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Antlers of male deer are used both for display-signaling their gender and dominance-and for fighting other males. Visual communication is used to some extent by nearly all animals, although those with limited vision-for example, cave-dwelling bats-do not depend primarily on this sense. Visual signals have some limitations, as they generally require light and an unimpeded view to be seen. An exception is the display of fireflies, who generate their own pulsating light to attract mates in the darkness.

Sound signals are communicated by vibrational waves produced by one animal, or group of animals, and received by others. Unlike visual signals, sound signals travel easily through darkness, dense vegetation, fog, and even water. Sound signals can also travel significantly farther than visual ones. Elephants often make low-frequency rumblings that resonate over long distances and can be heard by other elephants up to 3 km away. In addition to the complex vocalizations of primates, including humans, sound signals are used most notably by birds, insects, and marine mammals. One bird, the African honey guide, produces loud calls to persuade nearby humans to follow it to bee trees containing beeswax, its favorite food. Once the humans have gathered the honey, the honey guide can easily reach the remaining wax. Insects generally communicate with sound by stridulation, . This way of making sound does not allow for a wide range of pitch, so insects vary their messages by changing the rate or intensity of their sounds. A male cricket will typically quicken his chirps-produced by rubbing his forelegs together-to warn off a competitor and speed up the chirps even more when courting a female. Insects have very limited hearing; so rather than listening, they use vibration sensors on their antennae to receive incoming sounds. Sound signals often travel faster and farther underwater than on land. Marine mammals such as humpback whales broadcast rich vocalizations that can be detected hundreds of miles away. Scientists believe these whale songs serve a territorial or mating purpose. The bottle-nosed dolphin is the champion of creative sound signals, producing a wide spectrum of noises described as moans, squeaks, whines, barks, raspings, chirps, and grunts. The dolphin makes these varied sounds by blowing air through the nasal passage and the blowhole and maneuvering the tonguelike structures located in both passages.