Senses and communication
Rats are nocturnal animals and they have rather poor vision. They avoid areas with a light intensity of > 25 lux. Their sense of smell, touch, and hearing is well developed. The animals perceive and are sensitive to ultrasound (>20kHz). Rats communicate with each other by means of pheromones and (ultrasonic) vocalizations. Of the sounds they produce, a frequency of ~20kHz is associated with pain or discomfort (see movie 1), and a frequency of ~50kHz with increased well-being (see movie 2). Specific ultrasonic calls are produced in aggressive and sexual situations and mother/pup interactions.
pheromones play an important role in rat communication. Pheromones are emitted to warn conspecifics of danger, to scent-mark territories, to interact with the opposite sex etc. In rats as in mice, the olfactory organ is the most important sense organ.
Rats also have well-developed whiskers. Bending of whiskers by touching or via movement of air, leads to a nerve impulse that registers in the cerebral cortex.