Imagine being kidnapped and blindfolded. Then, you're taken hundreds of miles away from your home. Your kidnappers don't know where you are. Luckily, they have given you a compass. How can you return home?This is where homing pigeons, and other migratory animals, often find themselves. Scientists know that the creatures sense the Earth's magnetic field, and that their built-in compass provides them with the information they need.Problem is, a compass reading is not sufficient. You will need to have additional information, such as a map or a bearing in order to find your way back home.Birds and insects can still perform amazing feats of navigation from one end of the planet to another. They must have additional supersense to solve the problem of navigation. One of the greatest problems in biology is to determine what this supersense could be.Navigational SupersenseWe now have a possible answer thanks to the work done by Xin Hao, Zhejian University, China, and his colleagues. They have found a completely new mechanism that could explain how birds navigate. This mechanism also explains why birds can become confused when they are exposed to oscillating magnetic fields at specific frequencies.This new mechanism is inspired by the properties of a rod-like protein found in the retinas pigeons. MagR, a protein that contains iron and sulfur atoms, is called this. Biologists believe that the iron in the protein MagR could be sensitive enough to the Earth's magnetic field to act as a biocompass.Xin and his colleagues claim that the ferric sulfide sulfide clusters enable a more efficient form of navigation. This is due to the fact that the cluster can fluoresce with a spectrum consisting of three colors, a central peak and two fainter side-peaks.Two factors affect the strength and distance between the peaks of fluorescence: the ambient magnetic field and the electric field. The Earth provides the magnetic field, but Xin and co speculate on birds being able to create their own electric field (bioelectric field formation in most animals).This system is tuned to the Earth's magnetic field, wherever the bird is raised. This is a benchmark, and any movement away will cause the fluorescence's diminishing.The bird can however compensate by altering its internal bioelectric field. As it does so, the fluorescence spectrum's peaks are moved further apart. This is what the bird can see, and the farther it goes from home the farther the peaks are.This process opens up new possibilities for navigation. Birds can fly in any direction to get home.This is the supersense that Xin, co. say birds need to use to navigate. They claim that the birds can sense the geomagnetic field in a completely new way to navigate to their destination.This new explanation solves many problems associated with the current theories of magnetoreception. The problem with biocompasses is that they are difficult to sense because the chemical reactions behind them are weak. The fluorescence of ferric sulfuride is strong, and it can be seen in the retina.Another reason is that thermal noise can easily overwhelm the direction biocompasses point. Thermal noise does not affect fluorescence in the same manner.The problem is that a simple compass reading cannot show you the way back. Xin and cos' new method of navigation does exactly that.This theory also explains why birds are disoriented by magnetic fields that oscillate at certain frequencies. This happens when the oscillation frequency corresponds to the frequency that the iron sulfide and atoms of the field precess in it, the so-called Larmor frequency. This happens when the molecules cease to behave in a way that allows for navigation.Xin and co calculated the Larmor frequency based on the original experiment's details to be 1.3199 MHz for ferric sulfide atoms and 2.6398 MHz respectively. These numbers are very close to the observed values at 1.315 MHz, 2.63 MHz, and much closer to the Larmor frequencies of electrons at 1.288 MHz or 2.576 MHz to whom the experimenters initially attributed the phenomenon.Behavioral StudiesThis fascinating work provides a new perspective on bird navigation. This theoretical approach is just the beginning. This solves the problem of navigation. It also shows how birds could use the mechanism. Pigeons have the MagR protein in retinas.It does not prove that birds use this mechanism. This is a more challenging experimental task and will require behavioral studies.Bionavigation is not the only topic that remains unanswered. What other animals also have MagR protein? Is it used by insects? If so, how? For example, Monarch butterflies migrate long distances along the west coast of North America to find the trees they are looking for. They return the next generation to the exact same trees three or four years later. How is this geographical information possible to be passed from one generation on?These questions and many others will continue to be a focus for biologists for a long time. Xin's and Cos's work is a significant step forward. It also offers engineers who have some spare time a way to exploit the mechanism in navigational technology. For example, to give small, flying drones free of charge, which can be used to help them find their way back home.Ref: Compass Free Migratory Navigation: arxiv.org/abs/2106.12903
