Management of overabundant populations

The most contentious issue relating to the conservation of African elephants during the 1960s and 1970s was the management of locally overabundant populations. A heated debate raged over the issue of whether such populations should be managed through culling of elephants (fig. 9.5). The spate of ivory poaching that swept through Africa during the 1970s and 1980s put an end to this controversy in many countries. However, it is likely that, with the decline of poaching and better protection in many parts of the species' range, the increasing elephant populations could once again rekindle the debate over culling. While there have been no serious demands for reducing Asian elephant populations on grounds of overabundance, we must keep in mind that elephant densities in parts of southern India are among the highest seen anywhere, while those in southeastern Sri Lanka also are relatively high. Although the killing of elephants in these countries can be ruled out, there could be demands for their capture.

Figure 9.5

A team inspects a group of elephants culled in Zimbabwe's Sengwa Wildlife Research Area. (Photo courtesy of Richard Hoare.)

Figure 9.5

A team inspects a group of elephants culled in Zimbabwe's Sengwa Wildlife Research Area. (Photo courtesy of Richard Hoare.)

The arguments for culling African elephants have been articulated at length by observers such as U. de V. Pienaar, Irven Buss, and Richard Laws. Many parts of the savanna elephant's range in eastern and southern Africa had become overstocked with elephants. This was the result of loss of habitat, thereby compressing elephants into smaller areas at higher densities, and of harassment of elephants by poachers and people that caused elephants to seek the relative safety of protected areas.

In former times, low levels of subsistence hunting would have held elephant populations under check, but the setting up of protected areas has altered their demography. At such artificially high densities, the elephants were damaging and killing many tree species at rates that exceeded their regenerating capacities, thereby converting woodlands into grasslands. This vegetation change represented an esthetic loss for the landscape apart from having ecological implications for the elephant populations themselves and for the local biodiversity. The changing nature of the vegetation, from woodland to grassland, would be detrimental to elephants through loss of shade and a shift to a less-nutritious diet of grass.

Work by D.M.H. Cumming and associates showed significant declines in the diversity of birds, ants, and certain other taxa in places where elephants had caused a decline in tree canopy. The landscape changes occurring in many parts of the elephant's range were possibly unprecedented and were a threat to the continued existence of these ecosystems.

The most rational way of managing these ecosystems would be to cull elephant populations (and other large herbivores as necessary) to densities below the carrying capacity of the habitat. This would not only benefit the broader community of plants and animals, but also generate revenues for the local rural economy and for park management. It was foolish to argue that we should let nature take its own course because people had created this situation in the first place, and thus intervention was appropriate. Such management through culling of elephants would help maintain a high rate of animal productivity, utilize rather than waste this production, and ensure the persistence of other biological elements in the landscape.

The counterarguments to culling elephants have been equally strong. The evidence for compression of elephant populations was weak in many regions facing a specter of declining woodlands. Factors other than elephants, such as fire or natural climatic factors, were clearly implicated in tree decline in some places. Natural ecosystem processes, including the long-term dynamics of climate, trees, elephants, and other herbivores, were poorly understood. There was historical evidence, for instance, that the Tsavo ecosystem was in a relatively open state with low elephant numbers at the turn of the twentieth century. Clive Spinage argued that elephant populations were now resurgent after being depressed by exploitation for ivory during the late nineteenth century. In short, there was no need for humans to interfere with the natural course of events through any culling of elephants. Comparisons with wildlife management through culling in North America did not prove anything. Anthony Sin clair aptly summed up this view when he stated that culling was based on "the ridiculous conclusion that the only good herbivore population is one vanish-ingly small" (1981, p. 255)

Ethical arguments further reinforced the anticulling sentiments. Killing a highly intelligent, sensitive, and social animal, and in such large numbers, was morally repugnant. Elephants that were targeted during culls seemed to transmit the trauma of the event to other elephants in the area before being killed. This was initially a very puzzling observation, but the discovery of infrasound communication solved this mystery. The indiscriminate targeting of elephant family groups also meant that several matriarchs, repositories of traditional knowledge crucial for survival, would be killed, resulting in severe disruption of the fabric of elephant society.

Organized culling of elephants in eastern and southern Africa began during the mid-1960s. One of the earliest culls took place in 1966 at Tsavo National Park in Kenya, but was abandoned after about 300 elephants were killed. This made little impact on Tsavo's huge elephant population. Kenya decided to follow a hands-off policy in managing abundant elephant populations, a policy that came under severe criticism after an estimated 6,000 of Tsavo's 20,000 or more elephants died during the drought of 1970-1971. Many more elephants died in the larger ecological unit, and the effects of the drought continued to result in mortality that was higher than average until 1975. Two culls of similar size were organized in Tanzania's Mkomazi Game Reserve (east and central) in 1968 and 1969, but were again discontinued. Uganda was one eastern African country that went ahead with a major cull in the Murchison (Kabalega) Falls National Park (where about 2,000 elephants were taken) and in the vicinity of the Budongo Forest (where 300 elephants were taken) during 1965-1967. It was another matter that political events in Uganda leading to a civil war resulted in overthrowing any rational management plan for elephants, whose population crashed by 90% from indiscriminate killing. Elsewhere in eastern Africa, poaching for ivory also made it redundant to cull elephants.

Southern African countries, with the exception of Zambia, have a longer history of culling as part of their management of elephant populations. Zambia organized a major cull during 1965-1969 in the Luangwa Valley, where about 1,500 elephants were taken. Culling in Zimbabwe has been widespread across the elephant range, including areas where there has been no perceptible damage to vegetation. Records compiled by Rowan Martin show a minimum of 46,775 elephants killed during 1960-1991, with the most (20,000+) being taken from the Matabeleland North, including the Hwange National Park. About 570 elephants were culled in Namibia's Etosha National Park during 1983-1985. South Africa has a persistent history of culling elephants, primarily in Kruger National Park, where most of the country's elephants are found. The objective of culling has been to keep the elephant population at about 7,000 individuals (density to 0.32 elephants/km ) with accepted fluctuations between 6,000 and 8,500 individuals in the 20,000-km park. To meet these objectives, an organized culling program has been in operation since 1967;

this program removed about 17,200 elephants during 1967-1996, an annual average of 6.7% of Kruger National Park's elephant population estimated through aerial counts. These figures suggest that about 65,000 elephants have been killed in Africa, mostly in Zimbabwe and South Africa, over a period of three decades as part of controlling populations perceived to be overabundant.

The methods of killing elephants and the end use of the carcasses have varied with region and time. The Ugandan culls were carried out by locating elephant groups from an aircraft and then sending in professional teams, which shot entire families on foot within a couple of minutes to prevent any survivors with traumatic memories of the event. The carcasses were used for a variety of scientific investigations on the biology of elephants. The southern African culls have combined research with an end use for most of the elephant products. In Zambia, the elephants were darted with succinylcholine, a drug that kills by paralyzing the respiratory muscles. Carcasses were transported to an abattoir for hygienic processing of the meat for sale. The drug used breaks down on heating, and thus the meat is safe for human consumption. At Kruger also, elephants have been darted, from a helicopter, with massive doses of succinyl-choline, while ground teams quickly move in to shoot the darted animals. The carcasses are processed in an abattoir, with the meat being shared with the park staff or sold to shops in the vicinity and the skin converted into leather goods. In recent decades, Zimbabwe has linked its elephant culling to the much-publicized CAMPFIRE program under which revenues from hunting are shared with local village councils as incentive for protecting wildlife.

What has been learned so far about managing abundant elephant populations? The African observers agree that the more extreme predictions of irreversible population disaster and desertification associated with abundant elephant populations were without basis. Models of elephant-vegetation dynamics have also pointed to the ineffectiveness of culling elephants as a means of preventing the decline of tree populations (chapter 6). By the time a problem is recognized, any cull has to be of unacceptable magnitude for possible stabilization of the situation. Control of fire or even the giraffe could achieve the objective in some situations, such as for Acacia woodlands in eastern Africa. Elephant culls have been based on rather arbitrarily defined carrying capacities. The concept of carrying capacity, while of great theoretical interest in ecology, is rather difficult to apply in field management. This is especially true as even the theory has moved away from equilibrium in ecological systems to a better appreciation of the dynamic nature of ecosystems. Steven McLeod is thus in favor of discarding the concept of carrying capacity in describing plant-herbivore interactions in highly variable environments.

We are also slowly realizing that the problem of overabundant elephant populations can be traced to human intervention, not only through compression, but also through habitat management practices, such as creating artificial waterholes. Based on my observations in southern India, I had pointed out that such provisioning of elephant populations with water could result in artifi cially high animal densities, much above the carrying capacity set by the vegetation. The high densities would occur through a lowering of dry season mortality rates in elephants, resulting in strongly positive population growth rates (section 9.5). A similar mechanism for the growing elephant population in Kruger National Park, South Africa, has been suggested. Added to this is the intriguing suggestion by Antoni Milewski that reproductive rates of elephants may have been boosted by the high iodine content in artificial bore water supplied to animals in conservation areas of southern Africa. A wildlife management practice that is seemingly beneficial may have inadvertently set the stage for a major management dilemma over the longer term.

There have been few objective analyses of the consequences of culling on elephant populations and their habitats. Ian Whyte, Rudi van Aarde, and Stuart Pimm have made a 1998 assessment of culling in Kruger National Park. There were few elephants in the Kruger region during the early decades of the twentieth century. Five years after the park was proclaimed in 1926, there were believed to be only 135 elephants there. The elephant population increased to an estimated 6,600 in 1967, when culling began, and to 8,800 in 1970. Some of the increase was possibly due to immigration from neighboring Mozambique, but after 1972, this factor was negligible. Although the culls prior to 1984 took place all over the park without a clear plan, the park was then divided into four management units for subsequent culls. The annual quota for the park was taken from only one of these subpopulations during a given year. A demographic analysis of Kruger's elephant population showed significant responses to culls. When year-to-year changes in elephant densities were examined, these were clearly density dependent, as could have been anticipated from theory. This implied that culls immediately following an estimated high elephant density would be premature; the density would have leveled off or even declined without further intervention. The census data also showed that, when elephant densities exceeded 0.37 individuals/km , they generally declined without culling. Thus, many of the culls were unnecessary. Another interesting observation was that, immediately following a cull, the elephant numbers declined locally because of disturbance and emigration, but soon thereafter, they increased again as the elephants moved back into the subpopulation. One suggestion from this analysis was that a subpopulation should be culled only when elephant density exceeded 0.37 individuals/km2 for more than a year.

The ethical dilemma over culling has also prompted new thinking into means of controlling surging elephant populations. If extra iodine in artificial waterholes is stimulating reproduction in elephants, it may be possible to regulate the supply of iodine through selection of watering points.

Birth control aimed at females is one possible means of regulating an elephant population. The technical development of birth control measures requires a better understanding of the elephant's rather complex reproductive cycle (chapter 3) as well as suitable delivery systems. The options include termination of pregnancy, contraception, and sterilization. Each method has its advantages and drawbacks. The likely effect of any particular method on the health of the individual animal and the possible behavioral consequences must be carefully evaluated.

Inducing a pregnant elephant to abort its fetus may have adverse health effects as well as behavioral changes. Contraception is a more acceptable solution, especially if a method with few side effects can be developed. Steroid hormones have the disadvantage of possible health effects and problems in packing sufficient quantity in an implant of a size that can be delivered remotely into elephants. Some experiments at Kruger with implanting capsules of estradiol-17 resulted in continued high concentration of this hormone, prolonged sexual receptivity, harassment by bulls, and separation or expulsion of these female elephants from their breeding groups.

An immunocontraceptive vaccine causes an animal's immune system to produce antibodies that prevent fertilization, with possibly fewer side effects than steroid hormones. R. A. Fayrer-Hosken and a support team have recently carried out trials at Kruger on 41 adult female elephants identified as nonpreg-nant with a vaccine developed from the pig's zona pellucida (PZP). Of these elephants, 21 were initially vaccinated, while the other 20 controls received a placebo. All elephants were fitted with radiotransmitters for subsequent monitoring. The vaccinated elephants received booster doses after 6 weeks and 6 months. A year later, 19 of the treated elephants were recaptured and scanned by ultrasound for pregnancy; of these, 9 (47%) were pregnant. By contrast, 16 (89%) of the 18 control elephants that were recaptured were pregnant. In a new set of experiments, 10 elephants received the initial vaccination followed by boosters 2 or 4 weeks later. Only 2 (20%) of these 10 elephants were pregnant after 10 months. This immunocontraceptive vaccine was also shown to be reversible, with no deleterious effects on reproductive cycling, as seen from subsequent pregnancy of some of the vaccinated animals.

If the management objectives are to curb elephant population growth, it is insufficient to develop an acceptable contraception method without understanding the actual logistics of the field operations in relation to elephant demography. The demographic characteristics of elephant populations vary from one region to another and with time. It is important to understand a priori which changes in female fertility will be needed to curb or reverse population growth. An elephant population with an adult female mortality rate less than 3% per annum, an age at first calving of 12-15 years, and an intercalving interval of 4-7 years is most likely a growing population. A slow-growing, long-lived species such as the elephant is more sensitive demographically to changes in mortality rates than in fertility rates. By delaying the age at first calving by a few years and by widening the intercalving interval to the desired level, a growing population will not be curbed for at least a decade. It must also be kept in mind that the age pyramid of a population with reducing fertility will shift toward older individuals, thus maintaining equal or higher biomass with corresponding per capita forage requirements.

All this means that an elephant population under some form of fertility regulation will continue to make an impact on its habitat in the short-term. For Kruger, Ian Whyte and associates have estimated that about 75% of 3,000 reproductively active cow elephants would have to be administered contraceptives to ensure zero population growth. The time lag effects in demography also mean that, with a population growing in the short term, a total of about 4,000 female elephants, and not just 2,250 elephants, may have to receive contraceptives by the time the objective of zero growth is actually achieved. An alternative would be to selectively cull 250 of 300 cows at Kruger that are just about to enter the reproductive age class. This would stabilize the population. The word cull could be substituted by sterilize to achieve the same end. This would need the development of an irreversible contraceptive. The ethics of such an action should be openly discussed before initiating management action. Fertility regulation in elephants, in any case, should be thought of as a management option with a medium-to-long-term perspective.

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