Thursday, December 07, 2006

 

Home and away: Bat uses magnetic compass for long flights

Scientists believe a species of bat has an inbuilt magnetic compass to find its way home over long distances, in addition to its famous echolocation*, which guides it around its neighbourhood.

Princeton University batologists used radio telemetry aboard a small aircraft to track big brown bats (Eptesicus fuscus - info) that were released 20 kilometers (12 miles) north of their home.

They first tested a 'control' group of bats, which headed due south towards the roost without a problem.

Two other groups of bats were then exposed to a false magnetic field for 90 minutes, comprising 45 minutes before and 45 minutes after sunset.

One field was 90 degrees clockwise and the other was 90 degrees anticlockwise from magnetic north.

The point of this was to see whether the bats used Earth's magnetic field as a guide and, if so, to see whether the bats used sunset or the stars as an additional cue.

The 'clockwise' group of bats flew due east, while the 'anticlockwise' group went due west, suggesting that they had been using a magnetic compass that may have been calibrated by the sunset.

Continued at "Home and away: Bat uses magnetic compass for long flights"
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Based on the journal Nature paper "Navigation: Bat orientation using Earth's magnetic field"

Abstract

Bats famously orientate at night by echolocation, but this works over only a short range, and little is known about how they navigate over longer distances. Here we show that the homing behaviour of Eptesicus fuscus, known as the big brown bat, can be altered by artificially shifting the Earth's magnetic field, indicating that these bats rely on a magnetic compass to return to their home roost. This finding adds to the impressive array of sensory abilities possessed by this animal for navigation in the dark.
doi:10.1038/444702a
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*From the Michigan Museum of Zoology:

Bat Echolocation:
Bats can see as well as humans can, but they have evolved a sophisticated method of using sound that enables them to navigate and find food in the dark called echolocation. Bats produce echolocation by emitting high frequency sound pulses through their mouth or nose and listening to the echo. With this echo, the bat can determine the size, shape and texture of objects in its environment. Bat echolocation is so sophisticated that these animals can detect an object the width of a human hair.

Shouting Bats & Whispering Bats
Bats can be broadly characterized by their echolocation calls as shouting bats and whispering bats. Big brown bats and little brown bats are shouters and produce sounds (if we could hear them) of 110 decibels or similar to the loudness of a smoke alarm. Northern long-eared bats are whispering bats and produce sounds of 60 decibels (similar to the levels of normal human conversation). Shouters tend to forage for food in open spaces; whisperers glean insects from the foliage of trees and forage in the cluttered environments of forest interiors.

Not All Bats Echolocate
About 70% of all bat species worldwide have this ability. Also, bats aren't the only animals that use echolocation. Whales, dolphins, porpoises, oilbirds and several species of shrews, tenrecs, and swiftlets use a similar technique. [More]
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And an open access/free paper from the Proceedings of the National Academy of Sciences (PNAS):

"Integrated fossil and molecular data reconstruct bat echolocation"

Molecular and morphological data have important roles in illuminating evolutionary history. DNA data often yield well resolved phylogenies for living taxa, but are generally unattainable for fossils. A distinct advantage of morphology is that some types of morphological data may be collected for extinct and extant taxa. Fossils provide a unique window on evolutionary history and may preserve combinations of primitive and derived characters that are not found in extant taxa. Given their unique character complexes, fossils are critical in documenting sequences of character transformation over geologic time and may elucidate otherwise ambiguous patterns of evolution that are not revealed by molecular data alone. [Continued at above link]

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