Reporting from Big Pine, Calif.-- On a recent weekday morning, Tom and Jo Heindel strode to the top of a hill at the edge of town and held hands, savoring the panoramic views below of elk grazing in alfalfa fields, strips of willows along streams and elm trees glistening with the remnants of rain.

Then Tom, 73, and Jo, 71, got down to business.

"A few dozen scaup, 10 eared grebes, 12 Clark's grebes, 20 canvasbacks and a Northern harrier gliding low and fast," Jo said, peering through a spotting scope.

"Got it," said Tom, transcribing the information on a tally sheet spread across the hood of their aging white mini-pickup truck. "It is 8:50 a.m. and 66 degrees, with 2-mile-per-hour winds from the north under clear blue skies."

Theirs is a love story that dates to a spring day in 1953 when Tom, 16, asked Jo, 14, out on their first date -- bird watching in the Santa Monica Mountains.

Thus began the ornithological passion that has carried the Heindels through 55 years of marriage and careers as high school science teachers in the United States, Bolivia, Ecuador and Saudi Arabia.

But the most significant and enduring contribution of the relationship -- one Jo likes to call "a menage a trois, with birds being the third party" -- began in 1972 as a plan to produce a little guide to the birds of the Eastern Sierra.