In Anglo-Saxon pagan tradition, there was a goddess called Eostre known as the goddess of spring. Her main symbols were the egg and the rabbit. There was a legend that the goddess found an injured bird during winter and in order to save its life, she transformed it into a hare. Although it was no longer a bird, the hare was able to lay eggs.
Actually, the first Easter Bunnies probably were not rabbits at all, but instead hares. It is unclear why this change from hare to rabbit occurred, but one noticeable difference between hares and rabbits is that hares are generally larger. They tend to have longer legs and ears just like the modern day Easter Bunny.