Many different animals use the Earth’s magnetic field to navigate when migrating. Because of their impressive long-distance migration, birds are probably the animals best known for their feats of navigation, including the use of a magnetic compass. Sea turtles also well known for impressive navigation and migration.

The magnetic field has three components — declination (angle relative to true north), inclination (angle relative to horizontal), and intensity (field strength). The inclination angle points straight down at the North Pole, is horizontal at the equator, and points straight up at the South Pole. All of the magnetic field components vary geographically. Unlike latitude, there is no regular variation in the Earth’s magnetic characteristics with longitude, which means there is no simple relationship between the detected field and the actual longitude. A simple compass only detects horizontal direction.

Despite this, as described in my book Animal Algorithms¹, research found a mechanism in loggerhead sea turtles that allows them to use the magnetic field to calculate longitude, information the turtles use to navigate on their migration journey in the North Atlantic Ocean. Similarly, it was also previously determined that spiny lobsters can detect longitude as well as latitude, and can orient in the proper direction toward home from a distance of 23 miles. Being able to detect multiple components of the magnetic field, specifically the intensity and inclination, enables animals to form a bicoordinate map. The use of this map sense provides much more accurate navigation capability than is available with just a simple compass.

Magnetic Compass Memory

A recent paper published in the journal Nature examined several aspects related to how sea turtles use the magnetic field. One was their ability to remember specific geomagnetic locations. The other was to attempt to determine which magnetoreception system that sea turtles employ. Regarding the first aspect, one conclusion from the research is that, “The results provide strong evidence that loggerhead turtles (Caretta caretta) can learn the magnetic signatures of specific geographical areas. Such an ability has, to our knowledge, never before been demonstrated in any animal.”² The paper explains the findings in more detail, “Our results demonstrate that turtles can remember the magnetic signature of an area over time spans relevant to their migration patterns; turtles continued to recognize the magnetic field in which they had been fed 4 months after the conditioning period, despite having no additional exposure to the learned magnetic field. Results also demonstrate that turtles can learn the magnetic signatures associated with more than one location.” The practical implication of the results could explain how sea turtles can accurately return to their nesting beaches and foraging regions, even after long time periods. Sea turtles can go several years between visits to their home nesting beaches.

Magnetoreception Mechanism

Despite a significant amount of research and discoveries about the use of the magnetic field by animals, as stated in the Nature paper, “The biophysical mechanism or mechanisms underlying the magnetic map and compass senses have not been determined unequivocally in any animal.” Previous research has shown that determination of specific magnetic signatures requires the detection of both inclination and intensity. Several different mechanisms of magnetoreception have been proposed. One of the mechanisms is the so-called “radical pair theory” that light induces the formation of radical pairs, and that the spin state of these electrons is influenced by the magnetic field. This is a chemical process, with the leading hypothesis involving cryptochrome, a photoreceptive protein.

The research documented in the Nature paper included an experiment to determine if radio frequency fields affect turtle’s magnetoreception. If that is the case, it would provide confirmation that detection is based on the radical pair mechanism. The results showed that the map sense was not affected by radio frequency fields, but that the magnetic compass is affected. The results appear to indicate that the magnetic map sense of sea turtles does not rely on chemical magnetoreception. The authors of the paper observe that the results indicate that, “Two different mechanisms of magnetoreception probably exist in sea turtles; a mechanism underlying the compass sense that is disrupted by radiofrequency fields, and a mechanism underlying the map sense that is not.”³

The obvious question is: Why would an animal have two different mechanisms of magnetoreception? The paper’s authors speculate that the turtle migration pattern is achieved, “In part by using their magnetic map sense to identify magnetic signatures encountered along the route and then using their magnetic compass sense to swim in appropriate directions to help them progress along the migratory route.”

Indicating Intelligent Design

The authors speculate on the origin of two different methods of magnetoreception, “In principle, dual mechanisms might arise if the optimal way to detect direction differs from the best way to detect magnetic parameters associated with positional information, resulting in two magnetic senses, each optimized for different tasks.” Of course, just because it makes logical sense from the standpoint of optimal biological design, it does not mean it will occur through the Darwinian process of random variation and natural selection. In addition, there is a significant difference between a relatively simple directional compass and a true map sense. The latter requires several elements: detection of multiple components of the magnetic field; construction of a map; conversion of the magnetic field measurements to map coordinates; storing coordinates of locations in memory; and, relating a destination goal to the map coordinates. All of these elements exhibit specified complexity that is indicative of intelligent design.

Notes

1. Eric Cassell, Animal Algorithms (Discovery Institute Press: Seattle, 2021).
2. Goforth, et al., “Learned magnetic map cues and two mechanisms of magnetoreception in turtles,” Nature, Vol. 638, 8052 27 February 2025, 1015-1022.
3. Goforth, et al., “Learned magnetic map cues and two mechanisms of magnetoreception in turtles.”