Wild Animal Fertility Control In Europe

In Europe, people are interested in reducing certain wild animal populations for various reasons. For example, wild animals can damage crops and forests, spread diseases, cause car accidents, hurt biodiversity, eat farmed animals, and attack people. The public is beginning to oppose killing more strongly, which increases interest in other methods such as fertility control. In some situations, wild animal fertility control is an effective way to decrease populations.

Although the only wild animal contraceptive available in Europe is nicarbazin, several contraceptives have shown promise in wild populations:

• PZP immunocontraceptive vaccines have been shown to lower fertility in horses, donkeys, and certain deer for a number of years. However, in some species, PZP vaccines cause behavioral changes such as multiple infertile estrous cycles, a longer breeding season, possible late births, and changes in social hierarchy.
• GnRH immunocontraceptive vaccines have been tested on wild boar, badgers, wild goats, deer, foxes, squirrels, and prairie dogs. These vaccines eliminate reproductive behavior and can cause potentially painful injection site reactions. 
• ContraPest is a liquid birth control meant to stop rats from ovulating or producing sperm. It must be given every day for at least 50 days to stop rats from having litters. The side effects are unknown.
• EP-1 is a hormonal contraceptive, similar to the hormonal contraceptives humans use, which has been tested on rats.
• Nicarbazin prevents the development of an embryo in a bird’s egg.

Contraceptives can be given to animals in two ways: through an injection (which can be done by hand or remotely) or through bait. If a contraceptive is delivered as bait, a specially designed bait delivery device must be used to make sure that the contraceptives don’t get eaten by animals that aren’t meant to eat them.

In general, the author argues, killing seems to be more effective than fertility control. However, these results don’t generalize to all situations. For example, if infertility causes breeding pairs in monogamous species to break apart, then fertility control will be more effective than it would be in lab settings. Conversely, if killing animals causes wild animals from other populations to immigrate to the newly depopulated area, it will be less effective than it seems to be in lab settings.

The author points out that killing doesn’t actually work to reduce human-wildlife conflict in many populations, and fertility control is another tool that wildlife managers can use in those situations. For example, in several European countries, rat poisons are actually losing their effectiveness, which makes it crucial to shift away from rodenticides and towards alternative methods of population control such as contraceptives. Killing animals also disrupts their social arrangements, which leads to more contact between individuals and more disease transmission.

Fertility control can prevent human-wild animal conflicts in ways other than reducing populations. For example, it can be used to maintain populations at a particular size or to prevent diseases transmitted mother-to-child. If wild animals are troubling humans by building nests or performing other reproductive behaviors, fertility control gets rid of the behavior without killing the animal. Fertility control can also be more effective for disease eradication because it increases the percentage of the population that is vaccinated.

The cost of fertility control depends on the cost of materials and people to deliver the contraceptives, and creative approaches can help to reduce costs. For example, volunteers might deliver contraceptives. 

Finally, killing animals has negative side effects. Beyond the moral implications of taking the lives of animals (something the author doesn’t mention), it’s dangerous to use guns in cities and other populated areas. Rodenticides harm the environment, such as by poisoning non-target species.

Several contraceptives have the potential to control wild animal populations without killing them, although only one is available in Europe. Although killing animals is widely believed to be more cost-effective than fertility control, fertility control may in fact be more cost-effective in certain situations. To advance the use of non-lethal contraceptives, advocates should push for the development and approval of new and more effective contraceptives, as well as further research into their understudied side effects.