Behavioral testing of animal magnetic sensing in the laboratory and the wild. Typically, measures range from a observing body alignment in inactive or moving animals, e.g. in termites which occupy resting positions perpendicular to the magnetic field direction [6], to manipulations of the animal or its immediate surroundings. Numbing or removing the (nerve)tissues b or organs, or knocking out genes, thought to form the basis of a magnetic sensory system allows the localisation of body parts involved (e.g. [7] or [8]). Direct alteration of the perceivable magnetic field can be achieved by attaching magnets to the body (typically the head c, e.g. [9] or [10]) or placing magnets in the near environment (e.g. [11]). Magnets are thought to disrupt magnetoreception, leading to impaired orientation and navigation. In contrast, controlled manipulation of field cues (intensity, inclination and polarity angles) using magnetic coil systems d enables experimenters to predict directions of movement inside the altered magnetic field (e.g. [12] or [13]), or even outside of a coil system if the effect on the biomagnetic sensory system is longer lasting such as after a so-called magnetic pulse (e.g. [14]), or in the case of a compass system which is calibrated for later use (e.g. [14]). Credit: The European Physical Journal Special Topics (2023). DOI: 10.1140/epjs/s11734-022-00755-8
For over 50 years, scientists have observed that the behavior of a wide variety of animals can be influenced by the Earth's magnetic field. However, despite decades of research, the exact nature of this 'magnetic sense' remains elusive.
Will Schneider and Richard Holland from Bangor University in Wales and their co-worker Oliver Lindecke from the Institute for Biology, Oldenburg, Germany have now written a comprehensive overview of this cross-disciplinary field, with an emphasis on the methodology involved. This work is now published in theThe European Physical Journal Special Topics.
This magnetic sense, or 'magnetoreception', was first noticed in birds, and particularly in migratory songbirds. It has now been observed in many other species including mammals, fish and insects. However, the exact relationship between the magnetic field and the behavior is difficult to pin down because it can be masked by other environmental factors. Experiments must be very carefully designed if their results are to be statistically sound.
"We aim to provide a balanced overview for researchers who wish to enter this exciting area of sensory biology," explains Schneider. He and his co-authors outlined a range of methods that are used to deduce whether an animal's behavior is affected by a magnetic field.
These include using GPS to mark animals' alignment with the Earth's field during normal activities, such as cows grazing; observing behavior after tissues thought to be responsible for magnetoreception have been removed, or genes knocked out; and attaching small magnets on or near the animals' bodies to disrupt the mechanism. Further work by animal physiologists, neuroscientists, geneticists and others will also be necessary to truly understand this phenomenon.
And this research is not only of academic interest. "Understanding animal magnetoreception will help us to protect animals released into unknown environments in the wild," adds Lindecke.
More information: Will T. Schneider et al, Over 50 years of behavioural evidence on the magnetic sense in animals: what has been learnt and how?, The European Physical Journal Special Topics (2023). DOI: 10.1140/epjs/s11734-022-00755-8
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