Melody In Memoriam

I am sitting on the train in seat 10d, which is the window seat. Across the aisle and up three rows, sitting in seat 7a, which is also a window seat, is an elderly man reading a hardcover novel. Since departing, approximately two hours ago, he has been reading this novel with what, to me, appears to be an enviable degree of meticulous contemplation. However, after completing each chapter, (or fragment) he places the book on his lap, turns his head to look at the landscape, and whistles a melody. Initially, of course, everyone was annoyed, including myself. But, after several repetitions of this pattern, it seems the level of irritation amongst my fellow travellers and I has diminished significantly, giving way to an intent admiration towards the melody. Each time he cycles through the sequence, while looking out the window with the book on his lap, everyone gives their undivided attention to every minute detail of the song, as the sequence itself contains a perplexing amount of notes, and each sequence is repeated verbatim, every time. Try as I might, I cannot recognize what piece of music his melody is derived from. Just a moment ago, a Via Rail employee approached him during one of his whistlings, and placed her hand on his shoulder. Abruptly, the man stopped his song, and, establishing an apologetic tone, began to speak, when the employee cut his apology short. The woman told the man that, no in fact, no one was bothered by his whistling, and that, in fact, she and everyone else were quite amazed at how closely his whistling resembled that of a bird. The man gives a quick scan of the train. It's easy to tell he's more than a little embarrassed at the attention. Quietly, he explains to the young woman: 

"I'm so sorry, I didn't mean to bother anyone. My wife just passed away from cancer. It's nothing more than a coping mechanism. I try to read in order to distract myself, but every time her image interferes. So, every time I see her image, I whistle her favourite song, in memoriam." 

With that, the woman fell silent. The man musters a reassuring smile, and returns his gaze to the pines and grassy fields drifting by in the distance. 

Funny, now throughout the car I can hear other attempts at the same melody, hummed awkwardly; patchy variations on the original, perfected theme.