Sorry, but....
This sounds like the lamest premise ever for a movie--except for bird watchers.
Wow, making a comedy about hemorrhoids would be more exciting than this dull ass log line.
You might want to check out the book. It's not perfect, but it's a very human story about excessive competition. There is a nice underdog story as one of the characters basically throws himself into the competition to cope with his recent divorce (I assume Jack Black is playing him) and has to work his way through the year unlike the other two who live off their wealth. The book isn't really about birds, it is about what brought the three to birding, why they need to compete, how they relate to others in the isolationist activity, etc. The underlying themes are pretty universal to film.
Even among birders, there is debate as to the value of a Big Year; the triviality of counting as many birds in a year as you can is recognized by birders too. But really, the actual conquest of many competitions is something really trivial and symbolic (re: any sport ever played. The arguable absurdity of the competition is not overlooked by the author -- he explores it, especially the effect it has on the characters and their relationships. I think this could be a great documentary or drama or a sort of quiet, quirky comedy (think Wes Anderson), but I agree that it's not really laugh out loud subject matter. If this is attempting to be a rollicking riot of a comedy, it probably isn't going to work, but it may surprise you.