If you ever had a dog as a kid, you may have had a dog whistle. Although you couldn’t hear it, your dog could and he’d come running to see what all the fuss was about. This is because a dog has a hearing range of up to 40,000 Hz.
This unique difference is one of many which various animals possess, giving them the evolutionary edge they need to survive.
1 – Magnetic Fields
The loggerhead turtle has a 10 year migration period in which it circles round the Atlantic Ocean. A study took 79 newly born loggerheads and put them in a circular tank. The tank was surrounded by a big electrical coil and the scientists messed around with it, generating magnetic fields to match those of northern Florida, Portugal and other places on the turtles 10 year circuit. The turtles responded and turned in the direction that they would had they been in migration out in the real world. Nobody is quite sure how the turtles do it, but they detect the magnetic field which surrounds the Earth and grows weaker or stronger depending on where you are.
2 – Infrared Cameras or Thermo-Receptors
The Pit Viper is so called because of a deep pit on either side of its head, just between its eyes and nostrils. These pits are sensitive to infrared radiation to help it find and catch smaller prey. Having two pits allows stereo vision, enabling the snake to determine distance and direction, similar to how infrared cameras work. Experiments have shown that in pitch black, and without the sense of smell, the pit viper can strike accurately at moving objects that are less than 0.2°C warmer than the background temperature.
Other animals with this ability, though not as good as the Pit Viper, are rattlesnakes, boas, vampire bats and some butterflies.
3 – Echolocation and Ultrasound
Echolocation is very similar to SONAR (SOund Navigation And Ranging) where a sound is produced, usually an ultrasound (very high frequency) and the time measured for the sound to bounce back or echo is used to calculate how far away objects are from the source. Several animals have this ability, most notably the bat which uses it to navigate in the almost pitch black caves where it lives and to catch insects into the night. Typically bats call out at a frequency of 14,000 Hz to well beyond 100,000 Hz and can be identified by their frequency. Bat detecting machines are used to record the ultrasounds, since they are virutally all outside human hearing range, and databases or libraries of typical calls have been collected so that specialists can identify specific bat species for whatever reasons.
Whales, dolphins, porpoises and orcas use a similar method, emitting a focused beam of high-frequency clicks. The only known mammals (other than below) to use echolocation are shrews and tenrecs (very similar to the shrew) which emit a series of ultrasonic squeaks. Although unlike bats they use it to investigate their habitat rather than finding food.
Human echolocation has also been known to occur in humans, though only ever in blind people. One remarkable case is of Daniel Kish who clicks his tongue and listens to the echo. Although completely blind, he is able to ride a bike and hike in unknown wilderness. He teaches his echolocation method to other blind people.
Ben Underwood, a young, blind boy, discovered echolocation at the age of five. He is able to detect the position, size and composition of objects near him, and sometimes their shape, also by clicking his tongue. As such he is able to run, play basketball, skateboard and rollerblade.
4 – Electrical Fields
Various sharks have small black dots along their head, face and jaw, which looks like they forgot to shave. In fact these black dots are small pores which lead to little jelly filled canals. The jelly is ultra conductive and the voltage at the pore is measured against the voltage within the jelly. This voltage difference gives the shark an extremely sensitive detection to electrical fields in water, more so than any other animal. The bonnethead shark can detect sensitivities as low as 1 nV/cm (1/1,000,000,000 of a volt measured in a centimeter-long ampulla). For comparison that’s similar to the electrical field generated by an AA battery connected to electrodes about 10,000 miles, roughly 5 million times more sensitive than anything a human could detect. Since living creatures produce electrical fields via muscle contractions and movement, the shark can easily find prey with this method, even flounder and other fish who bury themselves under sand. Additionally, wounded prey thrash more and bleed into the water releasing charged electrolytes which creates an electrical field which can be as much as 3 times stronger than uninjured prey, therefor in bloody or dark waters the shark has a clear advantage.
5 – Ultraviolet World
Most insects, some birds and a few reptiles can see into the near Ultraviolet which is a shorter wavelength than the light visible to humans. Bees are reputed to be able to see ultraviolet light very well which helps them find and chose which flowers to collect pollen from. Recently scientists were amazed to discover a whole new world, hidden in plain sight, when they took special ultraviolet photographs of common plants and flowers. This revealed beautiful patterns which are undetectable to the human eye. Likewise many birds and butterflies have patterns on their plumage or wings only observable by ultraviolet.