Their navigational skills are so reliable that homing pigeons have long been used as one of the world's first forms of long distance communication, but exactly how they find their way home has remained a scientific puzzle. Now a team of Swiss and South African scientists think they may have finally solved the mystery, reports Phys.org

Experts have always assumed the birds used some combination of solar and magnetic cues to navigate — and these skills do appear to matter — but they don't account for all of a pigeon's unique homing abilities. Dissatisfied with current theories, researcher Hans-Peter Lipp from the University of Zurich, Switzerland, and Kwazulu-Natal University, South Africa, decided to test another possibility: that the pigeons can detect the gravity field and use it to navigate.

Lipp first caught wind of this alternative idea after an encounter with Valeryi Kanevskyi from the High-Technologies Institute, Ukraine, who was the first to suspect that the birds were tapping into the Earth's gravitational field. 

"Valeryi had formulated a simplistic yet astonishing theory," recalled Lipp. "I realized that he had solved the map problem by one simple assumption: Birds must have a gyroscope in their brain."

The team formulated a study that could isolate gravitational anomalies, and rule out geomagnetic factors, for testing homing pigeons' ability to navigate. Fortunately, a location where gravity was weaker than usual but where no geomagnetic aberrations were at play was known: a massive circular meteorite crater in Ukraine. The team borrowed some homing pigeons from the nearby town of Novoukrainka, Ukraine, where the birds were trained, and over a series of days released them from the middle of the crater. 

Of the 26 birds that were released, only 18 made it home. Of those 18, only seven made the journey with an efficient, beeline route. The rest chose far more bizarre, disoriented routes. Using GPS devices to track the flock's movements, researchers noticed that the place where the birds seemed to deviate was, sure enough, at the point where they crossed the crater's edge, indicating that the change in gravity must have thrown them off. 

The finding opens the door for whole new areas of research into these incredible animals. While this study has shown that the birds do seem to rely on the gravitational field for navigation, the biological mechanism for this process remains a mystery. What cellular mechanisms could be at play that allow the birds to detect the weak gravitational forces that surround them? Where is their internal gyroscope located, and how does it work?

The team is anxious to begin further studies in the hopes of finding answers to these questions.

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