Shirley, who had a twin sister, Jean, earned a bachelor’s degree from Royal Holloway, University of London, where she studied Latin and French, and a master’s from the school in teaching education.
She began a career largely teaching languages in schools and colleges in the United States, France and Australia, and later received a second master’s from the University of Illinois, Urbana-Champaign, in French literature. Then, in 1971, she received her Ph.D in education from the University of Cincinnati.
She accompanied her husband, an engineer, to New Delhi, where he worked on a National Science Foundation project, and then to Thailand, where he had a job with the United Nations. It was there that Ms. McGreal encountered the infant macaques at the airport.
“She became very concerned with their welfare and did research to see who was doing what to whom in the animal trade,” Mr. McGreal said in a phone interview. “Her interest in them happened in an instant.”
After starting the International Primate Protection League in 1973 with Ardith Eudey, a primatologist (who would remain an adviser until her death in 2015), Ms. McGreal became known for her willingness to help other conservation groups financially and for her worldwide network of people who alert her to primates in life-threatening situations and identify smugglers.
“We’ve been amazed that someone didn’t kill her,” said Lois K. Lippold, a primatologist who runs a foundation to protect the douc langur monkey and is on the league’s board. “She’s gotten death threats, and they just steel her even more. It takes a certain kind of person to do what she does because the picture is so grim for primates everywhere.”
Dr. Lippold said that Ms. McGreal rallied many others in the primate conservation world to write to the prime minister of Vietnam five years ago to persuade him not to commercially develop part of a forest in Da Nang where doucs eat.