In the realm of seven animal senses

Ever since humankind created the industrial system, we’ve been finding ways to streamline the task. We started by replicating the five ‘traditional’ human senses to count objects, weigh them, record sounds, check pH and detect gases. Sensing technology in the 20th century reproduced the human sensor array and gave us the power of mass manufacturing. We also took our first steps out of the human realm and investigated the field of biomimicry that gave us echolocation and the ability to ‘see’ outside the visible light spectrum.

All these sensors, along with decades of immense computing strides that led to today’s AI, have been combined to powerful effect: we can predict weather and natural disasters, navigate to extraordinary accuracy using our smartphones, and take photographs in the dark.

Throughout our technological evolution, we’ve often turned to the natural world for inspiration, finding phenomena beyond our own senses. We’ve discovered animals that can detect electromagnetic fields, infrared radiation and carbon dioxide. We’ve marvelled at creatures that see a hundred times more colours than humans, can harness polarised light or transmit infrasound messages around the globe. Some of these animal senses – such as echolocation – have been a fixture of human technology for decades, while others we’re only just beginning to understand.

Here, E&T takes a look at seven of these animal senses.

Evolutionary sunglasses

Although humans have only a marginal sensitivity to polarised light, many animals – fish, insects, birds, crabs – have evolved highly developed polarisation vision to help them solve problems and perform daily tasks. You only have to put on a pair of polarised sunglasses to realise the advantages of being able to penetrate haze, reduce glare or enhance colours. While this might make us more comfortable when driving or playing sports, in the animal kingdom innate polarised light sensitivity has been put to far more practical use.

According to Science, the greater mouse-eared bat “can do something no other mammal is known to do: they detect and use polarised light to calibrate their long-distance navigation”. It also provides an important visual stimulus for many insects that are able to use polarised light to improve their navigation, while cuttlefish have the most acute polarisation vision known in any animal. Marine biology researchers believe that it could be as important to some animals as colour is to us.

Our most frequent encounter with polarised light technology comes in the form of sunglasses and, as any serious photographer will attest, polarisation filters are a vital tool for reducing glare off highly reflective surfaces, as well as adding definition to cloud shapes. This is because it is impossible to replicate light polarisation in post-processing software, which is why physical filters remain as popular in the digital age as they were in the days of film.

Electric sense of achievement

When it comes to electricity, humans didn’t get involved on a scientific level until the 17th century, when William Gilbert studied the lodestone effect of creating static by rubbing amber (the word electricity comes from the Greek ‘elektron’ meaning ‘amber’). After this, some of the greatest names in engineering became involved: Volta, Ampere, Faraday, Kelvin, Hertz, Tesla, Westinghouse.
But we’ve known about electric shocks for five millennia – the Ancient Egyptians were aware of a type of fish that was electrogenic, and they called it ‘the thunderer of the Nile’. What they didn’t know is that most electric fish are also electroreceptive, meaning that they can sense electric fields.

By the late 18th century, Hugh Williamson was reporting on electric eels to the Royal Society, while Luigi Galvani was promoting his discovery of bioelectromagnetics: the study of the interaction between electromagnetic fields and biological entities. We now know that the human body weakly interacts with electromagnetic fields, but we do not share a magnetic sense with other members of the animal kingdom.

Animals with this magnetic sense include arthropods, molluscs and vertebrates including some fish, amphibians, reptiles, birds and mammals. It’s mostly used for navigation and orientation, while there is some evidence that the sense can also help to produce regional maps in animals.

In other words, while some animals have a broader sense of north-south or pole-equator, others can sense small fluctuations to map their positions to a few kilometres.

Infrared-blooded innovation

Most of us will remember from our physics classes that infrared (IR) is a type of electromagnetic radiation with wavelengths longer than those of visible light. As humans, we sense it all the time as heat, mainly because the sun accounts for half of the heating that happens on Earth.

Apart from in exceptional laboratory conditions, humans can’t see infrared radiation, which means that we have needed to invent specialised infrared cameras and telescopes, as well as night-vision goggles. In such devices, infrared energy radiated by an object is converted into an electronic signal that is then used to produce thermal imagery.

And yet there are some animal species that come with inbuilt biological thermoreceptors critical for aspects of daily survival such as hunting and feeding.

IR imaging pit organs in crotaline and boid snakes enable them to locate live food sources by detecting IR radiation emitted by homeothermic (‘warm-blooded’) prey. The same applies to vampire bats. The black fire beetle (Melanophila acuminata) locates forest fires using IR-detecting pit organs so it can lay eggs in recently burned conifers. Blood-sucking bugs (Triatoma infestans) are thought to have thermoreceptors that help them to estimate prey temperature at a distance. Dark-pigmented butterflies avoid sunburn through IR sensing.

Humans have technologically replicated this sense, routinely using IR in industrial applications such as robotics, automation, medicine and aerospace. Thermal imaging systems are also used in home security, guided missiles, rail safety, human body detection and deep-space astronomy.

Superhuman vision

Most humans can see about a million colours. Thankfully, we don’t have different names for each of them, but the reason we’re able to do this is due to our trichromatic vision. The term itself is easy enough: ‘tri’ and ‘chroma’ come from the Greek for ‘three colours’. The biology is more complex. Put simply, humans are trichromats because we have three independent channels for conveying colour information from three different types of cone cells in the eye.

This is the configuration that we share with some other mammals, particularly our more closely related primate cousins. Some animals only have two channels – dogs for instance – while others have won the vision lottery and have four.

Tetrachromacy exists in some birds and fish that can perceive colour on other wavelengths, including ultraviolet. This enhanced vision means they can distinguish 100 million colours, which animal scientists think may give them physiological advantages over other species – but they’re still working on it. Ultraviolet photography provides us with clues by showing us details unavailable to the human eye.

Some humans claim to be tetrachromats and there are artists whose work attempts to reveal what it’s like to see this way. You can even try a variety of online tests on your billion-colour screen to see if you are a tetrachromat, although BBC Science Focus warns that they are unreliable, and you’d need to go down the genetic testing route to make sure.

The lowdown on infrasound

Just as there are animals with senses that can detect light wavelengths outside of the human visible light spectrum, there are creatures that have evolved hearing sensitivity at frequencies above and below what our ears can sense. We’re familiar with the idea of the dog whistle (more correctly, the ultrasonic Galton’s whistle) being barely audible to humans and yet easily detected by canines. But at frequencies below the lower limit of human audibility (20Hz), animals such as whales, elephants, rhinoceroses and tigers use infrasound to communicate over long distances – in the case of whales, hundreds of miles.

Elephants can communicate with other herds by producing infrasound waves transmitted through the ground by stamping their feet. The purpose of such communication is believed to be the coordination of herd movements to allow mating elephants to find each other.
Scientists have also observed animal reactions to infrasonic waves caused by natural disasters, noting that during the 2004 Indian Ocean earthquake and tsunami livestock had fled from areas affected hours before the arrival of the flooding. The US Geological Survey has also suggested that homing pigeons use low-frequency infrasound to navigate.

Humans have a long history of adapting infrasonics into technology, with the phenomenon used in medical applications such as heart mechanics monitoring (specifically ballistocardiography and seismocardiography), while as far back as the Second World War infrasound was used to locate artillery positions. Infrasound is also one of the techniques used to identify nuclear detonations.

Carbon dioxide killer on the loose

Humans don’t come equipped with the senses to detect carbon dioxide. Most of us will be aware of the role the gas has in the greenhouse effect that leads to global warming, but what may not be so well known is that it plays a role in topping the list of the most dangerous animals in Africa. By far the most lethal killer is the mosquito, which carries a number of potentially fatal diseases including yellow fever, dengue fever and malaria, the last of which accounts for at least a million lives in sub-Saharan Africa per year. The reason the mosquito is so effective in targeting humans is that is able to detect the CO2 in the plumes of air we expel from a distance of 10m.

What makes mosquitoes doubly dangerous is their use of multiple ‘clues’ to find us: they are also attracted by skin odour. Since it’s hard for science to stop us producing CO2 – humans produce it as a by-product of cellular metabolism – researchers are currently working on developing chemicals to switch off the mosquito’s CO2 receptor while conducting body odour wind tunnel experiments.
Because of our inability to sense CO2, humans are vulnerable to poisoning, although this is rare due to the widespread availability of low-cost air quality monitor/alarms. Solid carbon dioxide can often be visually detected at heavy metal concerts, where it is frequently used as the stage prop ‘dry ice’.

Echolocation, echolocation, echolocation…

Back in the 18th century an Italian scientist by the name of Lazzaro Spallanzani thought that when bats fly at night they relied on a sense or senses other than sight.

Building on Spallanzani’s work, Swiss naturalist Louis Jurine reached a similar conclusion, while adding that the other sense was hearing. These early investigations into echolocation were, over the centuries, refined by successive scientists whose research arrived at the idea that there were several species that used biological sonar for navigation, foraging and hunting in environments ranging from caves to the ocean. The principle of echolocation is based on sounds emitted by the animal: bat or whale, swiftlet or shrew. The animal can then calculate its position by interpreting the delay between the signal transmission and the return signal reflected off surfaces in the surroundings.

Unlike some human-made sonars, such as those used in submarine navigation and shipwreck location, in which target localisation can be made based on systems of multiple signal beams and receivers, the biological system has only one transmitter and two receivers (the ears). The neural anatomy of the auditory brain circuitry allows the animal to create a picture of where obstacles and prey are located.

There are examples of human echolocation based on neural implants. British engineer Kevin Warwick has experimented with feeding ultrasonic pulses into the brain and has recorded his findings in his paper ‘An attempt to extend human sensory capabilities by means of implant technology’.