Bats use echolocation to generate acoustic maps of their surroundings and to capture prey. They also undertake migrations of more than 1,000 km, between their summer and winter ranges, but very little is known about how they navigate over such long distances.
In a Brief Communication in today’s issue of Nature, Richard Holland of Princeton University and his colleagues describe experiments which provide evidence that bats use magnetoreception to navigate during long journeys.
Holland’s team exposed big brown bats (Eptesicus fustus) to rotated magnetic fields. One group of bats was exposed to a field that was oriented 90° clockwise with respect to magnetic north, and the other to a field oriented 90° counterclockwise. In order to determine whether the bats used the Earth’s magnetic field as well as visual cues such as the position of the sun or other stars, they exposed the bats to the rotated fields 45 minutes before and 45 minutes after sunset.
Holland and his colleagues used radio telemetry from a small light aircraft to track the bats after they were released from sites up to 20 km from their home roost. Radio telemetry is a technique used frequently to track the movements of animals. Each bat was fitted with a small portable transmitter that emits radio waves which are picked up by a receiver.
It was found that the path of the bats was deflected according to the orientation of the magnetic fields to which they were exposed. Those exposed to a field oriented 90° clockwise with respect to the Earth’s magentic field travelled in an easterly direction, while those exposed to a 90° counterclockwise went in a westerly direction. Some of the bats corrected their paths after flying for several hours in the wrong direction.
Homing pigeons have long been known to use the geomagnetic field as a compass-orientation cue, but this behaviour has never been observed in bats. There is some evidence that bats possess tiny magnetite (iron oxide) particles, which are found in birds and other organisms that are sensitive to geomagnetism.