NEW YORK » On a gray day in mid-June, at the edge of a leafy enclosure in the Bronx Zoo’s Wild Asia habitat, an elephant named Happy stood very still, gazing over the fence. There were a few logs scattered around, some grass and shrubs, and a concrete-lined pool. A green ball was marooned at the water’s edge.

Visitors snapped photos from the monorail that circles the exhibit, while a guide cheerfully reported Happy’s age (44) and her weight (8,500 pounds). A recorded voice noted the plight of elephants in the wild. Then the monorail swept past, and the visitors turned their attention to the rhinos in the next yard, unaware of an increasingly heated dispute over Happy’s fate.

For close to a decade Happy has lived alone, separated from the zoo’s two other elephants. Her solitary existence is quite unlike the life of a wild elephant. In nature, elephants live in closely bonded matriarchal families, which cooperate to raise their young. Females never leave the herd, forming lifelong attachments with siblings, cousins and aunts as well as with their mothers.

Happy’s predicament has caught the attention of wildlife rescue organizations and animal advocacy groups, including In Defense of Animals, which has named the Bronx Zoo one of the "10 worst zoos for elephants" for three years in a row, largely based on Happy’s isolation. There is a petition making the rounds on the Internet calling on Mayor Bill de Blasio to order a study on her health and well-being, and another (which has collected nearly 87,000 signatures) asking the zoo to release Happy from "solitary confinement."

The feud over Happy is awkward for the Bronx Zoo – and really for every zoo – because it opens up a larger and more volatile debate: Is it right to keep intelligent and behaviorally complex animals like elephants in captivity?

Indeed, nearly a decade ago, the Bronx Zoo made a conscious decision to end its elephant program, opting to shift its resources to help endangered elephants in the wild. It would not bring in any more elephants to replace the ones that had died, and would eventually move some other animal into the elephant habitat. But what to do with the zoo’s last three resident elephants – particularly Happy, who had no partner – became a vexing problem.

Happy was captured as a baby, probably from Thailand, in the early 1970s, along with six other calves, possibly from the same herd. The seven elephants, named for Snow White’s seven dwarfs, were shipped to the United States and dispersed among various zoos and circuses. Happy and Grumpy landed in the Bronx in 1977.

For the next 25 years, Happy and Grumpy lived together. The zoo had other elephants, all kept not in one group but as in Noah’s ark, two by two. In July 2002, however, Happy and Grumpy were placed in an enclosure with another pair, Maxine and Patty. Patty and Maxine charged at Grumpy, who stumbled and fell. Her injuries didn’t heal, and that October, when she could no longer get up, she was euthanized.

Happy, with her lifelong friend now gone, was paired with a younger female named Sammy (whose companion had also died a few months earlier). The two seemed to bond, according to a zookeeper at the time, who insisted on anonymity to avoid alienating former colleagues.

"Happy had been subordinate and shy," she said. "But she stepped into a mother role with Sammy, so it worked out really well."

But Sammy developed severe liver disease, and she, too, was euthanized, in early 2006 – the third Bronx Zoo elephant to die in just four years. A week later, James J. Breheny, the zoo director, announced that the zoo would phase out its elephant program.

"Certainly Sammy’s death made us re-examine what we were doing with the elephants," Breheny, who is also executive vice president of the Wildlife Conservation Society, the zoo’s parent organization, said in an interview this month.

At the time, the Association of Zoos and Aquariums, the industry’s trade group, was encouraging zoos to create a "breeding group," with at least one male and several reproductive females (a more natural social world for the animals, and one that might keep zoos supplied with adorable baby elephants).

But that would have required a new elephant habitat and barn, at a cost of $80 million or more, Breheny recalled. It seemed too much to spend on an exhibit that is open only from May through October.

"For us as a conservation organization," Breheny added, "it was better to put these resources into protecting elephants in the wild."

The zoo would keep its three remaining elephants; it would reconsider if one of them died. But in the aftermath of Sammy’s death, it seemed too risky to place Happy with the others, who had charged her companion. So in her 30th year at the zoo, as she entered middle age, Happy was alone.

Critics Say Zoo Is Cruel

Most visitors to the Bronx Zoo’s well-tended compound would be alarmed to hear that it is being accused of substandard care. This is no dusty roadside tourist trap: The Wildlife Conservation Society was a favorite charity of Brooke Astor’s, and last year had an operating budget of $235 million. The society is a leader in elephant conservation efforts through its 96 Elephants campaign and employs some of the top wildlife researchers working in the field.

And yet critics contend that with all its expertise and resources, the conservation society could do better for its own elephants. Later this summer, People for the Ethical Treatment of Animals plans to file a complaint with the Association of Zoos and Aquariums on behalf of Happy and 15 other elephants housed alone or in pairs. Delcianna Winders, a lawyer for the PETA Foundation, argues that keeping just one or two elephants is not only cruel, it also violates the trade group’s own professional standards.

"These zoos should be stripped of their accreditation," she said. "Otherwise accreditation is meaningless."

The association requires zoos to keep at least three female elephants (or two males) and to have a certain amount of space in which they can roam. PETA is arguing that while the Bronx Zoo meets the letter of those regulations, it violates their intent by keeping Happy separate.

PETA and other advocates, as well as the former zookeeper, would like to see Happy released to a wildlife sanctuary, where she could live among other elephants in an environment closer to their natural habitat. There are two such facilities in the United States – the Elephant Sanctuary in Hohenwald, Tennessee, and the Performing Animal Welfare Society (PAWS) in San Andreas, California. Each occupies more than 2,000 acres of woods and pasture, with lakes and ponds for bathing. Both sanctuaries have taken in elephants that once lived in zoos – including the zoos in Detroit, San Francisco, Toronto, Cleveland, Anchorage, Alaska, and Madison, Wisconsin.

Breheny isn’t interested in following that path. Happy, he said, is "very well adjusted and, I would say, has deep bonds for the people who care for her." During the day, Happy stays in a separate yard; at night in the barn, she has a separate stall. But the three elephants are able to see one another over the fence, and sometimes the barn door between them is kept ajar. "The keepers report that she’s totally content," Breheny said. "Their reading of her is that she’s happy."

Though Happy spends much of her time alone today, she was briefly a celebrity in the scientific world, the star of a study in animal cognition. Most animals show no interest in their own image, but when three scientists placed a mirror in the holding yard at the Bronx Zoo in the summer of 2005, Happy looked in the mirror and noticed a mark that had been painted on her head, and touched it repeatedly with her trunk. She seemed to understand that she was looking at herself.

Until then, only the great apes, dolphins and humans (starting around 18 to 24 months) had passed the test, which, the authors of the study wrote, "is thought to correlate with higher forms of empathy and altruistic behavior." (More recently, magpies have joined the club.)

Diana Reiss, a professor of psychology at Hunter College and one of the authors of the study, said that all these species, from human babies to elephants, go through the same stages as they explore the mirror, and all show an interest in looking at parts of their bodies they cannot otherwise see, like their eyes.

"To me, it links us all in a fundamental way," Reiss said.

For Toni Frohof, a wildlife behavioral biologist who has studied elephants and dolphins for more than 20 years and works with In Defense of Animals, the study makes Happy’s story especially poignant.

"She exhibits self-awareness, yet one of the most important aspects of her psychological and physical life, the ability to be around other elephants, she’s been deprived of," Frohof said.

Challenges of Captivity

Standards of care at the Bronx Zoo have changed over the years, as awareness of animal abuse has increased. In the 1980s, the elephants were sometimes dressed in costumes and were trained to perform tricks – practices that would be frowned on today. And while "aversion training" with pointed bullhooks was once the norm, today the zoo uses the sort of positive reinforcement methods you might use with your dog: Lift a foot for the vet, get a treat.

But while certain practices can be changed, some experts argue that elephants simply cannot thrive in zoos. The celebrated primatologist Jane Goodall has said as much, and last year Scientific American published an editorial calling for the end of captivity for elephants.

Elephants, of course, are not the only sentient creatures confined in zoos. But their intelligence and sociability make them a particularly troubling case. As any child knows, elephants have remarkable memories. They also use tools, cooperate to solve problems and communicate in a language of more than 70 distinct sounds. If an elephant is ill, family members may try to lift him with their trunks and tusks. And when one elephant dies, the others mourn – researchers have observed a whole herd gather around a dead comrade, touching her with their trunks, and brushing soil and placing branches over her body.

The intense kinship of a large, multigenerational pachyderm family is not easily replicated in a zoo, and has never existed in the Bronx, at least not since the time when mastodons roamed the region. And compared with a natural range that can extend for hundreds of square miles, the Bronx Zoo’s habitat seems woefully cramped. The New York City climate is not ideal for elephants either.

With limited space and no infants to care for, captive elephants can become catatonically bored. A great majority of elephants in U.S. zoos – as much as 85 percent, according to a 2013 study by the Honolulu Zoo – develop disturbing neurotic behaviors, such as repetitive swaying and head-bobbing. The Bronx Zoo denies that any of its elephants manifest these behaviors, but according to the former zookeeper, she and other keepers have observed Happy, Patty and Maxine swaying and bobbing, both in their enclosures and on recorded monitors.

In spite of the clamor for moving Happy, the zoo is confident that she is better off staying. Breheny has been at the zoo even longer than Happy: He started working there part time as a teenager in 1973 and never left (though he took time from his duties to earn bachelor’s and master’s degrees).

"To take her from everything that she knows, and bring her to a strange place and expose her to other individuals – there’s no guarantee she’s going to get along with the other elephants," Breheny said. "She could, but she might not."

In any case, Breheny says that if the zoo were to move her, it would probably choose another accredited zoo, rather than a sanctuary. "A lot of these places are built by a couple of passionate, dedicated individuals," he said. But he suggested that a sanctuary might lack long-term financial stability. "We know we have the facility and the resources to manage them and to manage whatever we may encounter as we shepherd them into old age," he said.

The association likewise prefers elephants to stay in its network, rather than go to sanctuaries, which by definition are not eligible for membership in the group. "When they go to an AZA-accredited zoo, we know exactly what kind of care they’re going to get," Robert Vernon, a spokesman for the association, said. "At sanctuaries, there’s a lot that we don’t know and frankly can’t control."

The association in the past has used its power to compel compliance: Three years ago, as the Toronto Zoo prepared to send its two elephants to PAWS (a move that was affirmed only after a rancorous court battle), the association revoked the zoo’s accreditation. The sanctuary transfer was cited as the reason.

Such custody disputes have left both zoos and sanctuaries feeling bitter. Margaret Whittaker, director of elephant care at the Elephant Sanctuary in Tennessee, says she would like to mend fences. "We very much want to partner with zoos," she said, "and work together toward elephant welfare."

Several animal advocates interviewed for this article proposed a way to reconcile. In PETA’s perfect world, "accredited zoos would shift to a sanctuary model," Winders suggested, explaining that they would "take in the tens of thousands of animals that are in roadside zoos, or living as pets in people’s living rooms and backyards."

Whittaker described what a sanctuary zoo might look like: "Huge space, the opportunity for natural foraging, and an environment that supports the social structure that elephants need."

Adam Roberts, head of the advocacy group Born Free USA, adds one more requirement: no more imports of elephants from the wild.

"Born Free envisions a future in which the only zoo is a rescue zoo," he said. "It’s essentially turning these facilities into sanctuaries for animals that are in need of lifetime care, rather than animals that have been bred or imported for a lifetime of captivity."

Should She Stay or Go?

So where does this leave Happy? Her former keeper says she still hopes that the zoo will relent and send her to a sanctuary. Introducing a new elephant to a group, even gradually, can be tricky. But Ed Stewart, co-founder and president of the PAWS sanctuary in California, said he had never had a new elephant that couldn’t be integrated into the group. "Just give her the option," he said.

Whittaker says that if Happy came to Tennessee, she could spend her last years living a little closer to how an elephant is meant to live.

"Maybe Happy could find a friend in somebody here," she said.

Late in the afternoon on the same gray day in mid-June, in the hidden back entrance to the elephant exhibit, two zookeepers emerged from a barn, carrying large plastic buckets of fruits and vegetables. From this vantage of the exhibit, on the opposite side of the monorail, there were no shouting children, nobody taking pictures.

Happy was standing some distance away, in a grove of trees. A zookeeper called her name, and she came strolling over, remarkably graceful. The keeper handed her lettuce leaves and apple slices. She took each piece in her velvety trunk, which she curled daintily toward her mouth.

The keeper demonstrated how Happy responded to voice commands. "Get over," he said gently, and she moved to the side. "Foot," he said, and she put her foot on the fence rail. "Speak," he said, and after a pause she made a soft rumbling sound.

But on the subject of where she would like to live, and if she often feels lonely, she was silent.

N.Y. Times Editors’ Note: June 29, 2015 : An article last Sunday described the debate over the treatment of Happy, an elephant at the Bronx Zoo who lives separately from the zoo’s two other elephants, which animal-rights groups claim is cruel. After the article was published, editors learned that the writer had signed a petition on the website change.org that called upon the zoo to release Happy to an elephant sanctuary. Such involvement in a cause related to news coverage is at odds with The Times’s journalistic standards; if editors had known that the writer had signed the petition, they would not have assigned the article to her.

CORRECTION: An earlier version of this article misstated the reason the Toronto Zoo lost its accreditation from the Association of Zoos and Aquariums. It was because the Toronto City Council, rather than zoo professionals, made the decision to transfer its elephants to a sanctuary; it was not because the elephants were moved. The article also erroneously included Cleveland in a list of cities whose zoos had sent elephants to sanctuaries.

© 2015 The New York Times Company