January 2010; Loren Sztajer; via Flickr

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.