a flock of multi-colored birds that are attempting to save their eggs from green-colored pigs. In each stage of the gameplay, the pigs are sheltered by structures made of various materials such as wood, glass, and stone resembling children's toy building blocks. The objective of the game is to eliminate all the pigs on the level. Using a slingshot, players launch a limited set of birds with the goal of either striking the enemy pigs directly or damaging their surrounding structures, causing the blocks to collapse and pop the pigs. The player must set the angle and force of the bird's travel by pulling back on the slingshot (using intuitive touch-controls in the mobile versions). The launch process is quick and casual, with no visible trajectory data, and a player simply selects a point in the X-Y field behind the launch post from which the virtual slingshot will be released. In various stages of the game, additional objects such as TNT 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 hidden 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 cardinal whose name is Red 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 example, Chuck, a canary speeds up; Bomb, a loon explodes, hence the name; a bluebird named Jay fragments from his siblings, Jake and Jim; a Leghorn hen called Matilda can drop an explosive egg-shaped projectile; a galah named Stella can trap objects in bubbles; Hal, an emerald toucanet boomerangs back; a giant cardinal named Terence, appears and functions similarly to Red, but deals more damage than his smaller counterpart; and a Jamaican oriole named Bubbles expands and inflates. The pigs also vary, with hardiness relative to their size. Small pigs are weaker and are easily vanquished by direct hits or by debris from the damaged structures, while larger pigs are able to withstand more damage before succumbing to defeat. In addition, some pigs wear hats or armor, making them even more resistant to damage.