"People's traditional expectation of zoos is that they see lions and tigers and elephants," zoo Director Ron Kagan said. "But it's also their expectation that an animal has a good life."
Accordingly, Winky and Wanda will be sent to one of two U.S. refuges this summer or early fall.
Wanda is taking anti-inflammatory medication for chronic arthritis in her front legs; Winky has foot problems, likely related to sleeping in a standing position -- an unnatural one for elephants, who sleep on soft surfaces in the wild.
In the wild, female Asian elephants like Winky and Wanda typically roam 30 miles a day, form lifelong and unique friendships with members of their herds and mourn for their dead.
The Detroit Zoo "is the first to make a purely voluntary decision of this nature," said Wayne Pacelle, chief executive officer of the Humane Society of the United States.
Five U.S. zoos have closed elephant exhibits in recent years under public pressure after animal deaths or alleged mistreatment.
Celebrity Couples of 2014 [PHOTOS]