Over a large, still body of water, a flock of waterfowl land with ease on the water’s surface. Each bird keeps its gaze pointed in the same direction, never looking around, and miraculously the entire flock lands without a single bump or collision. A team of zoologists from the Czech University of Life Sciences in Prague set out to find out how these birds managed to do this. Over the course of a year they observed tens of thousands of birds from about 4,000 different flocks across 8 different countries. They found that along with being able to land seamlessly as a flock, birds will always land in alignment with the direction of the Earth’s magnetic field.
For this to happen, birds need to be able to detect magnetic fields. This ability is called magnetoception, and has been observed in use by various vertebrate and insects for discerning direction, altitude, or location. Studies have shown that homing pigeons use magnetoception to navigate, and that when a magnet is attached to the bird’s back it cannot properly orient itself and navigate. It has been long hypothesized that other birds have this magnetic sense as well, though the mechanism is still unverified. There are two main hypotheses in regards to how birds are able to sense magnetic fields: they either use a small piece of magnetite embedded in their beak or inner ear, or they use a magnetism-sensitive chemical reaction in their eyes, that allow them to visualize Earth’s magnetic field.
So when a flock of birds approaches a body of water to land on, the birds will choose to land facing either North or South. How they agree upon which direction is still not known, but this fact greatly reduces the chance of collision. It is unknown whether this magnetic sense plays into how they choose and synchronize their angle of descent, but it has been observed that this does occur, and further reduces the chance of collision to nearly zero. Along with being able to locate North with their magnetoception, the sense also works to help birds and other animals maintain a constant heading in a particular direction. Migratory birds use this to help with navigation across large spans of land or water. The uses and mechanism of magnetoception in birds is still largely unknown, but research is currently being done to explain this unexplored sensory faculty.