How do homing pigeons know where they're going? It turns out that they have a natural advantage. Researchers have found a group of 53 cells within a pigeon's brain that respond to the direction and strength of the Earth's magnetic field. This finding, published in Science, could answer long-held questions about the ways that birds are able to navigate.

David Dickman of the Baylor College of Medicine and his colleagues set up an experiment in which pigeons were held in place while the magnetic field around them varied in strength and direction. They then measured the electrical signals from each of the 53 neurons as the field was changed.

The researchers found that each neuron had its own characteristic response to the magnetic field. In fact, each gave a kind of 3-D compass reading along the familiar north-south directions in addition to pointing directly upward or downward. Each cell also showed sensitivity to field strength, with the maximum sensitivity corresponding to the strength of the Earth's natural field. Theses feature could help the bird not only determine in which direction it was heading, but also be able to reveal a kind of GPS location of its approximate position.

Although researchers had reported in the past that birds do not seem to respond to the polarity of the magnetic field, this new study overthrows the 1972 paper that appeared in Science.

While this study reveals that pigeons can indeed sense the magnetic field, the question of how they actually do it remains a mystery. There are currently several hypotheses in the field. One believes that bird navigation arises in cells that contain tiny chunks of metal in their noses, beaks or an inner ear organ. Another theory states that a magnetic sense may appear in the bird's eyes.

However they do it, it seems that pigeons do indeed have a GPS. That makes flying home a lot simpler.