Elephant contraception

Elephant populations are known to double every ten years, and this obviously represents a considerable risk for biodiversity conservation as a result of the cumulative impact on vegetation composition and structure over time. However, recent trials on a private reserve in the Lowveld have shown immunocontraception to be an extremely effective method to stabilise elephant populations in relatively small conservation areas and this obviously represents an exciting new possibility for elephant management.

The contraceptive vaccine (porcine zona pellucida, or pZP) works by blocking the sperm receptor sites on the ovulated eggs, thus forming a physical barrier between the sperm and egg. Hence, the vaccine is not only highly effective but is also safe and reversible when annual re-vaccinations are stopped. The application does not require the cows to be immobilised as the vaccination is simply applied using drop-out darts delivered from a helicopter. The vaccination protocol entails a primary vaccination followed by two boosters at 3-4 week intervals during the first year and a single annual booster thereafter. Taking existing pregnancies into account (which are not affected by the vaccine), stabilisation of the population occurs after three years.

pZP contraception has been successfully applied at Makalali Game Reserve since 2000 with 100% reproductive control. More recently, other private reserves have adopted this procedure as a means to manage their elephant populations. To date, no changes in social behaviour have been recorded. However, the use of pZP contraception as a mechanism to manage elephant populations in small reserves remains a relatively recent development and there is therefore limited data on the response of the elephant population in terms of social behaviour. Consequently, Welgevonden is in a position to play an important role in advancing research on contraception as a means to control elephant numbers in small, confined reserves.

Given the ecological requirements for flux within an ecosystem, an elephant population should not be allowed to remain at a constant level over an extended period of time. The challenge is to identify upper and lower limits of acceptable change and manage the population within these limits. The need to reduce numbers from time to time infers that relocation and/or culling of elephants in confined reserves will continue to be necessary, but contraception will enable management to better control the frequency and extent of such interventions.

The primary vaccination was completed at the end of September, with 42 elephant cows and young females being vaccinated. Although the herds initially reacted to the low-flying helicopter, no problems were reported and the herds soon reverted to their normal, calm demeanour.