Rovio, the developer behind Angry Birds, just turned down a $2.5 billion buyout offer from FarmVille maker Zynga.

Rovio wasn’t interested because it’s growing faster than Zynga right now, Rovio chief marketing officer Peter Vesterbacka said at the IGNITION conference in New York.

Gamers around the world have downloaded Rovio’s Angry Birds game more than 500 million times, but Rovio isn’t stopping there.

Rovio sells toys, shirts, iPad covers and other kinds of Angry Birds merchandise. The company expects to sell 20 million plush Angry Birds toys this Christmas — and it would be selling more, but it can’t produce enough toys.

via Rovio Says Angry Birds Is Growing Faster Than Zynga.