Scientific Method —

Bats use the sun to orient flights through the dark

Nocturnal bats use cues from the sunset to calibrate their magnetic compasses …

Dracula may not have been able to tolerate sunlight, but some nocturnal bat species may actually rely on the sun for navigation. A study this week in PNAS shows that the greater mouse-eared bat (Myotis myotis) calibrates its internal geomagnetic compass using cues from the setting sun.

At sunset, the researchers exposed bats to a magnetic field rotated 90° east from its normal orientation. The bats, which were displaced from their home range and released in a completely new setting, flew in a direction 77.6° counterclockwise from the actual direction of their roost. Control bats, which had been exposed to a normal geomagnetic field, flew directly toward home.

In the second phase of the study, another experimental group of bats was exposed to a similarly-skewed geomagnetic field, but only after the glow from the setting sun had disappeared. In this treatment, both experimental and control bats flew directly toward their roosts. Taken together, these two experiments show that the timing of the calibration is vital, and the bats must be taking some cue from the setting sun.

Greater mouse-eared bats are nocturnal and generally emerge from their roosts after the sun sinks below the horizon, but before the residual light in the sky disappears. Their nocturnal strategy makes it rather surprising that the sun—rather than the stars, as previously thought—calibrates their navigational systems. The next step in the scientists' research plan: to figure out what aspect of the sunset the bats are using as a cue.

PNAS, 2010. DOI: 10.1073/pnas.0912477107  (About DOIs).

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