They may not be on most people’s list of most attractive species, but bats definitely have animal magnetism. Researchers from the Universities of Leeds and Princeton have discovered that bats use a magnetic substance in their body called magnetite as an ‘internal compass’ to help them navigate.
Dr Richard Holland from Leeds' Faculty of Biological Sciences and Professor Martin Wikelski from Princeton University studied the directions in which different groups of Big Brown bats flew after they had been given different magnetic pulses and released 20km north of their home roost. The findings are published in the current issue of PLoS ONE.
Dr Holland was part of the team which, in 2006, discovered that bats used the Earth’s magnetic field to get around, but until now, how bats were able to sense the field was still unknown. Big Brown bats were put through a magnetic pulse 5000 times stronger than the Earth’s magnetic field, but orientated the opposite way(1).
Dr Holland said: “We had three groups of bats. One had undergone the magnetic pulse with a different orientation, and one control group had received no pulse at all. The third group had undergone the pulse, but in the same orientation as the Earth’s magnetic field. By including this group, we could easily see if changes in behaviour were the result of confusion caused by the pulse itself rather the impact of its orientation on the magnetite.”
The control group made their way home as normal, as did those which had undergone the pulse with the same orientation to the Earth’s magnetic field. But of those which had been through the pulse with a different orientation, half went home but half went in the opposite direction.
“This clearly showed that it is the magnetite in their cells which give bats their direction as we were able to change how the bats used it as an internal compass, turning their north into south,” says Dr Holland. “But as only half were affected, it’s likely there is another mechanism as well, which in some bats enabled them to override the impact of the pulse.”
Magnetite is found in the cells of many birds and mammals, including humans, but if we were once able to find our way by an internal compass, it’s a skill we appear to have lost long ago.
The researchers were able to conduct their unique experiment by use of radio transmitters on the bats which were monitored from the ground and from a plane to verify the signals were correct. However, this kind of monitoring is limited to short distances, so the team is now in discussions with NASA and ESA about using satellites to help track smaller migratory birds and mammals.
The satellites currently used by scientists can only track larger sea birds over 300g, although 60 per cent of mammals and 80 per cent of birds are below this size. The technology exists to track this size of target, but no satellite has yet been launched.
Dr Holland believes tracking this size of bird or mammal is of key importance. “Birds and mammals carry and spread diseases, such as rabies or bird flu, and plotting their migration and movement can help us predict this spread. Large movements of birds can act as pests in themselves, but other species are scarce and need conservation support. We were only able to make our discovery through studying bats in the wild. But for many creatures, satellite tracking is the only way to study them in their natural habitat to help tackle these issues.”
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Notes to Editors
(1) The bats were put into a coil (10cm diameter by 10 cm long) which produced a pulse of 0.4 seconds that was 0.1 tesla in strength.
(2) Dr Richard Holland is a Marie Curie Outgoing International Fellow in the Institute of Integrative and Comparative Biology at the University of Leeds’ Faculty of Biological Sciences. His research interests focus on orientation, navigation and spatial memory in animals. He is also interested in the sensory basis and mechanisms of how animals, in particular bats and birds, are able to navigate to a known goal from unfamiliar areas.
(3) The research was funded by Dr Holland’s Marie Curie Fellowship, the National Geographic Society and the National Science Foundation.
(4) The Faculty of Biological Sciences at the University of Leeds is one of the largest in the UK, with over150 academic staff and over 400 postdoctoral fellows and postgraduate students. The Faculty has been awarded research grants totalling some £60M and funders include charities, research councils, the European Union and industry. Each of the major units in the Faculty has the highest Grade 5 rated research according to the last government (HEFCE) Research Assessment Exercise, denoting research of international standing. The Faculty is also consistently within the top three for funding from the government’s research councils, the BBSRC and NERC. www.fbs.leeds.ac.uk
(5) The University of Leeds is one of the largest higher education institutions in the UK with more than 30,000 students from 130 countries. With a total annual income of £422m, Leeds is one of the top ten research universities in the UK, and a member of the Russell Group of research-intensive universities. It was recently placed 80th in the Times Higher Educational Supplement's world universities league table and the University's vision is to secure a place among the world's top 50 by 2015.
(6) campuspr is a public relations company that specialises in promoting university research and knowledge transfer. Working in partnership with the University’s press office, campuspr is contracted by the Faculties of Biological Sciences and Engineering at Leeds to promote the wealth of research projects, grants, new technologies and knowledge transfer activities that these faculties are actively engaged in. For more press releases, see www.campuspr.co.uk
Citation: Holland RA, Kirschvink JL, Doak TG, Wikelski M (2008) Bats Use Magnetite to Detect the Earths Magnetic Field. PLoS ONE 3(2): e1676. doi:10.1371/journal.pone.0001676
PLEASE ADD THE LINK TO THE PUBLISHED ARTICLE IN ONLINE VERSIONS OF YOUR REPORT (URL live from Feb. 27): http://www.plosone.org/doi/pone.0001676
PRESS-ONLY PREVIEW OF THE ARTICLE: http://www.plos.org/press/pone-03-02-holland.pdf
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PLoS ONE