The giant ears of rabbits serve at least two purposes. First, they function as air conditioners, helping the rabbit to maintain its normal body temperature.
Rabbits easily overheat because they cannot sweat. The ears contain large blood vessels very close to the surface of the skin. When the rabbit’s temperature rises, excess body heat dissipates from those veins, cooling the rabbit.
Secondly, those big ears act as parabolic antennas, rotating in every direction to intercept all the sounds around the rabbit. It is right that an animal like the rabbit that is prey in nature is not left completely defenseless against predators. While a rabbit has few means of protecting itself, its acute hearing gives it a great advantage.