Globus, the rare, gentle Amur tiger who appeared on the cover of National Geographic and fathered the popular cub, Billy Ray, born last year, is dead.

The 14-year-old, wild-born Russian cat was euthanized Aug. 13 by the Pittsburgh Zoo & PPG Aquarium veterinary staff after tests determined his long-term kidney problems had worsened and he was in renal failure. He didn't respond to a variety of medications and, at the end, had lost interest in eating even the fresh salmon that keepers and veterinarians bought special for him and that he had loved.

Globus was old but not as aged as some of the other animals at the zoo in Highland Park. But together they are part of a national trend that has seen zoo animals live longer, and, just like humans, need more medical treatment, medications and therapy as they near the end of their lives.

The lengthened lives of animals in captivity has been abetted by the increased attention zoos now pay to healthier food, modern medicine, more natural habitats and social environments that reduce stress and result in more robust animals.

"Yes we are seeing our animals live longer," said Dr. Barbara Baker, the Pittsburgh zoo's president and chief executive officer. "In 1982 when I started here, a lot of zoos didn't even have full-time veterinary care.

"Now we're seeing situations where the level of care has increased, the animals are living much longer and we're having to deal with animals that have more geriatric problems."

The zoo's animal population has been getting younger overall due to recent births of sea lions, beavers and other species, but it still has a number of animals that might qualify for an AARP card. Around the corner from the tiger exhibit at the Highland Park zoo, Shiba, the 20-year-old female lion, and Juma, a male a year younger, move arthritically through their rocky exhibit and receive regular analgesic medication. The life expectancy for lions in captivity is 20 years.

And up the hill at the bear exhibit area, Rocky, a Kodiak with arthritis in his hind legs so bad that zoo visitors notice, soaks in a circulating pool, part of a twice weekly hydrotherapy regime. That and the pain medicine he's administered seem to help him walk better. He's 26 -- old for a bear.

Steve Feldman, a spokesman for the Association of Zoos & Aquariums, said its accredited members are committed to lifetime care for their animals, and have pushed the longevity envelope for many species.

That care includes preventative medical assessments, including daily observations and data recording, routine weight monitoring, full physical examinations including blood and fecal testing, dental examinations, diet supplementation and vaccinations. That helps in early detection and treatment of illnesses and diseases.

"All the advances in medical care for humans are mirrored in advances for animals and that has kept them alive and healthy much longer than in the past," Mr. Feldman said. "That's a testament to the animal-care professionals, our veterinarians and keepers, who are able to maintain animals into old age by using medical techniques, new drugs and even alterations to exhibits."

Pittsburgh zookeepers altered the gorilla exhibit space by building a walkway this summer for Zakula, a wild-born female who is 42 or 43 years old, either age making her the oldest of the zoo's 4,000 animals. She's been in at the Pittsburgh zoo for more than 20 years, mothered three babies and has arthritis severe enough that she often doesn't want to go out when it's raining.

"Gorillas can live until they're 50, but a lot don't," said Karen Vacco, who recently took over as assistant curator of mammals after being primate keeper and lead keeper for 18 years. "Do I expect her to be around much longer? No. It's a hard reality for us, but she's still having a fantastic summer."

Zakula's imminent mortality has brought back memories for Ms. Vacco of the summer five years ago when the zoo's male silverback gorilla, Mimbo, and its male orangutan, Mr. G, both died of old age complications. The silverback died naturally; Mr. G was euthanized.

"I've seen a lot of primates born and die here," she said. "They're so much like us, and I'm with them more than my family. They become a big part of my life and I treat them as though they're part of the family."

And sometimes as with humans, even with the best of care and seeming to be in good health, animals die.

That's what happened two years ago when Chica, a Whooley monkey who was more than 30 years old, died suddenly. She had been drinking the dietary supplement Ensure and held the longevity record for her species in captivity.

"She was old but doing fine health-wise, until one day out on exhibit while swinging from branch to branch she seemed to stumble and died," Ms. Vacco said. "It turns out she had a heart attack. But it's what we hope for. She went quickly and didn't suffer. The zoo visitors didn't even realize what had happened."

But modern medicine is producing better outcomes and longer lives for many zoo animals. Arthur, a 16-year-old binturong, an obscure, tree-dwelling species from the rainforests of Sumatra and Borneo that's commonly known as an Asian bearcat, is housed in the Kid's Kingdom section of the zoo. His cage bears the sign, "Don't give Arthur any treats. He's a diabetic and on a strict diet."

"He started losing weight two years ago and peeing more," said Judy Obeldobel, lead keeper at the zoo. "We did a physical and discovered he was diabetic. Now he gets an insulin injection every day and is given less of the fruit he would normally eat in the rainforest and more almonds, pecans and olives to control his blood sugar. He's doing well."

That was not the case for Globus, a personable tiger with a lot of fans at the zoo. He'd been coughing and lethargic. He was sedated and X-rayed to allow Dr. Stephanie James, the Pittsburgh zoo's new director of veterinary service, to look at his lungs, kidney function and joints.

"He didn't have pneumonia but he was in end stage renal failure -- his kidney function was shutting down," said Dr. James, who came to Pittsburgh from the Bronx Zoo in New York and knew Globus when he was in the tiger exhibit there. "We played with his medications for a month, trying antibiotics and steroids and attempting to increase his appetite."

Nothing worked for long. At the end, he wouldn't get up, wasn't interested in eating. Dialysis wasn't an option.

"He got scruffy and skinny," Dr. James said. "We were at the end of our rope for what we could do medically."

The zoo's Animal Management Committee, including Dr. James, Dr. Baker and the keepers and staff who knew Globus best, convened to make the very hard decision.

"It was a huge effort. Everyone was involved from the keepers to the director, and it was the group's decision that it was time for Globus," Dr. James said. "Every time I have to make that decision it's the biggest responsibility I have to face as a professional, and it's done with great care and compassion."

The day for the euthanization was selected and the keepers were notified so they could spend time with the tiger if they wanted to. With the veterinary staff in attendance, Globus was shot with a dart containing an anesthetic to immobilize him.

Once he was asleep, Dr. James removed his testicles to determine if they contained sperm, then administered a barbiturate through an intravenous hookup, and he never woke up.

"Globus was a valuable genetic animal for the species survival plan and we wanted to do what we could to save his genetics," she said, adding that some tissue from Globus was also taken and is being preserved at the San Diego Zoo. "Unfortunately he had no sperm. He was too sick. But we wanted to do everything we could."

All end-of-life decisions are hard and that was especially true for Globus, whose following was long and stretched to the zoo president's office.

"It wasn't just that Globus was a beautiful tiger. He also had a great personality, very laid-back and easygoing," said Dr. Baker, who recounted how, after a mourning dove flew into a window in the tiger exhibit and was stunned, Globus padded over, picked it up in his mouth and gently laid it on a rock in the sun.

"He was so gentle and unique but at the end there wasn't a darned thing we could do for the fella."