Why look at birds? For most of us the answer to this question might not rise above: Why not? According to the U.S. Fish and Wildlife Service, nearly 50 million Americans claim to watch birds. Some of us marvel over the carefree majesty of it all, the possibility of infinity one feels merely by looking up at the sky; some of us see birds as harbingers of disease and flying excrement, circling above, taunting our pathetic winglessness; and some of us see birds and think about dinner. But for essayist and novelist Jonathan Rosen, bird-watching is the consummate activity of the thoughtful modern. “The Life of the Skies” (Farrar, Straus and Giroux, 336 pages, $24) is Mr. Rosen’s engrossing account of his indoctrination into the world of hard-core bird-watching and the frenetic associations his encyclopedic mind draws from regarding them.

“The Life of the Skies” is many books in one. The cheerier bits describe Mr. Rosen’s budding infatuation with birds, his drive to seek out nature amidst the man-made clutter of Manhattan. The sight of birds soaring through the sky gives Mr. Rosen pause to consider the eternal questions of science and art, faith and metaphysics, and the mysteries of the natural world. Every check mark in his guidebook reminds Rosen of his “conquering urge,” the urge we all share to possess a piece of the world.

His passion for birds eventually leads him in pursuit of the ivory-billed woodpecker, which has been “flitting in and out of history, in and out of extinction,” for more than a century. We rarely think of the natural world’s comings and goings as “history,” but it is precisely Mr. Rosen’s purposeful blurring of the scientific and the literary that keeps his epiphany-filled story engaging and provocative. “Poetry, it should be said, can be bad for the environment,” he remarks, before telling of the fateful release of 60 European starlings in Central Park in 1890. The reason? The European starling is mentioned, starlings’ acid droppings eroded the masonry of the American Museum of Natural History; they eventually spread throughout the nation, driving the bluebird out of the Northwest and terrorizing farmers to this day. Another fascinating anecdote: The Museum of Natural History currently maintains an armada of flesh-eating beetles to thoroughly “clean” skeletons for display. One wonders if the beetles — confined to their chamber by “double rows of sticky tape” — might one day be deemed deadlier still than poetry.

Elsewhere, Mr. Rosen follows to Jerusalem a 19th-century ornithologist and Bible scholar named Henry Baker Tristram, whose travels echo the author’s own quest for origins, some mythological and some biological. Mr. Rosen vividly recounts the visions of Alfred Russel Wallace, John James Audubon, Walt Whitman, and even Theodore Roosevelt, describing a devout feather fascination that built reputations and careers, inspired artistic greatness, and, in the case of Roosevelt, saved a life. But there is a dark side to Mr. Rosen’s endearingly dorky devotion to the “republic of feathers.” The book’s most personal moments find Mr. Rosen tending to his ailing father and then heading straight to Central Park to lose himself in a skyward glance.”Birds say life life life, but something right alongside them is always whispering death death death,” he writes. There is a chilling symmetry to the sight of birds flying in formation, a mysterious precision to their seasonal migrations. These are qualities we rarely achieve in our lives.

Then there is the human element. On the trail of the possibly extinct woodpecker, Mr. Rosen observes that this bird reminds us of the contradictions inherent in our want of spiritual freedom and need for material progress: This bird reminds us of “our own desire to be free — to shoot and develop and cut down and expand — and the desire to live among free things that can survive only if we are less free.”

The line Mr. Rosen draws is not wholly his own. The subtitle of his book recalls Bill McKibben’s “End of Nature,” and he invokes Edward O. Wilson regularly throughout the book. But while he clearly admires these two eco-ethicists, Mr. Rosen’s own attempts at sliding readers over from the realm of wonder to the arena of direct action can be jarring. “If we don’t shore up the Earth, the sky will be empty,” he warns. While it’s evident that Mr. Rosen is constantly considering the twin impulses of mastery (and thus killing) versus sublime awe (and thus conservation) as he squints through his binoculars, one wonders if the nation’s other 50 million bird watchers will recognize themselves in “The Life of the Skies.”

Mr. Rosen is at his best when he lets his mind race, embracing the wholesale geekiness of birdwatching. “Is there anything more pleasant than looking?” he asks. He is either the most eager or the most erudite bird-watching companion on Earth, always ready with a quote or anecdote to enrich the situation. It is a vital position, to know what it is we regard — and a form of consciousness that marks us as human. We were modern as soon as we discovered that we were not animals, and Mr. Rosen’s book reminds us of this responsibility as “stewards of the Earth.” Looking up and feeling that awful, impossible yearning for flight, we are reminded of the limitations of human progress. If birds, as D.H. Lawrence put it, “reveal the thoughts of the skies,” then it is in a language we will sooner destroy than comprehend.

Mr. Hsu teaches English at Vassar College. He last wrote for these pages on the novelist Susan Choi.