Tom Cade, Cornell emeritus professor of zoology, who as an environmental champion worked tirelessly and successfully to save peregrine falcons from extinction, died Feb. 6 in Boise, Idaho. He was 91.

“Throughout his career, Tom was an outspoken advocate for all birds of prey, for science-based solutions in conservation biology, and for tenacious, hands-on conservation actions that produce real results,” said John W. Fitzpatrick, director of the Cornell Lab of Ornithology. “Tom’s no-nonsense character and strong conservation convictions were accompanied by an extremely warm personality and a big, trademark smile. … A great tree has fallen.”

In the 1950s and ’60s peregrine falcon populations steadily declined in the eastern United States. Cade and other scientists discovered that the agricultural use of the synthetic-organic insecticide DDT after World War II was the cause of the bird’s demise.

DDT hindered development of the bird’s eggshell, making it thin and susceptible to cracking – resulting in the death of the young. By 1970, the peregrine falcon population living in the eastern United States plummeted to near zero nesting pairs; the bird was placed on the U.S. Fish and Wildlife Service’s list of endangered species.

Cade joined the Cornell faculty as a professor in 1967, and he directed research at the Lab of Ornithology. Understanding the falcon’s grim prospects, Cornell built Cade a peregrine breeding barn – known as the Hawk Barn – at Sapsucker Woods in Ithaca. There, he initiated an intense program to propagate raptors in captivity and introduce them into the wild. Falconers and birders from all over the nation sent money to support his research; with that, he founded The Peregrine Fund at the lab.

Following the U.S. ban of DDT in 1972, Cade worked to get falcons soaring again in the eastern U.S. By 1975, Cade had placed 16 young peregrines into remote places throughout the Northeast. The number of falcons placed into the wild tripled to nearly 50 by 1977, and tripled again in 1978.

Cade’s program spawned feathered celebrities. After releasing young birds at the Aberdeen Proving Ground in Maryland, one – a falcon named Scarlett – made her way to Baltimore, 30 miles away.

“She made her first appearance at the Baltimore Zoo,” Cade said in 1978. “After feeding on pigeons and starlings there in February, she adopted the 35-story building of the United States Fidelity and Guaranty Co. – an insurance company – as her cliff.”

Soaring around the upper stories, Scarlett thrilled downtown Baltimore office workers with her power and grace. The building – since renamed the Transamerica Building – sits at Baltimore’s Inner Harbor.

Through two decades of work, Cade and his colleagues placed more than 1,600 peregrine falcons all over the eastern U.S.

By 1980, his falcons had begun to reproduce in the wild, east of the Mississippi. The population rose steadily in the 1980s and ’90s. In 1999 the peregrine falcon’s recovery was considered complete, and Bruce Babbitt, the secretary of the U.S. Department of the Interior officially removed it from the endangered species list.

“What an amazing accomplishment – and what a great way to end the 20th century,” said Tim Gallagher, a former editor-in-chief of the Lab’s Living Bird magazine, in his tribute to Cade on the Audubon Society website.

Thomas Joseph Cade was born Jan. 10, 1928, in San Angelo, Texas. He earned a bachelor’s degree from the University of Alaska (1951), and a master’s (1955) and doctorate (1958) at the University of California, Los Angeles.

He is survived by his wife, Renetta, their five children and grandchildren.