Little did he know at the time that he would soon be identifying two love birds in the likes of his daughter, Virginia, and Rahn, who were married in 1954.
The man had gained a son-in-law and a bird watching partner for life.
From the status of religion student and bird watching protege, Rahn, 71, has become the chaplain of Homewood Retirement Centers in Williamsport, Md., and a bird watching veteran in his own right.
"I know all the local birds by call and some migratory birds," Rahn said. "You just learn them like your mother's voice. You hear it so many times you can't forget it."
Though binoculars hang around his neck, a zoom power scope attached to a tripod is continually at the ready and a guidebook on birds is always tucked into one of his vest pockets, Rahn uses his ears before anything else when he goes bird watching.
Just as his father-in-law taught him, Rahn has been taking prospective bird watchers on guided tours at Renfrew Museum and Park every Saturday in April and May starting at 7 a.m. for 17 years.
"When I show somebody a bird that they've never seen before, I've introduced them to a friend," Rahn said, who, when quizzed, can usually relate bird habitats, their feeding habits and other information.
Though he's most familiar with birds native to this area, like the popular House Finch, Rahn can identify several birds from around the Great Lakes region that he learned when he and his wife lived in Michigan after they were first married. Rahn is also familiar with birds native to the East Coast shoreline.
His favorite bird, and one who's name he once used as his personal CB handle, is the Ruddy Duck, marked by a blue bill, white on the sides of the face, with a black head and a brown body.
Once, with his father-in-law along, Rahn drove 300 miles round trip to see a rare Kirtland's Warbler.
"That's the rarest bird I've ever seen," he said.
Besides the annual public tours at Renfrew, Rahn also participates in the area's annual Christmas Bird Count.
"Bird watching is a challenge. There's a certain amount of pride knowing something someone else doesn't know," Rahn said. "There's always friendly competition with other bird watchers and it's also a social outlet. There's a lot to it."