Please note that you are viewing the old Science in Africa website. Please see for our new site!

Science in AfricaLogo Merck: Distributors of fine chemicals and apparatus. Enter here for more information.
September 2004



Overpopulation of elephants:
A mighty dilemma

Melissa Wray

The good news is that elephant populations are thriving in areas of southern Africa after years of hugely successful conservation, following the  banning of the much despised ivory trade. Conservationists in some areas are now faced with a new challenge: overpopulation. Scientists and conservationists in Africa and globally believe that there are three solutions: translocation, culling or contraception, but there is no one solution which can solve problems of overpopulation immediately, and is problem free and humane.

Late last year, concerned veterinarians, biologists and wildlife experts met in the Netherlands to discuss the way forward in controlling the expansion of wild elephant populations in those areas that face a loss of biodiversity because of large elephant numbers.

Observation and research in areas where large elephant populations have been allowed to naturally grow have shown that elephants are capable of turning woodland into grassland. This means that the species that thrive in wooded areas would be lost from the ecosystem. Wildlife conservationists are then faced with a dilemma - do they conserve elephants at the cost of numerous other species, and biodiversity in general, or do they artificially limit elephant numbers.

The First Workshop on the Control of Wild Elephant Populations reached several conclusions. Current expert knowledge has three main methods of limiting elephant populations in those areas that wish to preserve biodiversity - translocation, contraception and culling.

Translocation, culling

Culling draws strong criticism from all quarters and is no longer extensively practiced. A moratorium on culling has been in place in South Africa since 1994. A decade later elephant populations have doubled in places such as Kruger Park to over 13000. According to, a 7% increase in numbers has conservationists very concerned not only for the vegetation, but the problems associated with elephants wandering outside of the park to surrounding communities, in search of food.

Translocation, while producing valuable knowledge into elephant society, is now becoming a limited option as there are few remaining places that can accommodate elephants successfully in the long term that have not already been utilised.

Contraception is another big contender for controlling elephant populations. Much research has gone into finding an effort to find a safe, reliable and cost effective method of contraception. Limited trials have shown positive results.


Since 2000, the elephant population of the Greater Makalali Private Game Reserve has been managed entirely through contraception of the female elephants found on the reserve. Today there are 66 elephants roaming around the 2500 ha reserve, with 23 of the 28 females of reproductive age being treated with a yearly contraceptive injection.

Unlike human oral contraceptives, the drug used to stop the elephants from reproducing does not rely on sex hormones. Rather, it uses proteins extracted from eggs produced by female pigs. When injected into elephants along with an immunologically enhancing substance, these proteins (known as porcine zona pellucida proteins) successfully stop sperm from binding to, penetrating and fertilising the egg produced when an elephant cow ovulates.

This method of contraception is known as immunocontraception, as it relies on the elephant creating an antibody to the pig proteins. This antibody is what stops sperm from penetrating the egg. The method has been used in 35 species, such as horses, and was first tested on zoo elephants.

In 1996, the first field trials of the vaccine were carried out in the Kruger National Park (KNP), a large undertaking which involved three phases. Initially 41 female elephants were darted, radio collared and injected with the contraceptive vaccine. These were then monitored, and captured again a year later to check for pregnancy. A relatively high contraception rate was achieved, but this was improved on in the next phase of the trial when the elephants were treated with an initial vaccination followed by two booster shots.

With the success of the KNP trial, Makalali was chosen to be the scene of the fourth trial. Makalali was chosen for the trial as it had a habituated elephant population that contained animals that had been individually identified in the past. The challenge at Makalali was to find out if the contraceptive vaccine could be successfully administered to free-roaming elephants and furthermore, if the vaccine could control population numbers.

The study was also designed to see, over a longer period of time than possible during the initial trials, how the elephant's social behaviour was affected by the vaccine.


Four years down the road, the behavioural monitoring research undertaken by Audrey Delsink has thoroughly demonstrated the success of elephant contraception in a small game reserve. For the first three years, the elephants were darted with the contraceptive by people on foot or in a vehicle. Special darts that were designed to fall out shortly after hitting the animal were used, and then retrieved to check that the animal had received her complete dosage.

In the first year an elephant receives the treatment, it is given three separate doses of the vaccine. In following years, only one dose is needed every 12 months.

All the sexually mature cows were darted, regardless of whether they were pregnant or not. Previous work in Kruger had shown that the vaccine has no effect on pregnancy irrespective of the gestational stage nor the mother or foetus. The elephants were then tracked using dung and spoor to identify herds, and individual animals identified by their tusks and ear patterns (holes, nicks, tears and veins in the ears).

The research has shown that the biggest impact the contraception has had on the herd behaviour is that the elephants start to avoid the darting vehicle that usually carries the person who administers the contraceptive while the vaccination programme is in progress. This avoidance behaviour stopped approximately one to two weeks after the last vaccine had been administered.

Previous attempts at elephant contraception using drugs based on steroidal and sex hormones had led to bull elephants severely harassing females, which made them separate from their herds and even their calves.

As the vaccine displays no side effects to gestation or birth, the elephants that first received the contraceptive when they were already pregnant all safely gave birth to healthy babies. Only one calf died as a result of an unexplained attack from a bull elephant.

From August 2002 to January 2004, no new elephant babies have been born on the reserve. None of the female elephants appear to be pregnant, although some of the cows have displayed oestrous and its associated behaviours with mating episodes been witnessed since they were administered the immunocontraceptive.

"Based on the study conducted at Makalali, elephant immunocontraception has thus far been proven to be a safe, reversible and effective means of population control within small reserves, concludes Delsink.

However, the experts agreed that more information is needed on the long term effects of contraception, especially in such social animals. The current costs and logistics of contraception on large populations are one of the main areas that researchers are focusing on.

Another drawback of contraception is that while it can slow down or stop an elephant population's growth rate, it does not actually reduce the number of elephants in those areas that are already overpopulated, such as some areas of Zimbabwe. Which brings the debate back to culling. The Netherlands workshop concluded that "the only realistic way of bringing the population under control is culling" in the areas where the number of elephants is so large. If coupled with a contraceptive program that helps stabilise populations in the long term, culling could then be prevented in future years.

More information:

Article by Melissa Wray, courtesy of Kruger Park Times and edited by Science in Africa.

Related articles:

Living with Elephants

Tracking the illegal ivory trade

Is your ice cream bad for elephants?

Conserving Addo's elephants - the past, present and future of the population

Elephants get a chilli reception

Elephants as giant, rural cash cows

Thieves are plundering our heritage


Science in Africa - Africa's First On-Line Science Magazine

Return to Home PageReturn to the TopYour FeedbackRegister with "Science in Africa" 

Copyright  2002, Science in Africa, Science magazine for Africa CC. All Rights Reserved

Terms and Conditions