My husband, Jeff, is a reasonable man. Calm, clear-thinking, very together. Now and then, however, there are moments when his passion - a rare combination of unshakable focus and uncontrollable energy - completely overtakes him. The most breathtaking of these took place one sunny weekend a few years ago, when, in a most unsuspecting instant, I saw my husband for all the fiery intensity he can be. There were foreshadowings of this phenomenon as early as our first date, which took place one brisk, late-October morning on a birdwatching outing to Reid State Park on the coast of Maine. Jeff and I were poking down seasonally deserted Route 127 in his antiquated Volkswagen Beetle when we came to a bend in the road. We were small-talking about music theory or some other college course we were taking, when in mid-curve an exuberant ''Eeeehawww!'' bellowed from somewhere deep inside my date. I nearly sprang through the roof, not because I feared for my life (though some people might have!), but because this was the same shy trumpet player who had moseyed out of the practice room so many times, face ablush, staring at the coffee-stained carpet, waiting for me to initiate conversation. I didn't question the reason for his little outburst; after many late-night practice room conversations at the college, I had a good idea what his enthusiasm was about. And his face, following his discontainment, was that familiar purple-pink. There was no mistaking that this was indeed the same Jeff. Since that first date, Jeff's spontaneous and uncompromising enthusiasm at odd moments has continued to lead him into risky territory. It's lured him into fields of high brush, where he's disappeared without warning, only to reappear hours later, sticky with burdocks. It's called him through ice-laden streams and out into hopelessly dark nights. But the one moment that epitomizes Jeff's sheer, unbridled passion has become a symbol in my mind of the incomparable joy one can experience once the boundaries of expectation have - if only for an instant - been shattered. That weekend, the two of us, my parents, and my niece had just climbed the monstrous hill to the Hitchcock House on Maine's Monhegan Island, where it had become tradition for us to spend two glorious weekends each year. Famous among birders as a migration stopover and a haven for vagrants, it's commonplace for total strangers disembarking the ''Laura B.'' to ask anyone ashore who's binocular-clad what's been seen on the island over the past few days. That weekend was no exception and included vast numbers of thrushes and orioles, a cerulean warbler, a peregrine falcon - all remarkable but certainly believable. It was with some doubt, however, that Jeff accepted word about a reported Swallow-tailed Kite, a would-be first-time showing of the species in Maine. As we rested in the comfort of our efficiency, Jeff calmly puzzled over the rumor. Until a streak of black and white veered past our window. Jeff was instantly midair, hurdling a table, straddling chairs, dodging backpacks. His voice blasted the walls and rocked through the open door: ''Swallow-tailed Kite!'' Before the rest of us could blink, my love was out on the deck, binoculars to his eyes, smiling a most satisfied smile.