The accuracy with which migrating birds head for, and find, their chosen destination has been a source of wonder for many. Research has revealed many interesting facts over the years and many theories abound, but there is still an element of mystery that keeps scientists motivated to find an explanation.

For many years scientists have believed that migrating birds have an internal compass to navigate between their wintering grounds and their nesting areas, which are very often thousands of kilometers apart. Much as a compass that humans use, this internal compass was thought to be strongly influenced by the earth’s magnetic field, but it was not understood which part of a bird’s brain or sensory system was used.

More recent research suggests that a migratory bird’s eyes contain molecules which sense Earth’s magnetic field. These molecules are linked to the area of the bird’s brain that processes visual information. So, the possibility exists that bird species may actually be able to see the Earth’s magnetic field. Research involved injecting migratory garden warblers with a special dye, which can be traced along nerve fibers. The research team injected tracer dye into the bird’s eyes and also into a region of the brain, which is most active when birds orient themselves, known as Cluster N. When the subjects of the experiment got their bearings, both these tracer dyes traveled to the thalamus, which is a region in the middle of the brain responsible for vision, proving that there is a direct link between Cluster N and the eye. Results of this research strongly support the theory that migratory birds use vision of the magnetic field to navigate.

Scientists, not involved in this particular study, have cautioned that these new findings are the not the final pieces of the puzzle of navigation over long distances. A compass can tell you in which direction north, south, east and west are, but that is of no use if you don’t know where you are, therefore a map is also necessary. One researcher has suggested that birds may have magnetic crystals in the bills which sense the intensity of the magnetic field, thereby establishing their physical location.

Certainly scientists are a few steps closer to unraveling the mystery of what guides birds during migration. Nevertheless, the mystery is not solved yet.

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