We may have just learned that Angry Birds was coming to Facebook earlier this month, but the developers at Rovio have been working on the game for almost a year.

The reason for the lengthy development time is that the studio is rebuilding the game for the new platform, as opposed to simply porting an experience that might not fit very well.

“You can’t take an experience that works in one environment and one ecosystem and force-feed it onto another,” Rovio’s Peter Vesterbacka told Inside Mobile Apps. “It’s like Zynga. They can’t just take FarmVille and throw it on mobile and see what sticks. The titles that have been successful for them on mobile are the ones they’ve built from the ground up for the platform.”

He also revealed that we can expect a beta for the new game around the middle of next month.