Scientists Say They've Solved Century-Old Pigeons 'Mystery'

A surprising gut feeling may be helping pigeons find their way home. Pigeons are a well-known group of frequent fliers that can traverse hundreds of miles in a single day, and for thousands of years, humans have used them to carry news, personal notes, and military messages. Scientists have long tried to untangle how pigeons travel without getting lost. Some think the birds detect magnetic cues using light-sensitive molecules in their eyes, while others suggest it happens in the beak or inner ear. "The magnetic sense has been this mystery for almost 100 years," Martin Wikelski, of the Max Planck Institute of Animal Behavior in Germany, tells the AP.

Now, in a new study, Wikelski and other researchers draw back the curtain on pigeons' navigational secrets. They searched for magnetic clues in the birds' organs and found a strong signal in an unexpected place: the liver. Specialized immune cells in the pigeon's liver break down red blood cells and store iron. When scientists temporarily stripped pigeons of those immune cells and let them fly, the birds "just couldn't find their way," says Christian Kurts with Germany's University of Bonn. That suggests that iron-rich liver cells may play a role in pigeons' sense of direction.

The birds' magnetic compasses only got scrambled on overcast days, because they also use the sun as a navigational guide. Scientists have previously wondered whether immune cells could be involved in magnetic sensing, but the new study published on Thursday in the journal Science is the first to present a full-fledged theory. The immune cells are located near nerve fibers in the liver, which may be how the pigeons transmit their "magnetic sense" to the brain, says study co-author Clivia Lisowski. The researchers think other birds and animals like mice could operate using a similar magnetic GPS.

But outside experts say more work is needed to verify the pigeons navigate this way, and to firm up how these signals get to the brain. While the researchers found the strongest magnetic signal in the pigeons' livers, such immune cells have also been spotted in other areas, including the beak and spleen. It's also possible this magnetic puzzle doesn't have a single answer, wrote veterinary pathologist Simon Spiro and biologist Hal Drakesmith in an accompanying editorial. The birds could use different techniques to sense magnetic fields depending on the task. "Indeed, it could be prudent to have more than one way of getting home in the dark," they wrote.