Marius the giraffe died on Feb. 9 from a shot to the head with a bolt gun. Workers at the Copenhagen Zoo then publicly dissected the animal and fed his body to the lions.

News of the incident horrified people worldwide, and the zoo faced backlash that included death threats to the zoo's director, Steffen Stræde.

This week the Copenhagen Zoo is making headlines again after it euthanized four healthy lions — two adults and their 10-month-old cubs — by lethal injection.

In an interview with the Ritzau news bureau, Stræde said the zoo didn’t expect a public outcry like it received in the wake of Marius' death.

"I think people are more enlightened after Marius," he said. “Marius hasn't made us the least bit afraid because what we are doing is the most correct thing to do."

To understand the rationale behind his comments, you have to understand the history.

Euthanasia vs. contraception

Zoos have a responsibility to maintain diverse populations of animals for the health of the species, but they have limited capacity. Therefore they're faced with two controversial methods to regulate those populations: birth control or euthanasia.

U.S. zoos choose contraception, and the Saint Louis Zoo's Wildlife Contraceptive Center researches animal contraception and advises zoos on birth control methods.

Various forms of contraceptives have been used in more than 600 species, including pills, IUDs and vasectomies. Chimpanzees take human birth control pills, giraffes consume hormones in their feed, and grizzly bears receive slow-releasing hormones implants.

Cheryl Asa, director of research at the Saint Louis Zoo, told the New York Times in 2012 that contraception is a better fit for U.S. zoos than euthanasia.

"On an emotional level, I can’t imagine doing it (euthanasia), and I can’t imagine our culture accepting it," she said.

But zoos that belong to the European Association of Zoos and Aquariums subscribe to the idea that birth control disrupts animals' natural behavior.

"We have already taken away their predatory and anti-predatory behaviors," Bengt Holst, the Copenhagen Zoo's conservation director, told the New York Times. “If we take away their parenting behavior, they have not much left."

Holst said his zoo euthanizes 20 to 30 healthy exotic animals annually.

Zoos like Copenhagen allow their animals to mate as they normally would, have offspring and raise their young until the age at which they'd naturally leave their parents.

At this point, the zoo steps in and euthanizes the offspring whose genes are already present in the population.

According to this line of thinking, allowing Marius — a giraffe whose genes are common — to live in any zoo takes space away from an individual that could enhance the species' genetic diversity.

This has been cited as a possible reason why the zoo euthanized Marius despite offers from other zoos to take him.

Genetic diversity is important to a species' survival because it prevents inbreeding and preserves a variety of traits that animals might need to survive.

What's more natural?

The debate over euthanasia versus birth control centers on what constitutes a more natural life for animals in captivity.

European zoos that practice euthanasia argue that parenting is one of the few natural behaviors zoo animals are allowed.

A statement on the Copenhagen Zoo's website reads, "Parental care is a big part of an animal's behavior. It is a 24-hour job in longer periods of their lives, and we believe that they should still be able to carry out this type of behavior also in captivity."

They say euthanizing surplus offspring mimics what occurs naturally in the wild, where not all young survive.

Critics say such measures could be detrimental to certain populations. In 2012, the Copenhagen Zoo put down two leopard cubs whose genes were overrepresented even though the International Union for the Conservation of Nature lists the cats as near threatened.

Euthanizing healthy offspring also raises other questions. Critics have said it's suspicious to kill recently matured animals, given that baby animals are a major zoo attraction.

European zoos say contraception isn't a better alternative to euthanasia because in addition to preventing the natural behaviors of parenthood, it also puts the animals at risk.

Just like in humans, birth control has side effects. Large cats on hormonal implants can be more susceptible to tumors, and elephants have experienced difficulty restarting their reproductive cycle when they come off contraceptives.

Despite these complications, U.S. zoos say using birth control does allow for more natural behaviors because it permits animals to live in natural social groups instead of being segregated to avoid mating.

Preserving such natural groups is another reason the Copenhagen Zoo permits animals to be euthanized.

The four lions that were recently put down were killed to make way for the introduction of a new young male lion.

The zoo said the 3-year-old lion wouldn't have been accepted by the pride if the older, 16-year-old male were alive.

"Furthermore we couldn't risk that the male lion mated with the old female as she was too old to be mated with again due to the fact that she would have difficulties with birth and parental care of another litter," the zoo told The Associated Press.

The cubs were also put down because they were not old enough to fend for themselves and would have been killed by the new male lion anyway, zoo officials said.
 

While euthanasia is allowed under the American Zoo Association, it's typically reserved for sick or elderly animals.

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