9% were by mixed groups in which at least one large male was present. Ferrel Osborn observed that virtually all crop raiding at Sengwa was by bull elephants. The Zimbabwean elephants had a natural population structure, and thus the male bias in raiding is very striking in these two studies.

The majority of studies thus clearly establish that, on average, an adult male elephant is more likely to raid crop fields than would a female-led herd, a behavioral difference that should have a biological basis. Nevertheless, the number of raids by family groups may also be significant and perhaps more than that of bulls on an absolute or even a per capita basis in some regions. These warrant a closer examination.

Some observers loosely report that family groups raid more often than do bulls without relating the raiding frequencies to population data. In some cases, the raiding "herds" may have included one or more adult bulls or even have been an all-male group. One region where family groups seem to raid crops as frequently as the bulls do is Central India, which has been investigated by Hemant Datye. Incidentally, Datye's statement that family herds raid more often than the bulls is not backed by data relating this to the population structure. The small population of elephants of Dalma Sanctuary in southern Bihar (now Jharkhand State) has since 1987 been making deep forays eastward into the state of West Bengal. Utilizing small patches of regenerating forest, these elephants cause heavy damage to paddy fields. Another region where family herds have caused considerably more damage to crops than have bulls on a per capita basis is in the southern Indian state of Andhra Pradesh. After elephants had become extinct at least two centuries earlier, several herds of elephants, including some bulls, immigrated into this state from a much larger population further south beginning in 1983.

Comparable documentation from Africa is scant. A possible example is the Waga-Logone region of northern Cameroon, where Martin Tchamba records that the number of crop-raiding elephants in the rainy season increased from about 50 in 1991 to 330 in 1997. This seems related to shifts in seasonal movement patterns of certain elephant herds. It is interesting to note that the elephants in northern Cameroon have mostly been immigrant from neighboring Chad. Since about 1947, the population here has built up to several hundred elephants with successive waves of immigration.

The overall pattern that emerges is that, in the relatively intact and extensive habitats that harbor large elephant numbers, the males exhibit a much greater propensity to raid cultivated fields compared to female-led herds. Raiding by female-led herds increases with greater fragmentation of habitat. The few recorded instances when family groups had equal or even higher propensity than the bulls to raid were those for which habitats were highly fragmented, populations were relatively small, and environmental factors forced the herds to disperse over long distances, perhaps in search of newer habitats. I discuss the possible significance of this pattern in another section.

As opposed to the per capita frequency of raids by bulls and family herds, the relative absolute frequency of raids by the social groups in a region would depend on their differential propensity to raid and their representation in the population. To take an extreme example, if all adult bulls are eliminated from a population, then 100% of raids (whether few or many) would be by family groups. In the larger elephant populations with a normal age and sex structure, over 80% of all crop raids in the region seem to be due to bulls (the examples being Sri Lanka, Zimbabwe, and Malawi). In such populations, almost free from ivory poaching, the adult bulls are likely to constitute about 15% of the population. As the sex ratios become more female biased through selective hunting of males, the relative proportion of raids by bulls decreases. In my study area, the adult bulls constituted 7% of the elephant population during 1981-1982, but were responsible for 70% of nearly 800 nights of raiding in 12 villages. Bulls were responsible for 54% of about 1,450 raiding incidents recorded by Ramesh Kumar during 1989-1991 in Hosur Division. Although he does not give population figures, it can be assumed that the poaching wave in southern India during the 1980s, which also affected the Hosur Division, would have impacted the adult male segment.

The relative extent of raiding by the various social groups can also be expressed in terms of actual damage inflicted. This would depend on the group size difference (thus, raiding by a family herd could result in greater damage by trampling and consumption compared to that by a solitary bull) and the tenacity of raiding (a solitary bull that spends 10 hours raiding could inflict more damage than a family herd that raids for an hour). Damage itself could be expressed as area of the field that is affected, reduction in crop yield, or economic value of the loss. In my study, the bulls were responsible for about 60% of the total loss in yield to millet and cereal crop. In economic terms, this was slightly higher because coconut trees, which have higher economic value, were almost exclusively damaged by bulls. In contrast, about 65% of the damage was attributed to family herds in a sample of 194 raids in the Nilgiris in southern India, recorded by M. Balasubramanian and colleagues during 1992. Although they do not present population data for this range, it is clear that the reduction in adult males to less than 3% of the population (based on my records) was responsible for this pattern. Interestingly, they concede that, on a per capita basis, the adult bulls raided more often than did the family herds. In absolute terms, the amount of crop damage caused by elephants was reduced significantly in many parts of southern India because of the poaching of tusked males. As this trend continues, the family groups would cause a progressively higher proportion of the reduced damage.

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