Birds possess an ability that scientists call magneto reception. This is the perception of magnetic fields and is used by avian species to determine direction. When the time comes for many birds to migrate, this capacity becomes more important because their lifecycle depends heavily on the annual trip to warmer climates during winter months. However, research studies are discovering that the magnetic orientation of birds is influenced by human electrical equipment or electromagnetic noise such as AM radio signals. This interference may be a large enough hazard to disorient birds in some urban environments.
The studies that support this claim were led by a man named Henrik Mouritsen per the science journal Nature. What he found after placing European robins in wooden huts shielded from the sun and stars was that the birds became disorientated in an urban environment. Multiple double-blind experiments, or tests where those conducting the research were unaware of which birds where exposed to magnetic fields helped verify the results. Moreover, after shielding the huts with aluminum, the electromagnetic interference was reduced and the birds regained their ability to determine direction.
Multi-sensory informational cues
While the Mouritsen results are interesting, they do not explain other navigational phenomenon such as the ability of birds to navigate at the Earth's magnetic equator. Furthermore, at the magnetic equator the fields become flatter, weaker and change direction making them more potentially confusing to birds per the Journal of Experimental Biology. This indicates the possible use of multi-sensory integration. In other words, magnetic sense may not be the only means by which birds can navigate.
“In laboratory tests, garden warblers were disoriented when a horizontal magnetic field was the only available cue (W. Wiltschko, 1974). In nature, however, additional factors may help the birds to master the situation (see Beason, 1992).”
The NIH Center for Macromolecular Modeling and Bioinformatics also claims birds use the position of the sun, light polarization and star signs when determining direction. In such case, the amount by which magnetic sense is reduced by electrical interference and how much birds rely on this one particular facet to navigate is relevant to how effectively they migrate. Furthermore, the capability of some birds to migrate at night seems to suggest the use of light to measure magnetic direction is not an absolute requirement. This notion is also supported by The National Center for Biotechnology Information, which states the capacity of birds to navigate at the Earth's magnetic equator indicates the reliance of more than one perception to overcome competing directional information.
Photo-reception and bimodal perception of magnetic fields
Some scientists think that birds detect the Earth's North-South axis via photo-receptors that induce chemical reactions. If this is true, then the electrical interference would have to override the effects of light on birds' perception. If birds compensate for interference with one sense via use of another, then the disorientation of the birds in Henrik Mouritsen's research may be due to the complete black out effect used to create a controlled environment. Moreover, since the research required elimination of other influences in order to measure the effect of electromagnetic disturbance, it may be fundamentally flawed if the birds use more than one perception of direction simultaneously.
It is important to note that not all birds are the same, and that only around 17 species of birds have been verified to use magneto reception to navigate. Of these, not all of them may have or share multi-sensory integration. According to a lecture published by the University of British Columbia, Cryptochrome, a biological blue-light receptor, allows birds to navigate using light. Birds that use this method for travel are unable to orient themselves for migratory purposes when the right wave lengths of light are unavailable. However, this does not explain away birds that navigate at night.
The Mouritsen research is relevant, and does provide a basis to make the claim electromagnetic interference with birds' sensory abilities is possible. However, the conditions within the wooden shelters and the single species of bird used in the experiments do not replicate the natural environment in which European robins exist. In addition, if the robin populations are relatively consistent in that same city over time, then the radio interference may not be enough to seriously disrupt the birds' ability to orient themselves sufficiently enough to survive.