Cows and deer have a fascinating habit of aligning their bodies north-south when they lie down in the grasslands. This behavior has been confirmed through satellite imagery analysis. In 2008, a joint research team from Germany and the Czech Republic statistically demonstrated this tendency by analyzing 8,510 cows from satellite images around the world.
It is believed that these animals possess an internal "biological compass" that allows them to sense the Earth's magnetic field. Currently, two main mechanisms are considered plausible. First, there is a theory that magnetite, a magnetic mineral embedded in their nasal cavities, directly detects geomagnetism. This mechanism is also observed in migratory birds and salmon. Second, another theory suggests that a protein called cryptochrome, found in their retinas, senses the interaction between light and geomagnetism to determine direction.
Interestingly, there have been observations that the orientation of cows and deer is disrupted in areas with strong artificial electromagnetic fields, such as high-voltage power lines. This suggests that external magnetic fields may interfere with the accuracy of their "compass."
The true advantages that this "internal compass" provides to animals are still not fully understood. Researchers are exploring various possibilities, such as whether aligning in the same direction helps them detect predators more quickly, conserves energy by minimizing unnecessary movements during rest, or maintains order by preventing collisions with one another. However, conclusive evidence has yet to be obtained.