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) device, and Apple's iPhone and iPod Touch mobile digital devices, Rovio has released versions of "Angry Birds" for additional devices. An iPad-exclusive version, "Angry Birds HD", was released with the iPad mobile digital device in April 2010. In August 2010, "Angry Birds" was made available to the Palm Pre phone running Palm's webOS operating system through its App Catalog online store. Symbian^3 phones received a version of the game in October 2010, which initially includes only the "Poached Eggs" and "Mighty Hoax" episodes. Angry Birds works on Kindle Fire and Kindle Fire HD. In May 2010, Rovio announced plans for