A zoo is facing criticism from animal rights activists after an Asian elephant died - 25 years after he sustained a leg injury while in captivity there. Rama the elephant, who completed paintings with his trunk, died Monday, Oregon Zoo officials announced on Facebook. He was 31. 'Rama had experienced a sharp decline in mobility in recent weeks, an issue stemming from a 25-year-old injury to his left front leg,' the zoo said in the post. Scroll down for videos . Missed: Rama the elephant was euthanized this week at the age of 31 by Oregon Zoo officials. His leg was injured after female elephants shoved him into a moat in 1990 . Skill: Rama used his trunk to create paintings, which reportedly earned over $100,000 in sales . It continued 'The treatments that had been successful for many years were no longer easing his discomfort, and so — with sadness and compassion — our animal-care staff decided the most humane course of action was to euthanize him.' The elephant's 32nd birthday would have taken place on Wednesday. Studies vary on how long Asian elephants live in captivity. A 2008 study which looked at Asian elephants in European zoos says they have a median life expectancy of 19 years. A 2004 study indicated a 36-year median for Asian elephants in North America. Zoo veterinarian Jim Storms said in a release on the Oregon Zoo's website that Rama's 2013 tuberculosis diagnosis did not play a role. Deputy Director Chris Pfefferkorn said in the release the leg injury took place in 1990 as Rama was sexually maturing. He said in what is considered normal activity for the animals, older female elephants shoved Rama out of the herd and into a moat. Courtney Scott, a leader of the protest group Free the Oregon Zoo Elephant, told KOIN 'He shouldn't have been put in a herd with adult females when he was young. I think that is a grave error on the part of the zoo and just shows what happens when elephants live in zoos.' Artwork: One of Rama's paintings - made by using his trunk - is seen here . Friendship: Rama (left) is seen with female elephant Chendra . Memories: Rama is seen in this 1991 photograph, one year after his leg was injured . 'Well, Rama sustained the injury before any of the folks that work here were here,' the zoo's elephant curator Bob Lee countered in an interview with KOIN. He went on 'They made the best decision they could at the time. They were trying to give Rama the opportunity to stay in that herd situation.' Scott also told the television station that Oregon Zoo doesn't have enough room to hold the elephants. Zoo staff, however, told KOIN construction on a larger elephant enclosure is underway. Lee told the television station 'Rama was a really special elephant. He had strong bonds with the folks that worked with him, to the community. 'We had a lot of people that would come out every Sunday and watch him paint. We had a lot of people that grew up with him.' Zoo officials said Rama's paintings have been showcased by the Mark Woolley Gallery. One woman, Calley O'Neill, painted with the elephant for five summers, KPTV reported. According to the television station, Rama's solo paintings have made over $100,000. Rama's work with O'Neill can be seen at the website forThe Rama Exhibition. O'Neill told KPTV 'There's no elephant on Earth that has ever done or ever will do such magnificent abstracts.' Debate: Elephant activist Courtney Scott (left) has claimed Oregon Zoo officials should not have placed Rama with female elephants at a young age. Elephant curator Bob Lee (right) has said zoo officials 'made the best decision they could at the time'
Rama the elephant, who completed paintings with his trunk, died Monday, Oregon Zoo officials announced on Facebook .
Zoo officials said Rama's leg was hurt in 1990, when older female elephants shoved him out of the herd and he went into a moat .
They said Rama was euthanized after health problems from the leg injury .
Elephant group Free the Oregon Zoo Elephants has claimed zoo officials should not have placed Rama with the females at a young age .