A wave of fresh outrage spread across the globe in March after the Copenhagen Zoo — now infamous for killing a healthy 18-month-old giraffe just over a month ago — culled four lions to make room for a new male who they hope will start a new pride. But even more than outrage, the killings have spurred conversation about how best to control animal populations in zoos.

European zoos like the one in Copenhagen often favor euthanasia when a population gets out of control or becomes too genetically similar, which puts the animals at risk of inbreeding. Zoos in Europe don't have the range of options that American zoos have when it comes to moving animals to other locations that are more suitable. Many of them argue that euthanizing some animals is often better for the population as a whole because it allows grown animals to rear their offspring to a point. Copenhagen Zoo is against birth control because it prevents animals from acting as they would in the wild.

American zoos, by and large, favor contraception. Birth control may keep animals from breeding for a time, but they argue that it is better to prevent breeding than allow an animal to be born when the zoo knows it will soon have no room for the animal.

"In Copenhagen Zoo we let the animals breed naturally," the zoo said in a statement posted on its website when officials killed Marius the giraffe. "That means that the animals get to carry out their natural behaviors. Parental care is a big part of an animal’s behavior."

Later, zoo officials added, "Contraceptives have a number of unwanted side effects on the internal organs, and we would therefore apply a poorer animal welfare if we did not euthanize.”

This means Copenhagen Zoo prefers to let its animals live as natural a life as possible in captivity — free of birth control. However, this allows for the birth of animals that the zoo may not have room for — or that may put the population at risk of inbreeding — and often results in euthanasia. The Copenhagen Zoo euthanizes around 30 animals per year.

Image: POLFOTO, Peter Hove Olesen/Associated Press

The European Association of Zoos and Aquariums, the governing body for those establishments across Europe, defended the zoo's choice to kill the lions in a statement on its website:

The zoo has been consistent in its approach to animal-population management and high standards of animal welfare. Copenhagen Zoo takes an approach that good welfare in the pride is stimulated and enhanced by natural cycles of reproduction, and that cub-rearing is an essential part of pride activity. As a result, while EAZA regrets the death of the animals in question, we recognize the right of Copenhagen Zoo to humanely cull them in line with their policies.

The zoo, which did not respond to our request for comment, was trying to make room for a new male lion that would lead a younger pride and mate with two young lionesses. Two of the lions killed were older, and the zoo said those lions would have tried to kill the new male because they would perceive him as a threat to their established pride. The other two euthanized lions were cubs. According to zoo officials, the new male would have killed the cubs because male lions typically eliminate all sexually immature young that aren't their own offspring when they establish control of a new pride.

The reasoning is scientifically sound. The young lionesses are the offspring of one of the older lions, and keeping the older lion around would have risked inbreeding. The new male assures genetic diversity.

Zoo officials in the United States told Mashable they understand the scientific validity of how the Copenhagen Zoo operates, and that, logically, it is best to cull a few animals for the good of the larger number. But U.S. officials also said they feel that the Copenhagen Zoo is failing to grasp how the public reacts to euthanasia of healthy animals.

"We're zoos; we're in the public eye," said Rick Barongi, director of the Houston Zoo. "If we say we care for animals and we have the highest standards of care, you can't euthanize them."

Others have questioned the reasoning behind the Copenhagen Zoo's euthanasia policy. Heather Robertson, a senior veterinarian at the Nashville Zoo, said modern contraception doesn't necessarily decrease an animal's quality of life.

"You look at all these years we've spayed and neutered dogs or controlled populations in that way for more domestic animals, and I don't think there's a decrease in the quality of life," Robertson said. "I understand what they're saying, because you're taking [away] that naturalistic drive that they would have. But with non-permanent controls, you can reverse that and put them back in a breeding state."

The Association of Zoos and Aquariums, which oversees those American organizations, did not respond to a request for comment, but it has been quick to point out that euthanasia is a last resort in the United States.

In a statement on its website, it said: "The Association of Zoos and Aquariums regrets the unfortunate incident at the Copenhagen Zoo involving the death of a giraffe. Incidents of that sort do not happen at AZA-accredited zoos and aquariums for several reasons."

Those reasons are in part because AZA-accredited zoos "carefully manage breeding programs," according to the site, and American zoos have a "well-developed" animal exchange program that ensures the animals will have a home elsewhere.

Image: David J. Phillip/Associated Press

Still, Barongi and Robertson acknowledge that finding a home for animals is more difficult for European zoos because regulations there prevent the zoos from transferring animals to private owners or zoos that are suitable but not accredited by an overseeing organization.

"I don't think they have as many options over there. But, that said, they should be creating options and be proactive," said Barongi, adding that he respects the Copenhagen Zoo's conservation program.

Barongi hopes zoo officials address the euthanasia issue at the World Association of Zoos and Aquariums meetings that will take place this coming May and November.

For its part, the WAZA issued a somewhat contradictory statement after Marius the giraffe was killed, saying it recognizes that euthanasia can be necessary to control populations, but that it should be used "only as a last resort."

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