The zoo dilemma

Cheryl Asa,who directs the Association of Zoos and Aquariums Wildlife Contraception Center at the St. Louis Zoo,said euthanasia was not a comfortable fit for zoos here. On an emotional level,I cant imagine doing it and I cant imagine our culture accepting it, she said.

Asa sees contraception as a better approach. By preventing the birth of animals beyond carrying capacity, she said,more animals can be well-cared for.

But in Europe,some zookeepers would rather euthanise unneeded offspring after they mature than deny the animal parents the experience of procreating and nurturing their young.

Wed rather they have as natural behaviour as possible, said Bengt Holst,director of conservation for the Copenhagen Zoo. We have already taken away their predatory and anti-predatory behaviours. If we take away their parenting behaviour,they have not much left.

So he and many of his European counterparts generally allow animals to raise their young until an age at which they would naturally separate from parents. It is then that zoo officials euthanise offspring that dont figure in breeding plans.

This spring,the Copenhagen zoo put down,by lethal injection,two leopard cubs,about 2 years old,whose genes are already overrepresented in the collective zoo population. Leopards are considered near threatened by the International Union for the Conservation of Nature. But as part of a breeding plan to maintain the genetic diversity of this species,the cubs fate was determined before they were born.

The Copenhagen zoo,he said,annually puts to death some 20 to 30 healthy exotic animals from gazelles,to hippopotamuses,and on rare occasions even chimps.

The thinking is that this strategy mimics what would have occurred in the wild,where some 80 percent of feline offspring die from predation,starvation or injury,he said.

International guidelines on the ethics of breeding zoo animals have been elusive,in part because societal philosophies vary,said Dave Morgan,chairman of the Population Management Committee at the World Association of Zoos and Aquariums.

US zoos began developing contraception for highly fertile animals like lions in the 1970s,after breakthroughs in human birth control. Contraception use then expanded as it became quite difficult for zoos to sell or give away animals they could no longer accommodate.

This kind of family planning meant males and females no longer had to be kept apart to avoid unwanted pregnancies. There were benefits,too,for zookeepers: Hormones in contraceptives given males can take the edge off aggressive behaviours surrounding competition for a mate.

There was a time when no one could have imagined that contraception would be needed for the Mexican wolf,a species hunted nearly to extinction in the 1970s. Zoos began with only seven survivors and bred a captive colony of nearly 300 wolves,saving the species. Ninety-two were reintroduced into the wild starting in 1998,but then four years ago,the US government used up the limited space that had been allotted for the program.

So,for the last four years,birth control has helped the zoos breed selectively to maximise genetic diversity but not run out of holding space or Mexican wolves.

Genetic diversity is key to long-term species survival because it prevents inbreeding and preserves a broad array of traits that animals need to survive in the wild.

Contraceptive science for most exotic animals,Asa notes,is not as advanced as for apes,which are more closely linked to humans. And side effects can and do occur. Large cats and canines on early hormonal implants were susceptible to uterine infections and tumours. Other animals like elephants have trouble restarting their reproductive cycle once they come off birth control.

European countries on the other hand embrace the euthanasia policy and are open about educating their public. A few years ago at Zoo Magdeburg in Germany,it was discovered that a male tiger was a hybrid of two tiger subspecies,rendering the cubs it had sired genetically useless. When the three cubs were born,the zoo euthanised them immediately.

Even when zoos wait to euthanise animals until their parents have had a chance to raise them,questions can come up. It might seem suspiciously convenient for zoos to destroy an animal just after it has completed its most adorable phase given that baby animals are a top zoo attraction.

But Holst emphasized that the timing is dictated by nature. Zookeepers know it is time when the young leopards start picking fights with their mother.

It may be painful for us, he said,but more natural to them.