Bats guided by magnetic compass

Bats use a magnetic compass to navigate over long distances and locate their home roosts, according to a groundbreaking report by University biologists that opens new avenues for research into how animals keep their bearings.

The study, published in the Dec. 7 issue of Nature magazine, has generated international news for helping to solve the long standing mystery of how bats travel long distances.

The international team was led by Richard Holland, a visiting research fellow at the University's Department of Ecology and Evolutionary Biology (EEB).

Historically, it has been difficult to determine the methods bats use to navigate because researchers cannot conduct tests in the laboratory, and existing tracking technology is prohibitively large for experiments in the wild, Holland explained.

The researchers in this case employed novel means to get around this problem, including the use of a small airplane, which was flown by EEB professor Martin Wikelski.

"The majority of small animals, like bats, are very difficult to study in the wild, and our group is starting to push the boundary of what is currently possible by showing that, in fact, we can study animal movement out of the laboratory," Holland said.

To test the hypothesis that bats rely on the earth's magnetic field for navigation, the scientists removed several big brown bats, "Eptesicus fuscus," from their home roost at the University's field station, exposed them to a magnetic field different from the Earth's, and, using radio telemetry for tracking, recorded the direction in which the bats flew once released. A magnetically unaffected bat served as an experimental control during each release.

The bats subjected to a manipulated magnetic field were initially "significantly oriented" in a direction coinciding with the altered field, though some managed to correct the faulty bearing and successfully return to the roost on the night of release.

The latter cases suggest that bats might be able to use external cues to reorient themselves, or that they have still-unknown mechanisms for navigation apart from their magnetic compass, Holland explained.

The success of this experiment opens the doors for other, more expansive avenues of study in the field of animal navigation. Wikelski is currently affiliated with a national consortium of scientists — the International Cooperation for Animal Research Using Space (ICARUS) — which plans to track small animals with comparable radio transmissions, emitted this time from a satellite in space instead of an airplane.

"Soon, if we can get a satellite up, we may even be able to track animals globally — not just bats, but also birds and even insects," Holland said. "Finally, we're getting at long-unanswered questions about how animals travel in the wild."