Rama, a critically endangered Sumatran tiger, died recently at an Indonesian zoo notorious for the high death rate of its charges. Once celebrated as the oldest and largest zoo in the country, the Surabaya Zoo has earned a new reputation: “death zoo.”

The most recent tiger death involved heart failure, said zoo spokesperson Veronika Lanu, according to Agence France Presse. “The death was due to natural causes—we provided the best care we could,” she said. Rama had issues with his teeth, a bad cough, and appeared lethargic in the weeks before his death, AFP reported. Tigers can live for 20 years in captivity.

It’s unclear what truly led to the tiger’s death, but critics of Surabaya say it’s in keeping with a long pattern of abuse and neglect. Specific concerns cited include overpopulation, as well as cramped and trash-ridden cages. In a petition, People for the Ethical Treatment of Animals has called for officials to shut down the zoo immediately.

View Images A veterinarian observes Sumatran tigers at Surabaya Zoo, where a tiger named Rama died recently—sparking controversy. Photograph by Robertus Pudyanto, Getty Images

But Surabaya isn't the only zoo out there facing harsh criticism for mistreatment of animals. Which begs the question: What makes a good zoo?

To some people there’s no such thing—a wild animal simply shouldn’t be confined in this way. Ethical considerations around keeping elephants, in particular, in such tight quarters are hotly debated (one investigation found that the infant mortality rate of elephants in U.S. zoos was almost triple that of elephants in the wild). But if an animal is under a zoo’s care, how can we distinguish the more responsible from the negligent?

One way is to check zoo-accrediting organizations and their standards. Most well-known American zoos, for example, are accredited by the Association of Zoos and Aquariums. The bar for becoming a member of the association is set higher than the standards for obtaining a license from the United States Department of Agriculture, a requirement for all zoos in the country. But some critics question whether even the AZA rules are too lax.

In general, zoos that demonstrate the following qualities shouldn’t raise a red flag.

Conservation mission: Traditionally zoos have prized their animals solely for their entertainment value, displaying them in tiny cages. While some zoos still focus purely on entertainment, others conduct research, help to conserve wild animals by breeding them for reintroduction into the wild, and educate the public about the animals and their conservation status.

“Zoos have tried to change their mission, and some have done that better than others,” Daniel Blumstein, chairman of the department of ecology and evolutionary biology at the University of California, Los Angeles, told the Guardian last month. “The onus is on zoos to show an educational mission, to have a potential to do more than entertainment.”

For example, the San Diego Zoo has 132 conservation projects in 62 countries, ranging from breeding the rare alala bird for reintroduction in Hawaii to monitoring gorillas in Cameroon.

Animal welfare: Of course, a decent zoo meets animals’ basic needs: appropriate food, fresh water, proper exposure to light. Animals have enclosures that are clean, roomy enough—for flying or running, swimming or climbing—and include features that mimic conditions in the wild.

View Images An elephant gives herself a sand bath in 2013 in a spacious enclosure in the Smithsonian Institution's National Zoo, in Washington, D.C. Some people think that elephants, in particular, shouldn't be confined in zoos at all. Photograph by Ricky Carioti, The Washington Post, Getty Images

But a higher-quality zoo goes beyond meeting the bare necessities. “An institutional commitment to ensuring that each animal is thriving, not just surviving,” should be the fundamental philosophy of a good zoo, according to the framework laid out by Detroit Zoological Society’s Center for Zoo Animal Welfare.

One way to do that is by offering enrichment activities or stimulating animals’ minds, said Mike Dulaney, curator of mammals at the Cincinnati Zoo and Botanical Garden. That could mean hiding treats in a container that tigers would have to rip open, for example, or tossing a giant ball into a pool for them to play with. “You try to give them something different every day,” he said.

So how can you tell if an animal is happy? Stressed out animals might have physical injuries or engage in “stereotypic behaviors,” such as pacing or swaying back and forth. One study found that enrichment helps reduce stereotypic behavior only 53 percent of the time, so brain games aren’t a cure-all.

Oversight: A zoo that cares keeps its animals’ records current and provides consistent veterinary care, which the AZA says should at the very least involve twice monthly inspections. “You have to have good and consistent care by professionals trained to deliver it,” said Dan Maloney, deputy director of animal care and conservation at Florida’s Jacksonville Zoo and Gardens, “and have a situation with enough resources so you can make sure it’s delivered in the right way.”

And a better zoo will belong to an accrediting organization, which makes it more likely that higher standards are upheld and that there are consequences for falling short.