The last 50 chimpanzees owned by the National Institutes of Health are headed to Chimp Haven—a federally funded sanctuary in Keithville, Louisiana.

The retirement plan, announced on Wednesday, comes two years after the agency decided to phase out chimp research following a report that found such research unnecessary. At the time, the agency said it would set stricter requirements for primate research and retire most of its 360 chimps, hanging on to only 50. Those remaining chimps were set aside in case researchers needed them in special circumstances, such as emergency studies during a public health crisis.

But since the 2013 decision, no proposals to use the chimps have moved forward. And, in June of this year, the US Fish and Wildlife Service granted chimps endangered-species protection, which meant that researchers would need to apply for permits to conduct invasive chimp research.

In an interview with Nature, NIH director Francis Collins said the decision to retire the last 50 “is the natural next step of what has been a very thoughtful five-year process of trying to come to terms with the benefits and risks of trying to perform research with these very special animals.” In that time, he added, the need for chimp research shrank to zero.

While some researchers have expressed disappointment and concern for future research, particularly Ebola studies, animal welfare advocates welcomed the news. In fact, the agency’s decision comes just weeks after Collins himself was targeted by the People for the Ethical Treatment of Animals (PETA). In a letter delivered to people in the Washington, DC area, PETA accused Collins of abusing baby monkeys, revealed his home address, and encouraged people to confront him.

The process to transfer the chimps to Chimp Haven could take several years, pending space availability at the sanctuary.