Compared with birds, the visual ability of beasts is rather poor; some beasts can only distinguish a few colors; while some others are totally colorblind. Nocturnal beasts all have very good night vision. But the senses of smell and hearing of all beasts are quite sharp. They usually communicate with their fellow beasts through sense of smell. Some beasts let off their wastes and urine in fixed places, or smear their gland secretion on tree trunks to disseminate information for the allocation of their territories or for courtship. Crying is also one of the major communication tools among many beasts. Gibbons will whistle loudly every morning; wolves will howl to communicate with peers during the night; whales and dolphins also have special sounds of crying and dolphins can scout the surrounding situations through ultrasound waves too. Bats observe the surrounding situations and catch insects by completely relying on their sense of hearing.
