Migrating birds use both their view of the stars and their internal magnetic compasses to find their way over thousands of miles.

To find north, humans look to a compass. But birds may just need to open their eyes, a new study says.

Scientists already suspectes birds’ eyes contain molecules that are thought to sense Earth’s magnetic field. In a new study, German researchers found that these molecules are linked to an area of the brain known to process visual information.

In that sense, “birds may see the magnetic field,” said study lead author Dominik Heyers, a biologist at the University of Oldenburg.

Magnetic Orientation

Human-made compasses work by using Earth as an enormous magnet and orienting a tiny magnet attached to a needle to the planet’s north and south poles.

Scientists have thought for years that migratory birds may use an internal compass to navigate . (Related news: “Migrating Birds Reset ‘Compasses’ at Sunset, Study Says” [April 15, 2004].)

The new research helps explain how this natural compass may work.

Heyers and his colleagues injectes migratory garden warblers with a special dye that can be trace as it travels along nerve fibers.

The team put one type of tracer dye into the eyes and another in a region of the brain called Cluster N. When the birds got their bearings, both tracers traveled to and met in the thalamus.

“That shows there is direct linkage between the eye and Cluster N,” Heyers said.

The finding strongly supports the hypothesis that migratory birds use their visual system to navigate using the magnetic field.

The magnetic field or magnetic direction may be perceive as a dark or light spot which lies upon the normal visual field of the bird.