In the initial launch, the birds used their "classic" designs. For example, Red had a grittier expression and the game featured unique Brazilian-themed backgrounds.
The modding community has created several "Sprites Changed" versions that mix and match assets from different eras.
In version 6.0.6, Rovio updated many of the bird and pig sprites to match their appearances from The Angry Birds Movie . Why Were the Sprites Changed? The reasons for these changes varied by era:
Angry Birds Rio : The Complete Guide to Sprite Changes and How to Download Them