Some of the work of Dr. Birdwhistell, an anthropologist who retired as a professor of communication from the University of Pennsylvania in 1988, seemed to be just good fun - such as when he pronounced Walnut Street the "smile capital" of Center City.
That was in 1972, after he and a group of researchers conducted a "smile survey" at busy intersections at Walnut, Chestnut and Market Streets. Between Walnut and Market, the smiles dimmed, the researchers found.
"Of course, we're not certain, but it does appear that Walnut tends to be a place of more leisurely noontime activity," he told a reporter at the time. ''The pace is fast on Market. Also, there are more strangers on Market. . . ."
But smiles were not a trivial pursuit for Dr. Birdwhistell, an associate of Margaret Mead's. He did much of his research at the Eastern Pennsylvania Psychiatric Institute.
By the time he was measuring those Philadelphia smiles, he already had studied grins from the Great Lakes to Alabama. He found that greater smiles didn't necessarily mean greater happiness.
"Southerners think they're friendlier because they smile, and New Englanders think they're more reserved because they don't, but I'm not sure either is true," he said.
People tend to smile the way their neighbors do, he said.
Peculiar to Philadelphia, he noted, was the "so-called Main Line smile, particularly in the female, where teeth almost protrude beneath the upper lip. That gave rise to the term, the 'horsey' look."
In fact, he told an interviewer in an article for the New York Times Sunday Magazine: "There are no universal gestures. As far as we know there is no single facial expression, stance or body position which conveys the same meaning in all societies."
Dr. Birdwhistell was a slender 6-footer, with gray hair and a lined face that easily broke into a smile, a deep bass voice, and a comfortable manner that quickly put others at ease.
He was a man of many interests.
As a youth, he played football until he broke his ankle in high school, and all his life he enjoyed watching body movement in games of all kinds - especially the graceful moves of basketball players, his wife said. Julius Erving was a favorite.
He also was involved with human rights, from the 1930s until the 1970s, his wife said. He visited the coal mines in Harlan County, Ky., with Eleanor Roosevelt and helped integrate the University of Louisville, in the late 1940s and early 1950s.
He also collected first editions of Mark Twain, Walt Whitman and William Blake, and enjoyed fishing, gardening and wood-carving. He learned to repair Oriental and Navaho rugs and often took "eating trips" to try barbecue spots throughout the South.
Born in Cincinnati, Ohio, he graduated from Miami (Ohio) University and Ohio State University before earning a doctorate at the University of Chicago.
His fascination with body language began in 1945, when he was doing a field study of the Kutenai Indians in Western Canada. He noticed the Indians' facial expressions and gestures differed depending on whether they spoke English or Kutenai.
After that, he said, he began looking at universal gestures, body language that was common to all cultures. And though he found none and strongly believed there were none to be found, he had learned to read the body language that often reveals much about how people feel, even if they say nothing at all.
To uncover those hidden signals, Dr. Birdwhistell spent much of his research time in a laboratory examining films of personal interactions, frame- by-frame, to analyze the body motions of the participants.
So thorough was he, that he broke the motions down into component parts to analyze them. In the face alone, he looked for meaningful clues in seven areas - scalp, eyebrows, forehead, eyes, nose, lips and chin - and developed a shorthand notation for each.
In some cases, those studies simply helped people understand the subtle messages they respond to every day in dealing with others. Sometimes, they were used to help therapists understand the unspoken feelings among family members, for instance.
He learned that body language could be used to show that even therapists don't know as much about themselves as they think they do, he recalled in the 1972 interview.
He cited one instance of a therapist who believed in being completely nonauthoritative in group therapy sessions. Yet, through prompts as subtle as a glance or a finger flick, the therapist was revealed directing his sessions as strongly as a policeman directs traffic at a busy intersection.
In addition to his wife, Dr. Birdwhistell is survived by daughters, Jill Pierce and Nan Birdwhistell; a brother; and four grandchildren.
A service at which colleagues and former students will talk about his work will be held at 1 p.m. Nov. 5 at the Townsend Residential Center at Richard Stockton College of New Jersey.