The 2014 reboot not only gives the King of the Monsters a new origin but a new nemisis-the M.U.T.O. (Massive Unidentified Terrestrial Organism). Like Godzilla, this creature is old and both creatures existed in a time of a younger Earth where they fed off our planet's naturally higher radiation levels. As the radiation levels subsided, they both moved underground.
Unlike [Godzilla](movie:45291), the MUTO is a parasite that is actively drawn to man-made sources of radiation. Dr. Joe Brody (Bryan Cranston) believing that there is more to the creature, discovers it is using a form of echolocation to communicate another MUTO-a female housed in Yucca Mountain Nuclear Waste Depository in Nevada. The MUTO is likely using infrasound, sound below the range of human hearing, which can travel long distances, possibly across continents. This makes it ideal for long-range communication.
The Science of Animal Echolocation
Echolocating animals emit various calls and chirps and listen to the corresponding echoes to locate and identify nearby objects. Bats generate sound via the larynx and emit through the open mouth. As we have seen in "The Science of Godzilla's Roar", the frequencies emitted from the larynx in flow-driven mode is limited by the size of the larynx; the smaller the larynx, the higher the emitted frequency.
Animals determine both distance and direction by measuring the difference in time it takes for the echo to reach the right and left ears. They have also evolved to echolocate using specific frequency ranges to suit their environment and find prey. The frequency used determines the prey they hunt.
Animals find smaller prey by using higher echolocating frequencies. Higher frequencies with their shorter wavelengths mean animals can resolve much finer details and find smaller insect prey, giving them a more accurate picture of their environment. This is the reason why most echolocation takes place in the ultrasonic range.
Ultrasound is not without disadvantages. The sound's amplitude decays very quickly as its energy is absorbed by the air and various objects. This very short range means most animals can only detect prey a few meters away.
This poses a problem for MUTOs who not only need to communicate with each other but find food over long distances, possibly across continents. MUTOs can get around the communication problem by using infrasound; sound below 20 Hz, the lower limit of human hearing.
Both Godzilla and MUTO are large creatures with big larynges and we expect their voices to fall into the infrasonic range. Unlike bats, MUTOs won't be able to use their echolocating abilities to find or resolve very small objects. Hopefully they have good eyesight.
Infrasound Communication and Echoloaction
Infrasound, with its much longer wavelength can travel much further distances than either ultrasound or sound in our hearing range. Infrasound emissions, for example, from the 2013 Chelyabinsk meteor which exploded high over Russia on February 15, was picked up by USArray infrasound stations some 15,000 km (9,321 miles) away; across Alaska and the US North West Coast.
The brain uses subtle differences in sound intensity and timing cues to determine a sound's origin. The human ear distance is about 21.5 cm (8.5 inches), smaller than the half-wavelength for sound at frequencies lower than 800 Hz. The human auditory system can detect differences at these wavelengths without confusion and determine direction.
Below 80 Hz, human ear spacing makes it difficult, if not impossible, to determine direction; the subtle differences we hear are just too small for us to detect. This means that infasound may be a rather poor choice for echolocation unless a Kaiju has an extremely large head. While infrasound communication is possible, it makes infrasound echolocation very unlikely.
Ultrasound and Echolocation
MUTOs are not the only creatures who communicate over long distances. Blue whales use infrasound to hear and communicate with other whale pods across vast distances. These calls can travel distances more than 965.6 km (600 miles). Blue whales also use ultrasound for echolocation and possibly as a means of short-range communication to keep a pod together during migration as well as signal others of danger.
Elephants also hear and emit infrasonic calls. A replica of this signal is sent through the ground as a seismic wave, traveling more than 1.5 times faster than through the air. In this way, elephants can use ground vibrations to communicate and determine where other herds are from far away.
Strictly speaking, what elephants do is not echolocation. The infrasound signal is not bounced off other elephants to return to its sender. Rather other elephants hear the infrasonic rumbling and respond to that communication. The same applies to whales.
While we may know nothing about the complex sensory world of the MUTO or any of the Kaiju for that matter, it is here Dr. Brody gets it wrong. The signals he detects from the MUTO isn't a form of echolocation but rather communication.
This doesn't mean that MUTOs don't echolocate. It is quite possible they can emit ultrasound to find out about their environment at short distances. But for sound to travel across continents, it has to be in the infrasonic range. In this case, the signal doesn't bounce off the female but, rather, she hears it and sends a return message to come find her.
This is good news for the future as it allows humanity a means to track MUTOs. The Comprehensive Nuclear-Test-Ban Treaty Organization maintains a network of infrasound sensors to monitor above ground and aerial nuclear explosions. The network will require little modification to search for and track future MUTO dangers.
Barclay, Robert M. R., and R. Mark Brigham. “Prey Detection, Dietary Niche Breadth, and Body Size in Bats: Why Are Aerial Insectivorous Bats so Small?” The American Naturalist 137.5 (1991): 693–703.
De Groot-Hedlin, Catherine D., and Michael A. H. Hedlin. “Infrasound Detection of the Chelyabinsk Meteor at the USArray.” Earth and Planetary Science Letters ScienceDirect. Web. 2 June 2014.