Bird food is food (often varieties of seeds) eaten by birds. Humans generally make or buy bird food to feed to pet birds or use in bird feeders. The choice of what to use as bird food depends on the species of bird being fed.
Bird seeds
Black sunflower seeds are highly recommended for use in bird feeders because they attract a wide variety of birds, have a high ratio of meat to shell, and are high in fat content.Other common birdseeds include niger, or thistle seed, a favorite of goldfinches, millet for sparrows and juncos, and safflower for cardinals, among others.
Non-seed bird food
Not all birds eat seeds. Suet (beef or mutton fat) is recommended for insect-eating birds like nuthatches and woodpeckers. Nectar (essentially sugar water) attracts hummingbirds.
Commercial bird food
A wide variety of commercial bird food is available to bird owners. However, bags of mixed birdseed often combine attractive bird food like sunflower seeds with "filler" materials that birds enjoy less. Birds tend to pick out their favorite seeds and simply leave the rest uneaten. Other birds that favor some of the seeds that were not eaten will then come and eat those seeds