Some changes are easy to spot: Enclosures have been expanded. Natural vegetation has replaced concrete. Other changes are more behind-the-scenes: Zoos are teaming up to save endangered species. They’re also devoting millions of dollars to research and focusing on teaching visitors about challenges animals face in the wild.

Such efforts have won praise from many people. But zoo critics say that enclosures are still cages, no matter how many trees are in them. They argue that zoos are inhumane, pointing to studies that have shown that animals in captivity suffer from anxiety, boredom, and stress. Wild animals, the critics say, should be free.

Recently, the debate over keeping wildlife in captivity has grown even more heated. This past February, the London Zoo in the United Kingdom tried to mate two Sumatran tigers, a species that is critically endangered. But the male mauled the female to death before zookeepers could intervene. The incident shocked people around the world and caused many to ask: Have zoos transformed enough to truly benefit animals?

Some changes are easy to spot: Enclosures have been opened up. Natural vegetation has replaced concrete. Other changes are more behind-the-scenes. For example, zoos are teaming up to save endangered species. They are also devoting millions of dollars to research. And they are focusing on teaching visitors about challenges animals face in the wild.

Such efforts have won praise from many people. But zoo critics say that enclosures are still cages, no matter how many trees are in them. They argue that zoos are inhumane. They point to studies that have shown that animals in captivity suffer from anxiety, boredom, and stress. Zoo critics say that wild animals should be free.

Recently, the debate over keeping wildlife in captivity has grown even more heated. This past February, the London Zoo in the United Kingdom tried to mate two Sumatran tigers. That species is critically endangered. But the male mauled the female to death before zookeepers could stop it. The incident shocked people around the world. It caused many to wonder if zoos have changed enough to truly benefit animals.

The earliest known menagerie existed in ancient Egypt more than 5,000 years ago (see Key Moments, above). Modern zoos, which became popular in the early 1800s in Europe, have continued to capture humans’ fascination. That’s because zoos let people connect with wild animals in ways that just aren’t possible through books or YouTube videos, supporters say.

“Most people won’t have the opportunity to travel to Asia or Africa to see orangutans or elephants. But they can visit a zoo and see them up close,” says Rob Vernon of the Association of Zoos & Aquariums (AZA). That group officially certifies zoos that meet strict standards for animal care, conservation, and education.

Just making eye contact with a tiger can leave a lasting impression. “People are much more likely to want to help conserve an animal if they learn about it and see it up close,” Vernon explains.

The earliest known menagerie existed in ancient Egypt more than 5,000 years ago (see Key Moments, above). Modern zoos became popular in the early 1800s in Europe, and they still capture humans’ fascination. That is because zoos let people connect with wild animals in ways that are not possible through books or YouTube videos, supporters say.

“Most people won’t have the opportunity to travel to Asia or Africa to see orangutans or elephants. But they can visit a zoo and see them up close,” says Rob Vernon of the Association of Zoos & Aquariums (AZA). That group officially certifies zoos that meet strict standards for animal care, conservation, and education.

Just making eye contact with a tiger can leave a lasting impression. “People are much more likely to want to help conserve an animal if they learn about it and see it up close,” Vernon explains.

Many of the nation’s best zoos have made it their mission to protect animals, particularly endangered ones. They do that in part by studying the species they house. At the National Zoo in Washington, D.C., research on elephants is helping scientists develop a vaccine for a potentially fatal virus that affects herds in zoos and in the wild.

In addition, the AZA helps coordinate zoos’ efforts to protect more than 500 species. Those efforts include breeding endangered animals and, when possible, releasing them into the wild to help restore dwindling populations. Zoos have helped the black-footed ferret, the red wolf, and a handful of other species recover from the brink of extinction this way, says Ben A. Minteer, a conservation expert at Arizona State University.

Many of the nation’s best zoos have made it their mission to protect animals, particularly endangered ones. They do that in part by studying the species they house. At the National Zoo in Washington, D.C., research on elephants is helping scientists develop a vaccine for a potentially fatal virus. The virus affects herds in zoos and in the wild.

In addition, the AZA helps coordinate zoos’ efforts to protect more than 500 species. Those efforts include breeding endangered animals. And, when possible, zoos release those animals into the wild. This helps restore dwindling populations. Zoos have helped the black-footed ferret, the red wolf, and a handful of other species recover from the brink of extinction this way, says Ben A. Minteer. He is a conservation expert at Arizona State University.

Such efforts may sound noble, but zoo critics argue that many breeding programs focus more on sustaining zoo populations than saving species—and that many animals being bred aren’t endangered. Zoos, critics say, are more concerned with having baby animals, which bring people—and therefore more money—into the parks.

Plus, success stories like the red wolf’s are rare, Minteer says. “Each one of these cases takes an enormous effort—multiple zoos, government agencies, scientists, volunteers. It can take many millions of dollars. Once it’s back in the wild, the animal has to be monitored. It’s a never-ending process,” he explains.

Efforts to breed certain endangered species, such as giant pandas and lowland gorillas, have proven difficult—and, as in the case of the Sumatran tigers at the London Zoo, sometimes deadly. And many animals that zoos can breed successfully, including otters and even songbirds, lack the skills they need to survive in the wild.

Plus, some endangered animals don’t have a natural habitat to return to, says Lori Marino, a scientist who studies animal behavior in Kanab, Utah. “If their natural ecosystem is destroyed, then those animals must remain in captivity their entire lives,” Marino says. “That is not conservation.”

Such efforts may sound noble. But zoo critics argue that many breeding programs focus more on sustaining zoo populations than on saving species. They argue that many animals being bred are not endangered. Critics say that zoos are more concerned with having baby animals. The baby animals bring people, and therefore more money, into the parks.

Plus, success stories like the red wolf’s are rare, Minteer says. “Each one of these cases takes an enormous effort: multiple zoos, government agencies, scientists, volunteers. It can take many millions of dollars. Once it’s back in the wild, the animal has to be monitored. It’s a never-ending process,” he explains.

Zoos have found it hard to breed certain endangered species, such as giant pandas and lowland gorillas. And sometimes the efforts turn deadly, as in the case of the Sumatran tigers at the London Zoo. Zoos can breed many animals successfully, such as otters and songbirds. But those animals often lack the skills they need to survive in the wild.

Plus, some endangered animals do not have a natural habitat to return to, says Lori Marino. She is a scientist who studies animal behavior in Kanab, Utah. “If their natural ecosystem is destroyed, then those animals must remain in captivity their entire lives,” Marino says. “That is not conservation.”

Life in captivity is often difficult for animals, Marino says. Many show signs of stress and boredom. Big cats walk in endless loops. Polar bears rock their heads. Elephants sway. Such repetitive behaviors aren’t seen in the wild, Marino explains: “When you see a tiger pacing, that means it is very stressed.”

One study found that carnivores with naturally large ranges, such as polar bears, lions, and tigers, show the most stress in captivity. Wild polar bears’ home ranges can span 31,000 square miles—about a million times the size of a zoo’s typical polar bear enclosure.

Other research has shown that many animals are intelligent and experience a wide range of emotions. Elephants, for example, can recognize themselves in mirrors. They comfort other elephants that are distressed and grieve when a member of their herd dies. Critics say that knowing animals have such complex feelings should stop zoos from keeping them captive, with little control over their lives.

Life in captivity is often difficult for animals, Marino says. Many show signs of stress and boredom. Big cats walk in endless loops. Polar bears rock their heads. Elephants sway. Such repetitive behaviors are not seen in the wild, Marino explains. “When you see a tiger pacing, that means it is very stressed,” she says.

One study found that carnivores with naturally large ranges show the most stress in captivity. Such animals include polar bears, lions, and tigers. Wild polar bears’ home ranges can span 31,000 square miles. That is about a million times the size of a zoo’s typical polar bear enclosure.

Other research has shown that many animals are intelligent and experience a wide range of emotions. For example, elephants can recognize themselves in mirrors. They comfort other elephants that are distressed. They grieve when a member of their herd dies. Critics say that knowing animals have such complex feelings should stop zoos from keeping them captive, with little control over their lives.

Elephant research has prompted more than 25 zoos in North America to close their elephant exhibits in recent years, sending their herds to sanctuaries with more room to roam.

Sanctuaries resemble animals’ natural environment and range more than zoos do, Marino says. In sanctuaries, “the animals’ health and well-being are a priority. People aren’t getting close to them. They’re getting back as much of their freedom as possible,” she says.

Elephant research has caused more than 25 zoos in North America to close their elephant exhibits in recent years. The zoos send their herds to sanctuaries with more room to roam.

Sanctuaries are more similar to animals’ natural environment and range than zoos are, Marino says. In sanctuaries, “the animals’ health and well-being are a priority. People aren’t getting close to them. They’re getting back as much of their freedom as possible,” she says.

Meanwhile, zoos are exploring new ways to prioritize animals’ needs. In 2011, the Philadelphia Zoo in Pennsylvania introduced a trail system for its animals. Tigers, red pandas, and other creatures cross the zoo overhead in mesh bridges and tunnels that give them more choice in where and when they roam. About 20 zoos worldwide have followed this approach.

And Jacksonville Zoo’s year-old great ape exhibit features several computerized learning stations that allow gorillas to communicate with zookeepers by pressing certain symbols, shapes, and colors. The technology helps reduce boredom and gives the gorillas a chance to have a say in their care. A massive tree at the exhibit’s center houses an area from which the zoo’s staff can study the apes—without intruding into their space.

Meanwhile, zoos are exploring new ways to put animals’ needs first. In 2011, the Philadelphia Zoo in Pennsylvania introduced a trail system for its animals. Tigers, red pandas, and other creatures cross the zoo overhead in mesh bridges and tunnels. This system gives them more choice in where and when they roam. About 20 zoos worldwide have followed this approach.

And Jacksonville Zoo’s year-old great ape exhibit features several computerized learning stations. These allow gorillas to communicate with zookeepers by pressing certain symbols, shapes, and colors. The technology helps reduce boredom. It also gives the gorillas a chance to have a say in their care. At the exhibit’s center, a huge tree houses an area from which the zoo’s staff can study the apes without intruding into their space.

Are such changes enough to make life in zoos positive for animals? The debate over whether zoos are ethical continues. But the upgrades have attracted visitors. U.S. zoo attendance has risen by 20 percent over the past 15 years.

Still, even supporters know that zoos must maintain a delicate balance of keeping their animals happy, giving visitors access to them, and protecting animals from extinction in the wild.

Says Vernon, “Zoos today must exist for a higher purpose.” 

Are such changes enough to make life in zoos positive for animals? The debate over whether zoos are ethical continues. But the upgrades have attracted visitors. U.S. zoo attendance has risen by 20 percent over the past 15 years.

Still, even supporters know that zoos must maintain a delicate balance of keeping their animals happy, giving visitors access to them, and protecting animals from extinction in the wild.

Says Vernon, “Zoos today must exist for a higher purpose.”