Puzzle 25

John Baez

Q: Why do zookeepers give orangutans and other endangered species birth control pills?

A: Because there isn't enough room in zoos, and it's deemed unsafe to return these animals to their native habitat. Breeding animals in zoos is done in a controlled way to reduce the problem of inbreeding and maximize genetic diversity.

But sometimes things go wrong. Edward M. Eveld of the Kansas City Star writes:

Gazing at the chimpanzee hill at the Kansas City Zoo, visitors see chimps doing chimp things, climbing on trees, grooming each other, roughhousing.

It looks so natural, and that's the point.

What visitors might not realize is that the chimp boys and girls are allowed to hang out together in captivity because of something unavailable in the wild: contraception.

In February the zoo celebrated the birth of an eastern black rhinoceros, the first baby rhino at the zoo in 3 1/2 years. Much celebration and a naming contest followed. Such hoopla might lead one to think zoos were working overtime to get their animals to breed.

Mostly, the opposite is true.

"In some regards, it's easier to breed animals in captivity than to keep them from breeding," said Kirk Suedmeyer, director of animal health.

Zoos are getting better and better at the latter. They are tweaking human-style birth control, including the pill and hormone implants. They're trying out birth-control vaccines. And they're helping to develop other methods, such as contraception-laced feed for the hooved animals.

To make it possible for the lions at the Kansas City Zoo to stay together in one big happy pride, Suedmeyer performed tubal cauterizations on the two females, Donna and Jean. The pride, led by Dumisani, includes Jean's three offspring: Nala, Mufasa and Simba. The idea is that the procedures could be reversed if more lion babies were ever needed.

The idea and the hope, that is. As with many animal contraception methods, there are many unknowns.

"It's a technique developed for people, and we're applying it to animals," Suedmeyer said. "Sometimes it's not the same."

Birth control wasn't a big issue when animals were kept in cages. But zoos now prefer naturalistic exhibits, allowing animals to display behaviors typical in the wild. With more social interaction among the animals, the contraception challenge grew.

For one thing, zoos can't accommodate lots of extra babies.

"There's only so much space," said Liz Harmon, the Kansas City Zoo's general curator.

Methods such as neutering and spaying are discouraged because they're irreversible, can alter behavior and have side effects. Zoos still use gender separation as a means of birth control, especially for species in which contraception has been less successful.

In some situations, birth control simply isn't needed. The giraffes in the Kansas City Zoo's Africa area are all females. The gorillas are males.

The chimpanzees, however, are good candidates for birth-control pills or implants. In the Kansas City troupe, seven chimps are on the pill and one has a contraceptive implant. When the implant expires, Suedmeyer said, that female will be switched to pills.

The implants are effective but pose some problems. Suedmeyer places the implant in a chimp's back, so the animal won't bother the sutures needed to close the incision. But troupe mates sometimes find the sutures and try to pull them out. The same has happened with a pair of tamarins, with the male monkey trying to take the implant out of the female.

Suedmeyer has inserted a few extra stitches elsewhere, away from the implant incision, as a distraction.

"We tried to outwit them a little bit, but it doesn't work," he said.

The pill isn't foolproof either. Chimps are crafty at hiding a pill under their tongues and spitting it out later. Or, if the pill is added to their food, it can be difficult to know that they've eaten it all and received a full dose.

The St. Louis Zoo got a shock last month when keepers discovered that Merah, an orangutan on daily birth control pills, was pregnant.

Ironically, the zoo in St. Louis is the national headquarters for animal contraception.

"Yeah, I was pretty proud," said Ingrid Porton, co-director of the Wildlife Contraception Center, which serves the more than 200 accredited zoos in the American Zoo and Aquarium Association.

Porton suspects the pregnancy was not a failure of the pill but a "delivery failure." Typically a staff member crushed the pill in yogurt or honey and watched Merah put it in her mouth. Then she was given a chaser, more yogurt or a drink, to ensure everything got swallowed. It's possible, though, that she shared some of the food with her youngster.

"My suspicion was that she didn't get the full dose every day," Porton said.

While the pill and implants are highly effective, they are not 100 percent. Porton said that a chimp in North Carolina named Ruthie is famous in animal contraception circles for getting pregnant no matter what method keepers try.


Finite exhibit space isn't the only reason to keep animals from getting pregnant. Genetic diversity is also a biggie.

With a fairly fixed number of animals at the nation's zoos, officials want to avoid inbreeding. Successive inbreeding can produce genetic mishaps, which can result in health problems and death.

"Very few animals come in from the wild now," Harmon said.

Computerized records keep the history of captive animals and their ancestors. Family trees are developed to show the relationships among animals.

By controlling who's breeding with whom managers can increase offspring among family lines poorly represented in the zoo population and reduce offspring from animals already well represented.


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