Angry Birds (video game) crates and rocks are incorporated into the structures, and power-ups may be used to enhance the birds to attack hard-to-reach pigs. Also in the levels, players can unlock bonus levels by collecting golden eggs. There are several different types of birds used in the game, distinguished by their color and shape. In the earliest levels only the basic red bird is available. As the player advances through the game additional types of birds become available. Some birds are effective against particular materials, and some have special abilities that may be activated by the player while the bird is airborne. For
Angry Birds (video game) spot on the US App Store a few weeks later, where it remained until October 2010. Since release, the free, limited version of "Angry Birds" has been downloaded more than 11 million times for Apple's iOS, and the full-featured paid version has been downloaded nearly 7 million times as of September 2010. The Android version of the game was downloaded more than 1 million times within the first 24 hours of release, even though the site crashed at one point due to the load, and over 2 million downloads in its first weekend. Rovio receives approximately US$1 million per month