Birds rely on an inner compass to guide long migrations

You’ve likely watched a flock of birds heading south in awe and wondered, how do they know which direction to go? And how do they stay on course for thousands of kilometers?  This winter, neuroscientists and ecologists from Doshisha University and Nagoya University conducted a study to answer this curiosity.

Studies have proven that migratory birds have magnetically sensitive proteins in their eyes and the magneto-receptive cells in their brain that allow them to perceive geomagnetic fields of the earth. This helps migratory birds navigate through new terrains, or travel over the ocean without the help of any landmarks. 

To understand how birds know which direction to follow during long-distance flight, Professor Susumu Takahashi hypothesized that the directional and the magnetoreception senses in birds may share a few common neural players.

For the investigation, the team selected the streaked shearwater bird – a seabird that breeds on islands in Japan, Korea, and China and migrates to warmer regions such as Philippines, Indonesia, and northern Australia in the winter. 

“Interestingly, during their first migratory flight, juvenile birds do not follow the easier detours along the coastline taken by their parents. Instead, they fly directly towards the destination through difficult mountain ranges. This suggests that the juvenile birds rely heavily on the orientation of their in-built compass, rather than the environmental cues followed by the adult ones,” said Professor Takahashi.

The researchers used a device that wirelessly records the electrophysiological activity of the brain. First, they housed chicks in light-shielding cages. Then, they used the device to record the electrophysiological activity from the medial pallium region of the brain. Next, they let the baby birds walk freely in a room  in which the sun’s direction was not visible. The birds also were brought to walk around a sea-facing cliff, a far distance from where they were found.

This experiment revealed that head direction (HD) cells act as an internal compass to help the birds navigate during their initial migratory flight.

This was determined as 20 percent of the HD cells in the medial pallium region fired electrical pulses with higher frequency when the birds faced north. And when birds faced other directions, the cells became less active. The birds had a preference for the north, regardless of what study location they were placed in.  This suggests that the location-independent geomagnetic field was used as a cue for head orientation. 

The researchers are hopeful that these findings will open new doors in future studies. “Our findings suggest that the avian internal compass can be utilized to gain insights into the neuronal underpinning of animal migration patterns,” said Professor Takahashi.

The study is published in the journal Science Advances.

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By Katherine Bucko, Earth.com Staff Writer