Sunflower seeds should not make up the majority of a chicken's diet, but are a welcome treat. Sunflower seeds and other treats should make up about 25 percent of a chicken's diet.
Depending on the source, advice varies on whether or not to shell the sunflower seeds. Back Yard Chickens suggests feeding sunflower seeds with the shell on or off. Meanwhile, the Bird Hobbyist recommends shelling sunflower seeds before feeding chickens. Observe chickens as they eat sunflower seeds to determine the birds' preference.
Sunflower seeds have benefits for pet chickens. These treats promote egg laying in hens and feather growth, according to Back Yard Chickens.