Ground Squirrels are natural vegetarians. Squirrels like to eat nuts of any kind, with their second choice being seeds. The sunflower seeds in your birdfeeder are what tempt them to clean you out of birdseed. Many species will eat fruit and insects, too. When faced with extreme hunger, squirrels will also eat bird eggs and snakes. As humans have encroached on squirrels' natural habitats, squirrels have learned to eat human food, and will usually eat whatever people food they find lying around.
Squirrels prefer acorns over most any wild food. Squirrels can eat their body weight x 2 of acorns in 1 week. Northern Red Oak acorns are the preferred acorns of squirrels but they will eat almost all acorn species.
Squirrels eat all year round. Contrary to popular belief, squirrels do not hibernate. Tree squirrels are active all through the year. The reason you may not see many of them as often in during the winter months is that they remain in their nests in order to conserve body heat. One of the better known traits of certain species of squirrel is the way they gather and store nuts for the winter. Such squirrels are known as scatter-hoarders as they will collect nuts and store them away in a hiding place, generally by burying them. Squirrels are omnivores; in addition to eating various kinds of plant food, (that includes nuts, seeds, fruits, and green vegetation, they can also prey on insects, eggs, smaller mammals, and the like. These foods commonly replace nuts in a number of the tropics.
No. Squirrels' diet is quite varied as there are over 300 different species of squirrels. However, none eat "greens" (which leaves would fall under) to my knowledge.The Grey squirrel, which would be the most commonly referred to in my circles eats mostly fruit, nuts and seeds.
However, many animals can be seen chewing, gnawing, cutting, tasting, etc. Objects for reasons other than to eat them. For instance, many rodents gnaw on things too hard to eat in order to keep their ever-growing rodent teeth "filed" down. Squirrels may also be seen gathering leaves for their nests. Rodent teeth make very good cutting tools, don't you know.
