One watch succeeded another through the day, though how the rabbits judged the passing of the time is something that civilized human beings have lost the power to feel. Creatures that have neither clocks nor books are alive to all manner of knowledge about time and the weather; and about direction too, as we know from their extraordinary migratory and homing journeys. The changes in the warmth and dampness of the soil, the falling of the sunlight patches, the altering movement of the beans in the light wind, the direction and strength of the air currents along the ground - all these were perceived by the rabbit awake.
Source: Watership Down, Pages: 55.56
Contributed by: chase