TULSA, Oklahoma - The Tulsa Zoo is mourning the loss of one of its chimpanzees, a press release said Wednesday.

According to zoo staff, an altercation broke out Saturday between the 20-year-old Alvin and the other chimpanzees in the group.

The male chimp was separated from the group and was immediately examined and treated by the veterinary staff, the release said.

The incident occurred during zoo hours, and once Alvin was safely isolated, the interior exhibit was closed to the public.

Alvin had several severe lacerations to his hands, feet and other defensive wounds. He was still responsive to his keeper staff and was eating and drinking normally. He took the antibiotics and pain relievers offered to him in fruit juices.

Once it was determined the chimp had stabilized and could safely undergo anesthesia, zoo veterinary staff did a full examination Monday. The chimp was treated for injuries to his hands, feet and abdominal areas and remained stable while under anesthesia. Afterward, he was given medication for pain and was kept under close observation, the release said.

Early Tuesday morning, Alvin appeared to be sleeping and was breathing normally. Later in the morning, Alvin stopped breathing and zoo staff immediately administered CPR and cardiac rescue medications.

Alvin did not respond to resuscitation efforts and died. He spent his entire life at the Tulsa Zoo.

Results from the necropsy show that the chimp had heart disease and evidence of some kidney function impairment. Cardiac disease is one of the leading causes of mortality for adult and geriatric-aged chimpanzees, according to Dr. Kay Bauckues, Tulsa Zoo veterinarian.

"We were surprised that cardiac lesions were present, as Alvin would only be considered middle-aged for a chimpanzee," Backues said in a statement.

"The stress of the events and his injuries were just too much. His injuries were severe, but survivable, had it not been for his heart condition."

The cause of the altercation has been attributed to a female chimp that had recently come into estrus – or began a normal ovulation cycle -- which created a shift in the delicate chimpanzee social dynamic.

Recently, the Tulsa Zoo was given approval by the Association of Zoos & Aquarium's Species Survival Plan for Alvin to breed with Jodi, mother to 5-year-old female chimp, Vindi. This was the first normal cycle for Jodi since she gave birth to Vindi five years ago.

The social and hierarchical interactions among chimpanzees are very dramatic and at times can be quite volatile, especially when competition arises, zoo officials said.

"Chimpanzees are very powerful animals that at times can demonstrate compassionate and nurturing behaviors and at other times can be very aggressive." said Pat Murphy, primate curator, said in the statement. "These behaviors are instinctual and are observed in both wild and zoo populations."

"We've been very fortunate to have such a cooperative, amicable group of chimpanzees, so this was a really unexpected occurrence. The loss of Alvin is really sad for the entire zoo."

The zoo has two males, 25-year-old Morris and Alvin's son, 4-year-old Bernsen. The remaining chimpanzees include females Jodi, Susie, Hope and Alvin's daughter, Vindi.

"This is a tragic loss, but is also a powerful reminder that these are indeed wild animals with wild instincts," Backues said. "Though it may seem brutal, this type of behavior is still part of a chimpanzee's nature, even in a zoo environment."

Two other deaths at the Tulsa Zoo made news in recent years.  A giraffe died after injuring its neck during transportation in December 2009, and a second giraffe died of hypothermia in January 2010.