African elephants face two terribly contradictory threats: In some parts of the continent the animals are being hunted into extinction for their valuable ivory tusks, but in other countries elephants are so heavily overpopulated that they pose a threat not just to themselves but to entire ecosystems.

South Africa faces the latter problem. There are now more than 18,000 elephants in the nation—too many to fit into the increasingly smaller territories in which they have been confined. Too little space means not enough food, and hungry elephants have been known to strip a habitat of every piece of edible vegetation, killing all local plants and leaving nothing for other animals to eat. If rapidly growing populations are not controlled, South Africa says it might need to once again start widespread culling of its elephant populations. South Africa stopped culling in 1994 but put the option back on the table in 2008. It has not yet put it back into practice.

But culling is not the only solution. For the past 16 years South Africa has been experimenting with elephant birth control. Female elephants are darted with an immunocontraceptive—porcine zona pellucida vaccine (PZP)—that blocks sperm reception and is said to be between 95 and 100 percent effective. The drug lasts for about a year and treated elephants receive an annual booster. The vaccine is nonhormonal, so it has no behavioral side effects and is also harmless to any males who are accidentally darted.

The Humane Society of the United States has endorsed PZP and posted this video about its benefits:

The contraceptive method received its broadest testing at Tembe National Elephant Park in KwaZulu–Natal Province beginning in 2007. The 300-square-kilometer game reserve was home at the time to about 80 adult female elephants whose birth rates have since dropped to a manageable level, according to a report in South Africa's Mail & Guardian. The park did not disclose the new birth rate, but PZP use on two private reserves in KwaZulu–Natal has kept the elephant populations there stable for the past 12 years, according to a report in Pretoria News.

Tembe epitomizes why the contraceptive method is desirable. The animals that live there used to migrate between South Africa and Mozambique but they are now confined to the reserve for their safety. Migration would normally allow overpopulated herds to spread out and redistribute individuals. That option is no longer available for most elephants.

With the success at Tembe and the two private reserves under its belt, KwaZulu–Natal Province is now planning to expand use of the contraceptive to other locations. "Slowing the growth rate will allow time to be gained to achieve other biodiversity objectives, such as land expansion, without having to cull the elephants," Catherine Hanekom, an ecologist for Ezemvelo KZN Wildlife, told Reuters.

(Contraception isn't the only alternative to culling. Kruger National Park, which is home to more than 14,000 elephants, has a relatively stable population size because the parks agency closed several watering holes, an action that both reduced the pregnancy rate and resulted in the natural die-offs of young calves. The annual elephant population growth rate in Kruger was 6.5 percent but that has dropped now to 2.4 percent and continues to decline, a spokesperson told the Mail & Guardian.)

Slowing births could have a side benefit: the reduction of illegal ivory entering the black market. Conservation experts theorize that the 2008 sale of ivory from culled elephants (a one-time event allowed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora) is responsible for the dramatic rise in illegal ivory sales and elephant poaching over the past few years. Fewer births would eliminate the need for culling, which would also reduce the size of tusk stockpiles from dead animals. A smaller quantity of available tusks, in turn would mitigate the desire of some African nations to try to legalize ivory sales once again.

Ultimately, elephant conservation will absolutely require the use of some form of population control if these massive, emotional and matriarchal animals are going to survive, and contraception is dramatically better than culling. Improved population control will also be healthier for elephant population dynamics, as culling leaves any surviving members of a herd traumatized and untrusting of humans. In addition, young elephants that grow up without adult role models also have a greater likelihood of becoming dangerous rogues. (They have even been known to attack and kill rhinos.) Elephants are never going to have more room in which to roam, so for now at least, this could be the best option available.

Photo: A family of elephants at Kruger National Park, South Africa. By John Savage via Flickr. Used under Creative Commons license