William J. L. Sladen, a physician by training and zoologist by choice who became a leading expert on the libido of Antarctic penguins and the migratory patterns of endangered birds in North America, died on May 29 at his home in Warrenton, Va. He was 96.

The cause was cerebrovascular disease, his wife, Jocelyn Sladen, said.

While much of Dr. Sladen’s work was conducted in frigid anonymity, two apogees of his research were popularized — in “Penguin City,” a television documentary first broadcast by CBS in 1971, and in “Fly Away Home,” a 1996 Hollywood film starring Jeff Daniels and Anna Paquin.

Dr. Sladen (pronounced SLAY-den) was a technical adviser to “Fly Away Home,” a fictionalized version of his joint venture with William Lishman, an artist and pilot, to teach young Canada geese, swans and other birds to fly safe migratory routes guided by an ultralight aircraft in the lead position of their traditional “V” formation.

Many birds migrate instinctively. Others need to be taught. Dr. Sladen and Mr. Lishman found that orphaned birds whose parents were unable to teach them to fly could be guided from breeding grounds to winter refuges, and would remember how to get home and to make the round trip the next year.