Magnetoception and Changing Geomagnetic Poles

You may have heard the news that the Earth’s magnetic field (also called the geomagnetic field) is changing. (The field itself is created by the molten iron in the Earth’s outer core and other factors.) Specifically, it’s been significantly weakening over the last 200 years (by about 15%), and the geomagnetic North pole has been moving… and its movement is accelerating. The geomagnetic poles may in fact switch, with the North becoming the South and vice versa.

However, such a reversal may not really have a huge impact on life on Earth. This is because this kind of switch is thought to actually happen a lot (speaking in geological times) — it last happened about 800,000 years ago, and we haven’t found any mass extinctions related to the event. But that doesn’t mean that such a change wouldn’t disrupt lives. Read on to find out about some of the many critters that use Earth’s magnetic field to figure out their location and how to navigate to a different location. We have lots to learn about how such animals use this ability, called magnetoception.

• Bacteria: Some bacteria (called magnetotactic bacteria) use Earth’s magnetic field lines to align themselves and move in directions along the lines. It’s thought that the bacteria accomplish this using iron particles in their cells, giving them characteristics of a magnet.
• Mollusks: Some mollusks have been found to be more likely to turn in a certain direction based on the direction of Earth’s magnetic poles. (When the poles were reversed in laboratory tests, no significant preference for turning one of these directions was observed.) But it’s still unclear whether these mollusks are using magnetoception or something else.
• Fruit flies: The genetics and development of fruit flies is well-characterized, but even with these animals it’s unknown exactly how navigation is accomplished using the Earth’s magnetic field. It’s been found that fruit flies can learn to use magnetic fields to get a sweet reward. But some mutant flies, specifically ones that have trouble seeing certain colors, couldn’t be trained. So while fruit fly navigation can utilize magnetic fields, we still don’t understand quite how light plays a role.
• Birds: While homing pigeons clearly use magnetoception, it’s unclear how it’s accomplished exactly. In certain conditions, they rely on Earth’s magnetic field to navigate (such as when it’s overcast), and they can also be somewhat trained to respond to the presence of magnetic fields to get a treat. It’s thought that they may have something like a compass in their beak (made out of iron particles becoming magnetized), and/or use a light-mediated mechanism (similar to the fruit flies). Chickens (and some other birds) may also have a compass-like mechanism in their beaks that allow them to have magnetoception.
• Grazing animals: It’s been shown that at least some grazing animals — certain deer and cattle — appear to align their bodies along the North-South geomagnetic axis, but other factors can affect this alignment (e.g., sunlight, wind, slope, power lines).
• Mammals: Mice, rats, bats, and certain foxes are thought to use magnetic fields to navigate somehow. Specifically, studies done with mice have found that they can likely use the magnetic field to get home (but only if other, easier cues are missing — such visual cues and smells). However, even these studies are inconclusive. Bats are also thought to possibly use magnetoception to navigate over longer stretches (in addition to echolocation for shorter distances). And there’s a great video showing how red foxes (Vulpes vulpes) typically jump in a certain direction to pounce on prey.
• Humans: There have been conflicting reports about how a magnet on a person’s head may affect their directional abilities. Additionally, it’s been found that humans have a light-related protein that’s similar to the one that fruit flies have that’s connected to how the fruit flies can navigate. Many more studies need to be done in humans for us to figure out whether we truly have magnetoception or not.
• Other animals: Many other animals are suspected to use magnetoception, including some fish, newts, turtles, honey bees, and butterflies.

So while Earth’s changing magnetic field may not drastically alter life on the planet, since animals appear to have largely survived the last time the poles switched, it’s still important to consider what could happen to critters that use magnetoception. Many studies have been done to answer this, but investigations into the underlying mechanisms are still very much ongoing.

For further reading:

• Stephen Luntz’s article “Earth’s Electromagnetic Field is Weakening”
• Jonathan Amos’ article “Esa’s satellite Swarm launch to map Earth’s magnetism”
• Patrick Lynch’s article “2012: Magnetic pole reversal happens all the (geologic) time”
• Thorsten Ritz, Salih Adem, and Klaus Schulten’s article “A Model for Photoreceptor-Based Magnetoreception in Birds”
• Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre