Izzle, Timon, Batman, River and Mars spent years confined to inside of a lab, their lives devoted to being tested for the benefit of human health.

But these rhesus macaques have paid their dues and have settled into retirement. The monkeys can now amble around in larger enclosures that let them venture outside, eat lettuce and carrots, paint and hang from pipes and tires.

Researchers say that more labs are retiring primates to sanctuaries like Primates Inc., a 17-acre rural compound in central Wisconsin.

While most research facilities need to euthanize primates to examine their tissues, technological advances, such as brain scans, mean fewer monkeys need to be put down.

Researchers are also making more efforts to give the ones who can survive a retirement, rather than euthanization.