Some animals that eat peanuts include squirrels, pigs, field mice and rats, although rats are sensitive to the fungi that grows on peanuts. A variety of birds eat peanuts as well, including towhees, grackles, crows, ravens, jays, woodpeckers, northern cardinals and dark-eyed juncos. Other birds that eat peanuts include pyrrhuloxia, tufted titmice, chickadees, nuthatches, wrens and doves.
Large birds, such as ravens, crows and woodpeckers, prefer peanuts that are left inside the shell or just the hearts of the peanuts, while small birds prefer to break the hearts into bite-sized pieces. Whole peanuts are often included in birdseed mixes, and peanut chunks and peanut chips are enjoyed by birds of all sizes.
The size and type of peanuts that are used in bird feeders are determined by the types of birds enthusiasts wish to attract, as well as the type of bird feeder that is being used. A mesh peanut feeder holds whole nuts, but birds must work harder to retrieve the treats. This gives bird-watchers ample opportunity to observe birds as they attempt to feed. Peanut chips are typically placed in hopper feeders, while peanuts in any form work well on tray or platform feeders, which makes the nuts more accessible to squirrels as well.