When that petition failed, another petition popped up Monday, titled, "Fire Bengt Holst From the Copenhagen Zoo For Having Marius the Giraffe Killed." It had more than 16,000 signatures as of 3:30 p.m. ET.

Zookeeper and TV personality Jack Hanna, who is also director emeritus of the Columbus Zoo and Aquarium in Ohio, joined the chorus of outrage Monday, calling the Copenhagen Zoo's decision "the most abominable, insensitive, ridiculous thing I've ever heard of."

He also questioned why the Copenhagen Zoo would keep breeding animals for which it didn't have room. The Columbus Zoo would never put down an animal in this manner, Hanna said, and he wouldn't condone showing an animal consume another animal to children.

"I know it's natural in nature. I'm not an idiot," he said, "but I don't need to have some 2- and 3- and 6-year-olds -- they cannot understand at that age. You understand they don't understand nature. They haven't been to Africa, so that's what we do at the zoos. We try to educate people at zoos on what happens in the wild."

Which is exactly what Holst argues the Copenhagen Zoo was doing. As for exploring other purportedly more humane options, such as lethal injection or sterilization, Holst said that an injection would have contaminated about 200 kilograms of perfectly good meat, which was out of the question. He added, "if we just sterilize him, he will take up space for more genetically valuable giraffes."

Options deemed not viable

Several zoos volunteered to take Marius. The UK's Yorkshire Wildlife Park, which said it has the capacity for an extra male, was among several places that offered to take him.

Copenhagen Zoo said in a Q&A about the decision on its website, "it is not possible to transfer the giraffe to another zoo as it will cause inbreeding."

The EAZA's Dickie said some institutions were ruled out because they did not meet her organization's strict protocols, and the Copenhagen Zoo wouldn't send Marius to an institution with "lesser standards of welfare."

She further said that while EAZA members are "saddened by the death of any animal in our care," the EAZA supports the Copenhagen Zoo's decision and reiterated the zoo's claim that "transfer within our network does not represent a solution to the unsuitability of the individual animal for breeding."

In the EAZA's history, which dates to the early 1800s, its member zoos have put down only five giraffes, Dickie said.

Numerous American zoos did not immediately respond to requests for interviews. The Association of Zoos and Aquariums declined a request, issuing a short statement from executive director Kris Vehrs stating that EAZA's "programs and procedures vary from those of the AZA."

"Through the AZA Species Survival Plan program, these methods include science-based breeding recommendations and cooperating to plan for adequate space," Vehrs said in the statement.

The Woodland Park Zoo in Seattle, Washington, also declined an interview but said its birth plans were managed by the AZA Species Survival Plan.

"With each new animal birth, Woodland Park Zoo establishes a breeding and relocation plan that ensures a healthy and genetically sound future for the individual and species," the statement said.

To claims that the Copenhagen Zoo acted irresponsibly by allowing Marius to be born if it had no room to house him, Dickie said the giraffe was born more than two years ago, and it's difficult to predict "genetic kinship" and a zoo's available space that far out.

As for preventing the giraffes from breeding, that would violate the EAZA's standard of "providing a behavioral repertoire as natural as possible" for animals in captivity, she said.