(CHICAGO) A popular, longtime resident of Lincoln Park Zoo, Molly the Amur tiger was euthanized this week because of failing health from advanced age.

The zoo was “saddened to report that on Aug. 17, animal care staff made the difficult but humane decision to euthanize Molly, a geriatric female Amur tiger,” a statement from the zoo said.

Born at the North Side zoo on Nov. 16, 1997, Molly spent her entire life there except for three years, and was a favorite among her keepers and zoo visitors.

“Despite her age, Molly would frequently roam her habitat and powerfully vocalize, much to the enjoyment of both staff and guests,” zoo general curator Dave Bernier said in the statement. “Over the years, Molly developed very strong, trusting bonds with her keepers and most enjoyed her time quietly lounging or exuding her playful side.”

But things started going downhill in the last few weeks.

“Molly had increasingly exhibited evidence of age-related discomfort and illnesses, which veterinarians monitored and treated frequently to ensure continued health and well-being,” the zoo statement said.

“Recently, however, her health and quality of life rapidly deteriorated due to advanced age.”

Molly, 18, was the second-oldest female Amur tiger in captivity in the United States, according to the statement. Median life expectancy in captivity is just under 14 1/2 years.

She was one of several geriatric residents of the zoo, part of a nationwide trend.

“With advancements in zoo medicine, nutrition, research and husbandry techniques, animals are living longer in zoos and aquariums around the nation, posing new challenges and creating advancements in animal care,” Bernier said in the statement.