Managing the elephants of Kruger National Park

Abstract

The elephant population in Kruger National Park, Republic of South Africa, is growing rapidly. To prevent damage to the Park's ecosystems, the management has culled about 7% of the population annually. Such culls are very controversial. At first glance, contraceptives seem an attractive alternative means of control. We examine contraception as a management option, review the relevant aspects of elephant reproduction, physiology and demography and conclude that this optimism is probably misplaced. First, contraceptives have a wide range of physiological and behavioural side-effects that may prove to be damaging to the individual female and those around her. Second, the elephants in the Park have near-maximal growth rates with inter-calving intervals of less than four years. To achieve zero population growth, about three-quarters of the adult female elephants would need to be on contraceptives. There are no simple alternatives. The smallest numerical target for controlling population numbers is to kill or sterilize females about to become pregnant for the first time. Such a solution is unlikely to appease those who consider killing elephants to be unethical. It may, however, be the one closest to the natural patterns of elephant mortality.

Fluctuations in abundance of large herbivore populations: insights into the influence of dry season rainfall and elephant numbers from long‐term data

“…In such areas, the potential impacts of elephants on other forms of biodiversity have been of great concern to managers and accordingly, the need to control their populations has been suggested and widely debated (e.g. Butler, 1998; Whyte, van Aarde & Pimm, 1998; van Aarde & Jackson, 2007). Elephants are megaherbivores (herbivores weighting over 1000 kg) that need to harvest and process a large amount of vegetation (Owen‐Smith, 1988), and consequently may impact on ecological niches of other animals through the modification of habitats and changes in the abundance and structure of the food resources.…”

Modelling the effectiveness of contraception for controlling introduced populations of elephant in South Africa

“…Birth sex ratio was 1 : 1 (Laws, Parker & Johnstone, 1975; Calef, 1988; Mackey et al. , 2006 ), age at menopause was 50 years (Hanks & Mcintosh, 1973; Owen‐Smith, 1988) and maximum age was set to 60 years (Hanks & Mcintosh, 1973; Wu & Botkin, 1980; Whyte et al. , 1998).…”

“…, 1998). In the baseline simulations, probability of survival was set to 1 for all ages below the maximum age, following Whyte et al. (1998) and because little or no mortality has been observed in the three populations examined (Slotow et al.…”

“…As the application of this technology to elephant management is new, little is known about the potential longer‐term effects of immunocontraception on population growth. Dobson (1993) and Whyte, Van Aarde & Pimm (1998) employed age‐structured models to examine potential long‐term effectiveness of contraception in large established elephant populations – Amboseli and Kruger National Park (KNP), respectively – with relatively low rates of population growth (average annual rates ≤5%). However, models have not yet been used to make projections of the effectiveness of contraception on small elephant populations that are characterized by high growth rates and young age structures.…”

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

“…The overabundance of wildlife is an ongoing problem, with many pest species increasing to numbers that become detrimental to both the environment and other wildlife species (e.g., elephants (Loxodonta africana), Whyte et al 1998; white tailed deer (Odocoileus virginianus), Warren 1997; feral horses (Equus caballus), Wagner 1983; Canadian geese (Branta canadensis), Conover and Chasko 1985). Traditionally, populations of 3 overabundant wildlife were controlled by lethal control or permanent removals.…”