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) hits of 2010". In December 2010, in honor of the one-year anniversary of the release of "Angry Birds", Rovio Mobile announced that the game had been downloaded 50 million times, with more than 12 million on iOS devices and 10 million on Android. By January 2014, the "Angry Birds" series had reached 2 billion downloads, including "Angry Birds", "Angry Birds Seasons", "Angry Birds Rio", "Angry Birds Space", "Angry Birds Star Wars I & II" and "Angry Birds Go!" On Christmas Day 2011 alone, 6.5 million copies of the various "Angry Birds" games were downloaded across all supported platforms. In the