Immunocontraception is gaining popularity amongst
conservationists for use in populations of
charismatic megafauna. Charismatic megafauna are populations of animals that are tremendously destructive, but people are reluctant to
cull the populations because they're
cute. This is called
Bambi syndrome. An excellent example of this is the
White-tailed Deer. A survey of homeowners for a certain town found that nearly 100% of residents felt the deer problem was unacceptable, but less than a third supported killing the deer. Another example is in Australia, specifically on
Snake Island where the
koala population has grown too large for the island to support.
Immunocontraception works by pitting the animal's own immune system against its reproductive system. It is sometimes called the "pregnancy vaccine". The process involves capturing females of the species and injecting them with modified porcine ova. Because ova do not belong in the bloodstream, nor under the skin, the animal's immune system treats them as invading cells and produces immune antibodies to destroy them. This means that when the animal next goes into estrus, the creature's own immune system will destroy the ovum before it can be fertilized.
Trials have found the procedure to be acceptably effective, a year after a population is treated, only 20% of the treated females were pregnant, in comparison to 80% of the untreated. This has been used on a wide variety of species, from coyotes to elephants to koalas to deer. Similar efficacy rates are found across the species.
The procedure is not foolproof, however. Researchers have found that sterilized females live longer than unsterilized ones. The procedure also works better in monestrous species, animals that only go into heat once a year. Deer are an exception to this case, in that if the deer does not become impregnated, she will go into another heat cycle. This has had the effect of prolonging the rut season. This is a problem for people because rut season is when deer are crossing streets, and causing accidents. Additionally, the species should be long-lived, or you must go out and retreat the entire population every two years or so. To complicate matters further, the vaccine must be species-specific. If an American Bald Eagle or other endangered species takes a treated prey animal, and becomes sterile as a result, then that is obviously a problem.
The final drawback is one of cost. Presently the animals must be captured and treated, and occasionally recaptured later for a booster shot. Work is being done on a new vaccine that requires no booster. At some point in the future, a formula will likely be developed that can be put into a dart gun, bringing the cost of treating a population to nearly the same level as killing off the excess members.