The study, published in the journal, Science, and led by researchers at Bangor University, the University of Latvia and the University of Oldenburg, in Germany, has revealed unexpected effects of exposure to electromagnetic noise that is an ever-present feature of urban environments.
The team of researchers exposed soprano pipistrelle bats to weak broadband radiofrequency noise (0-300MHz) for about 30 minutes while they were observing the sunset, then tested their flight orientation later in the night. Previous studies have shown that such noise can disrupt animals' ability to sense the magnetic field.
Because soprano pipistrelle bats migrating towards their wintering grounds are known to calibrate environmental cues at sunset for navigation later at night, the researchers predicted that this would disrupt the bats' ability to sense the magnetic field and thus their calibration of their internal compass system, but would only effect bats when exposed during that crucial calibration period.
They found the bats exposed to this noise took off in random directions, unlike untreated bats, which oriented normally in the expected migratory direction. However, much to the surprise of the researchers, further studies indicated that bat’s orientation is disrupted regardless of whether the exposure was during this crucial calibration period or after it, when the sun had set.
Most surprisingly, the disruptive effects of this electromagnetic noise lasted for several hours beyond the exposure period, suggesting a “carryover effect” of the brief exposure. This was not predicted by the known effects of this electromagnetic noise on the magnetic sense, which is expected to end when the noise is no longer present.
Their findings suggest that electromagnetic noise pollution has the potential to have a greater effect on animal behaviour than had previously been assumed. The research thus raises questions about the ecological consequences of electromagnetic noise for wildlife moving through human-dominated landscapes, such as animals that migrate seasonally, even if they do so only briefly.
Richard Holland, Professor in Animal Behaviour at Bangor University said, “This finding was quite surprising. Our intention was to see how the noise would affect the magnetic sensing system of bats, but the results suggest that the impact of this electromagnetic noise is more complicated than that. Although it is known that electromagnetic noise in this range disrupts the magnetic sense, it was not previously assumed to have a significant impact on migrating animals, because it is more prevalent in cities than rural areas. It was assumed that because animals would move rapidly through it, they would not be affected for very long, if at all. However, our findings indicate that even brief exposure can have effects that last beyond the period of exposure, and independently of other cues.”
Will Schneider, Research Fellow in Bangor and co-author of the study said, "The reason for these effects is uncertain. It may be that the effect is on their interpretation of the magnetic field, for example, because the electromagnetic noise makes it look unusual, the bats decide to ignore it. On the other hand, it might be that it introduces some sort of stressor, that makes the bats decide not to migrate that night, which is why they head off randomly, instead of in the migratory direction, like the untreated control bats. Either way, this surprising carryover effect has the potential for significant ecological consequences that were not predicted by our current understanding of the effects of electromagnetic noise. It is also worrying that current exposure standards are designed exclusively to humans, leaving wildlife vulnerable even within the confines of these guidelines.”