Humans have many approaches to keeping cool on hot summer days, but rabbits use one that we don’t.
When rabbits begin to overheat, they increase blood flow to their ears through vasodilation. The blood passing through their ears releases heat to the surrounding air. The cooled blood travels back into the rabbit’s core where it absorbs more heat and returns to the ears for cooling.
This image was taken on Sunday afternoon when temperatures were reaching the mid thirties with the humidex. Note the highly visible blood vessels in the rabbit's ears.