5.2 Acoustic communication

Acoustic communication is a vital aspect of animal behavior, enabling species to convey information through sound. From vocal cords to stridulation, animals have evolved diverse mechanisms to produce and perceive acoustic signals for various purposes.

Sound properties like frequency, amplitude, and duration shape how animals communicate. These signals serve crucial functions in mate attraction, territorial defense, and group coordination, influenced by environmental factors and evolutionary pressures.

Types of acoustic communication

Vocal communication

Non-vocal acoustic signals

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Top images from around the web for Non-vocal acoustic signals

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  Hissing of geese: caller identity encoded in a non-vocal acoustic signal [PeerJ] View original

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Mechanisms of sound production

Vocal cords and syrinx

• Vocal cords are two folds of tissue in the larynx that vibrate to produce sound in mammals
• Air passing through the vocal cords causes them to vibrate, generating sound waves
• The syrinx is the vocal organ in birds, located at the junction of the trachea and bronchi
• Syrinx consists of membranes and muscles that vibrate to produce a wide range of sounds
• Birds can control the frequency and amplitude of their vocalizations by adjusting the tension and position of the syringeal membranes
• Some birds have a two-part syrinx, allowing them to produce two different sounds simultaneously

Stridulation and percussion

• Stridulation is a method of sound production by rubbing body parts together, commonly used by insects and some vertebrates
• Crickets and grasshoppers stridulate by rubbing their wings together, with one wing bearing a file-like structure and the other a scraper
• The file and scraper mechanism creates vibrations that are amplified by the wings, producing the characteristic chirping sound
• Percussion involves striking or tapping body parts against a substrate or other body parts to create sound
• Woodpeckers drum on trees with their beaks to establish territories and attract mates
• Some insects, like the death-watch beetle, create tapping sounds by striking their heads against wood

Properties of acoustic signals

Frequency and pitch

• Frequency refers to the number of sound wave cycles per second, measured in Hertz (Hz)
• Pitch is the subjective perception of frequency, with higher frequencies perceived as higher pitches
• Different animal species produce and perceive sounds across a wide range of frequencies
• Elephants and baleen whales communicate using low-frequency infrasound (below 20 Hz), which can travel long distances
• Many insects and some bats use high-frequency ultrasound (above 20 kHz) for communication and echolocation
• The fundamental frequency of a sound determines its pitch, while harmonics contribute to the timbre or quality of the sound

Amplitude and loudness

• Amplitude is the maximum displacement of a sound wave from its resting position, determining the energy or intensity of the sound
• Loudness is the subjective perception of sound intensity, influenced by both amplitude and frequency
• Sound intensity decreases with distance from the source, following the inverse square law
• Animals can adjust the amplitude of their vocalizations to communicate over different distances and in various contexts
• Loud calls, such as those of howler monkeys and lions, serve to advertise territories and intimidate rivals
• Soft, low-amplitude vocalizations, like the purring of cats or the whispers of humans, are used in close-range, intimate communication

Duration and temporal patterns

Functions of acoustic communication

Mate attraction and courtship

Territorial defense and aggression

Alarm calls and predator avoidance

Parent-offspring communication

Group cohesion and coordination

Factors influencing acoustic communication

Habitat and environmental constraints

Morphological adaptations for sound production

Evolutionary pressures and sexual selection

Interspecific vs intraspecific communication

Species-specific acoustic signals

Acoustic niche partitioning

Heterospecific eavesdropping

Ontogeny of acoustic communication

Innate vs learned vocalizations

Vocal learning and development

Cultural transmission of acoustic signals

Neural and hormonal control

Brain regions involved in acoustic communication

Hormonal influences on vocal behavior

Seasonal and circadian rhythms