With notable field marks (the craned necks, the straining eyes) and clear behavioral patterns (creeping through the brush and scanning the sky), they are fairly easy to distinguish from other homo sapiens. The quirkiness and obsessiveness of this subspecies make them an interesting and fairly obvious subject for chronicling, and Mark Obmascik’s new book, “The Big Year,” is one of several recent attempts to tell the stories of this strange tribe.

Obmascik follows the lives of three men as they each attempt to break the single-year record for sighting the most bird species in North America. In birding circles, such attempts are known as “The Big Year.”

These men, most notably a loud-mouthed New Jersey roofer named Sandy Komito, are the furthest thing from nature-lovers, and to a certain extent the birds themselves are incidental. What they’re really playing is a numbers game. They fly all over the country at a moment’s notice searching for rarities, rushing to the Rockies for a glimpse of a ptarmigan or to the Rio Grande for a look at a clay-colored robin.

Moments of actual awe and wonder, versus moments of competitive zeal, are few and far between, and one wishes that Obmascik had gone back in a later draft and added these once he realized just how joyless this enterprise is. Their pleasure seems akin to checking items off a things-to-do list.

They abhor anything that gets in the way of their single goal. When Komito’s charter boat stops to watch a pod of gray whales, he bawls out the boat’s owner, snapping, “Let’s stop the whale nonsense right now.”

But obsessives make interesting characters, and this is a vastly readable book told in lively journalistic prose. We are pulled along, following Komito and his two closest competitors, as they battle their way through the year, worrying endlessly about finding enough birds and about how the other guys are doing. As their numbers rise and the year deepens, their lives attain the simplicity of a quest, like monks with frequent flier miles.

Along the way, Obmascik threads in bits of birding history, particularly the oft-told story of Audubon and the less-told one of Roger Tory Peterson. It was Peterson who accidentally kicked off the whole notion of a “Big Year,” when he mentioned having seen 572 species in 1953.

It’s telling that Peterson dropped that number in a footnote in his book “Wild America,” and it would have been interesting to see Obmascik attempt to contrast Peterson’s love of birding to the fanatical obsession with numbers among this sub-sect of his followers. But instead of analysis, Obmascik favors the literary equivalent of a car chase: It’s a Mad, Mad, Mad, Mad World With Birds.

For the most part, Obmascik is light on his feet, telling his interesting tale with journalistic sureness, but when he strains to be funny, he treads heavily. He can’t resist the big Ba-dum-da one-liner, and he goes out of his way, even breaking his fine overall flow, to crack whoopie-cushion Jokes with a capital J.

One of Komito’s competitors plagued by seasickness is dubbed the “Dukes of Hurl,” and Obmascik notes, “It’s not easy being green.” A man with a poor sense of smell has a “hapless honker,” and someone who needs to urinate is doing the “wiggly gotta-pee jig.”

This is closer to Sinbad or Carrottop than Bryson, and the jokes sometimes have a bumper sticker feel – “Chicks Happen,” or “His plastic went spastic” – that undermines the overall quality of the prose.

An example of that quality comes in a beautiful description of the sea life off the coast of Monterey or in his description of Harlequin Ducks. The book would have benefited from more lingering descriptions like these of the natural world that birders, like it or not, often find themselves in.

It was just this quality that elevated “Birders” (2002), Mark Cocker’s book on birding obsessives, which was a kind of BBC version of “The Big Year.” Obmascik chooses instead to dwell on the antics and adventures of his wacky crew. In doing so, he has managed to produce a very readable field guide to a strange and obsessive flock.

But he also misses some opportunities, and leaves us wondering why these men are collecting birds instead of coins or stamps.

• David Gessner is the author of ‘Return of the Osprey: A Season of Flight and Wonder’ (Algonquin Books).