Jackrabbits have REALLY big ears. Their big ears are well-vascularized as you can see in the photo above. These blood vessels dilate (widen) when it is hot outside to help the animals give off heat to their environment by routing warm blood from their core to their ears. Having such an efficient cooling mechanism means they can conserve water by avoiding the need for evaporative cooling (sweating or panting).
As we near the end of summer, I too wish I had big ears.
Categories: Comparative Physiology