Animals and Infrasound: A Comprehensive Guide for Physics Students

Summary

Infrasound, the low-frequency sound waves below the human audible range, plays a crucial role in the communication, navigation, and environmental detection of various animal species. This comprehensive guide delves into the measurable and quantifiable data on the physics, theoretical explanations, and technical specifications of animals and infrasound, providing a valuable resource for physics students.

Frequency Range and Wavelengths of Infrasound

Infrasound frequencies range from 0.001 Hz to 20 Hz, corresponding to wavelengths from 300 km to 17 m. The relationship between the wavelength (λ), speed of sound (c), and frequency (f) is given by the formula:

λ = c/f

For example, at a temperature of 20°C, the speed of sound in air is approximately 343 m/s. Therefore, an infrasound wave with a frequency of 1 Hz would have a wavelength of:

λ = 343 m/s / 1 Hz = 343 m

Animal Species Utilizing Infrasound

Elephants

Elephants are known to use infrasound to communicate over long distances, with frequencies ranging from 5 Hz to 35 Hz. The low-frequency vocalizations of elephants can travel for several kilometers, allowing them to coordinate herd movements and maintain social cohesion.

Theoretical Explanation:
Elephants’ large body size and the unique anatomy of their vocal tract, which includes a long, flexible trunk, allow them to produce and detect these low-frequency sounds. The large wavelengths of infrasound can effectively propagate through dense vegetation and over long distances, making it an efficient mode of communication for these large mammals.

Numerical Example:
An elephant produces an infrasound vocalization with a frequency of 15 Hz. Assuming the speed of sound in the environment is 340 m/s, the wavelength of this infrasound can be calculated as:

λ = c/f
λ = 340 m/s / 15 Hz
λ = 22.67 m

This long wavelength enables the infrasound to travel over large distances without significant attenuation, allowing elephants to communicate across their vast habitats.

Whales

Whales, like dolphins, use infrasound to navigate the oceans. Blue whales, for instance, produce infrasound pulses with a fundamental frequency of around 15 Hz to 20 Hz.

Theoretical Explanation:
The low-frequency infrasound produced by whales can travel long distances in the marine environment, where sound propagation is more efficient than in the atmosphere. Whales can detect and interpret these low-frequency signals, which provide them with information about their surroundings, prey, and potential predators, aiding in their navigation and survival.

Numerical Example:
A blue whale produces an infrasound pulse with a fundamental frequency of 18 Hz. Assuming the speed of sound in seawater is approximately 1500 m/s, the wavelength of this infrasound can be calculated as:

λ = c/f
λ = 1500 m/s / 18 Hz
λ = 83.33 m

The long wavelength of this infrasound allows it to propagate efficiently through the marine environment, enabling whales to communicate and navigate over vast distances.

Albatrosses

Albatrosses may use infrasound as a cue for long-distance movement and foraging decisions, particularly in response to microbaroms generated by standing ocean waves.

Theoretical Explanation:
Microbaroms are low-frequency atmospheric pressure fluctuations caused by the interaction of ocean waves, which can generate infrasound in the 0.1 Hz to 0.5 Hz range. Albatrosses, with their keen senses and adaptations for long-distance flight, may be able to detect and respond to these infrasonic cues, using them to guide their movements and foraging activities.

Numerical Example:
Suppose a microbarom has a frequency of 0.3 Hz. Assuming the speed of sound in the atmosphere is 343 m/s, the wavelength of this infrasound can be calculated as:

λ = c/f
λ = 343 m/s / 0.3 Hz
λ = 1143.33 m

The long wavelength of this infrasound allows it to propagate over vast distances, potentially providing albatrosses with valuable information about their environment and the availability of resources.

Tigers

Tigers have infrasonic frequencies buried in their vocalizations, which can be used to verify the hypothesis that sasquatches (also known as Bigfoot) employ infrasound.

Theoretical Explanation:
The low-frequency components of tiger vocalizations, such as roars and growls, can extend into the infrasonic range, typically below 20 Hz. These infrasonic frequencies may serve various purposes, such as communication, territorial marking, and intimidation of rivals or prey. The presence of infrasound in tiger vocalizations lends support to the idea that other large, elusive mammals, like the hypothetical sasquatch, could also utilize infrasound for similar functions.

Numerical Example:
A tiger produces a low-frequency roar with a fundamental frequency of 12 Hz. Assuming the speed of sound in the tiger’s environment is 340 m/s, the wavelength of this infrasound can be calculated as:

λ = c/f
λ = 340 m/s / 12 Hz
λ = 28.33 m

The long wavelength of this infrasound allows it to travel through dense vegetation and over large distances, potentially enabling tigers to communicate and interact with conspecifics across their territories.

Recording Infrasound

Recording infrasound requires specialized equipment, such as Earthworks Precision Audio microphones, which can reach down into the range of 3 Hz and are omnidirectional. DAT recorders are suitable for field recording, while analog cassette and reel-to-reel recorders can also be used, albeit with some limitations.

When recording infrasound, it is crucial to avoid using any filtering, noise reduction, or compression and to verify that the recorder can handle infrasonic frequencies. This ensures that the recorded data accurately captures the low-frequency sound waves produced by animals and other natural phenomena.

Infrasound and Human Perception

Although humans cannot hear infrasound directly, it can still impact human perception and health. For example, infrasound can induce hemodynamic, ultrastructural, and molecular changes in the rat myocardium and may improve cognitive function in humans, as demonstrated in an fMRI study.

However, excessive exposure to ultrasound in air has been suggested to negatively affect human health, particularly in individuals with certain sensitivities or pre-existing conditions. This highlights the importance of understanding the effects of infrasound on human physiology and the potential implications for human well-being.

Conclusion

This comprehensive guide on animals and infrasound provides physics students with a wealth of measurable and quantifiable data, covering the frequency range, wavelengths, animal species utilizing infrasound, recording techniques, and the impact of infrasound on human perception. By delving into the technical details and theoretical explanations, this guide equips students with a deeper understanding of the physics behind the fascinating world of animal infrasound communication and its broader implications.

References

1. Infrasound – an overview | ScienceDirect Topics
2. A Case for Infrasound – CliffBarackman.com
3. Albatross movement suggests sensitivity to infrasound cues at sea
4. Ultrasound and infrasound | Sound: A Very Short Introduction
5. Pei, Z., Sang, H., Li, R., Xiao, P., He, J., Zhuang, Z., Zhu, M., Chen, J. & Ma, H. (2007). Infrasound-induced hemodynamics, ultrastructure, and molecular changes in the rat myocardium. Environmental Toxicology, Wiley Subscription Services, Inc., A Wiley Company, 22, 169-175.
6. Weichenberger, M., Kühler, R., Bauer, M., Hensel, J., Brühl, R., Ihlenfeld, A., Ittermann, B., Gallinat, J., Koch, C., Sander, T. & Kühn, S. (2015). Brief bursts of infrasound may improve cognitive function–An fMRI study. Hearing research, Elsevier, 328, 87-93.