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Migratory bats use Earth’s magnetic field as a compass

Migratory bats can detect and use the Earth’s magnetic field for orientation during their long journeys, according to new research led by Dr. Oliver Lindecke at the University of Oldenburg.

“The Earth’s magnetic field is used as a navigational cue by many animals. For mammals, however, there are few data to show that navigation ability relies on sensing the natural magnetic field,” wrote the study authors. 

“In night-time migrating bats, experiments demonstrating a role for the solar azimuth at sunset in the calibration of the orientation system suggest that the magnetic field is a candidate for their compass.”

Mysterious journey

The study was focused on the magnetic sense of the soprano pipistrelle, a species known for its extensive nocturnal migrations across Europe.

Despite weighing just a few grams, the soprano pipistrelle travels thousands of kilometers each year from northeastern to southwestern Europe. 

The bats navigate the dark skies with astonishing accuracy and, until now, the exact mechanism behind their long-distance navigation remained a mystery.

Secrets of bat migration

Dr. Lindecke, who has dedicated ten years to studying the soprano pipistrelle, points out that there has been limited research into the magnetoreception of migrating mammals, especially in comparison to birds. 

The Oldenburg team’s experiments, particularly along the Latvian coast, have been instrumental in uncovering the bats’ use of the Earth’s magnetic field.

Unique experiments 

At the University of Latvia’s Ornithological Station in Pape, Dr. Lindecke’s team observed tens of thousands of bats migrating along the Baltic Sea coast. They found that these bats recalibrate their internal orientation system at sunset, using the sunset point as a reference for their nocturnal flight paths.

In a novel experiment, 65 soprano pipistrelles were captured and exposed to different magnetic field conditions using a Helmholtz coil. 

The first group experienced a 120-degree clockwise rotation of the horizontal magnetic component, the second group faced both a horizontal shift and a reversal of the magnetic field’s inclination, and a third control group was exposed to the natural geomagnetic field.

Surprising findings

When released in a field lab, the control group bats exhibited a roughly equal split between southward and northward take-off directions. However, those exposed to manipulated magnetic fields showed distinct behaviors. 

The group with only a horizontal shift predominantly flew north-west, while the group with both shifts showed no preferred take-off direction.

Study implications

These results demonstrate one thing in particular, said Dr. Lindecke. “The bats are sensitive to both the magnetic field’s horizontal component, known as polarity, as well as its inclination at sunset – and this still influences their take-off behavior several hours later.”

While the exact mechanisms of the bats’ magnetic compass remain unknown, this study establishes a crucial similarity with birds in their navigation methods.

Dr. Lindecke’s research not only unravels a piece of the complex puzzle of bat migration but also opens new avenues for understanding mammalian navigation. 

The study is published in the journal Biology Letters.

image Credit: Christian Giese

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