What is Bat Echolocation
Bats echolocate to navigate and forage in the dark. Sound waves are emitted from their mouths or nose. When the sound hits an object it produces echoes, which return to the bat’s ears and creates a picture for the bat of its surroundings. These high-frequency calls are mainly above the range of human hearing.
What is a Bat Detector?
A bat detector can be used to identify bats in the field by converting bats echolocation ultrasound signal into to audible frequencies. There are 17 known breeding bat species in the UK, and thousands more worldwide. Each bat species hunt different prey species using different predatory strategies. Bat species fly differently and have different morphologies which influence the echolocation calls that they make.
Who Invented the First Bat Detector
In the early 20th century, it was George Pierce who invented the first heterodyne detector, but he was not able to identify bat echolocation calls. Donald Griffin (an American Scientist from New York who was studying the behaviour of bats during 1944) was the first scientist to identify echolocation calls and invented the term ‘echolocation’ to describe these calls. However, he would not have been able to do so without Pierce’s research or sonic amplifier. Pierce was already studying the ultrasonic sounds of crickets and birds; researching levels of sound that human hearing cannot detect. The sonic amplifier was the first heterodyne detector with an audio output.
A scientist in the Netherlands had already identified that bats may be using sound as a way to navigate in the dark. However, it was Donald Griffin and a student called Robert Galambos who identified the first echolocation sounds via the use of a heterodyne detector. Pierce’s detector could not measure the duration of the ultrasonic sounds, but it could record repetition rates, and more sensitive microphones were developed later on. The first commercially sold detectors were dispatched in the mid-1960s.
Investigating Bat Echolocation
From 1940 – 1960, very few scientists saw the need to investigate how bats use echolocation, despite their obvious significance and its use in furthering human technology.
From a series of experiments, Griffin identified the frequency-modulated (FM) structure of sound waves and the CF (constant frequency) calls that are emitted by large numbers of bat species. By teaming up with Robert Galambos, they carried out further experiments demonstrating bat sonar, or echolocation. The experiments were designed to test the bats obstacle-avoidance capabilities in various conditions by impairing other senses. Griffin and Pierce also discovered the directionality of bat calls. For example, if the detector was held directly in front of a flying bat, the echolocation call could be picked up consistently in comparison to when the detector was to the side of the bat. They also observed that different species echolocate in different ways. All microbats produce echolocation calls using vocal cords in their voice boxes, or larynges; whereas fruit bat species emit sounds by clicking their tongues. Bats that transmit echolocation through their mouths, oral transmitters (such as the pipistrelle bat) will fly with their mouths open. Nasal transmitters, on the other hand, (such as the horseshoe bat), will fly with their mouths closed. All bats can feed and echolocate at the same time.
These discoveries had a profound impact on the reputation of bats and people began to view them with fascination instead of fear.
The Discovery of the ‘Feeding Buzz’
Griffin also studied the migration habits of bats and visited one colony of Myotis bats regularly. He studied the relationship between insect capture and the reliability of the ‘feeding buzz’ – the odd noise that bats make as they are about to capture their prey and how successful they were at insect capture. He did this by working with Grey Auger who developed night-vision video methods that could film bats and insects at night time.
The Impact of Echolocation on Technology
Griffin’s discovery of echolocation occurred at the beginning of World War II, and their experiments had an important impact on both wartime and post-wartime technologies. It allowed the exponential advancement of sonar systems. The implications of the experiments that Griffin and Galambos carried out, their discovery of bat echolocation, meant it inspired engineering based on the biology of mammals – bio-engineering.
Cetaceans and Bats Echolocation
The discovery that cetaceans (whales, dolphins and porpoises) too use high pitched frequencies to locate their prey similar to bats, despite their good eyesight, made many scientists question how two mammals not closely related to each other could develop such an evolutionary feat.
This ability arose independently of each other and is called convergent evolution. The ability is thought to have been due to the same genetic mutation within both bats and cetaceans.
From studying evolution, scientists have found that the same traits can be developed in the same couple of steps, but in very different animals. Another example of convergent evolution is the evolution of the eye within vertebrates and invertebrates. Bats developed echolocation to allow them to create an image of their surroundings and their prey, due to them being nocturnal. Cetaceans have developed echolocation for the same reasons, except not because they are nocturnal, but due to some species hunting tactics. For example, the bottle-nosed dolphins used sonar to locate fish hiding underneath the seabed.
Commercial Bat Detectors
David Pye created a heterodyne bat detector with a broadband mode and a tunable transistor built within it. It was the first type of bat detector created that was suitable for bioacoustics professionals and naturalists to utilise. An analogue detector was invented by Justin Halls, and it was this detector that paved the way for others like it. A few years later recording bat detectors followed. The recording bat detectors meant, with the rise of computers, the bat echolocation calls could be played back and easily transferred onto a PC to be analysed for more accurate identification.
Today, large manufacturers provide an endless variety of bat detectors – all with different capabilities and mainly for surveying bats in the field.
Ahead of His Time
Griffin believed that animals had an awareness of their surroundings and had conscious minds like humans – a view that was seen as very controversial despite scientists, such as Charles Darwin, suggesting it many years before. Many people believed animals were no more than computers or machines that would perform behaviours for survival and no more. Despite the critics, Griffin explored the topic and published the book called ‘Animal Thinking’ in 1984, and released another book called ‘Animal Minds: Beyond Cognition to Consciousness’ in 1992. He explained in these books that all animals had conscious thinking; such as creative tool-making in crows, to goal-directed behaviour in rodents.
Today we know that the majority of wildlife are just as capable of the same emotions as human beings, in some ways are as emotive and as intelligent as people. Griffin paved the way for this to be accepted worldwide, as well as providing ecologists with one of the most useful tools to conserve bat species worldwide: the bat detector.
Below is a YouTube clip by Bradley Voytek, which is a compilation of videos that Robert Galambos filmed of himself and Donald Griffin studying the echolocation calls of bats:
Author: Ashley Dale
Interested in this article and want to read more, why not try these blog posts:
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Think you may need a bat survey, please contact Acer Ecology on 02920 650 331, or email enquiries@acerecology.co.uk for further information:
Bat Survey Information I Need a Bat Survey When can Surveys be Done
References
- https://www.ias.ac.in/article/fulltext/reso/010/02/0020-0032
- https://link.springer.com/chapter/10.1007/978-1-4684-7254-7_1
- http://www.zoogdiervereniging.nl/sites/default/files/imce/nieuwesite/Zoogdiersoorten/Vleermuizen%20algemeen/downloads/BatEcholocationResearch.pdf
- http://www.bats.org.uk/pages/bat_detectors.html
- https://books.google.co.uk/books?id=KnFZDwAAQBAJ&pg=PA19&lpg=PA19&dq=G.+W.+Pierce+bat+detector&source=bl&ots=36ECk5j2gQ&sig=WxkkTwx95CE3xSQ7wCQGnhz807w&hl=en&sa=X&ved=2ahUKEwiD5tS956veAhVGXMAKHUNYCG0Q6AEwAXoECAgQAQ#v=onepage&q=bat&f=false
- https://en.wikipedia.org/wiki/Donald_Griffin
- http://www.batresearchnews.org/Miller/Griffin.html
- https://www.sciencemag.org/news/2013/09/bats-and-dolphins-evolved-echolocation-same-way
