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| Earth on May 07, 2012

Experiment shows pigeons perceive a magnetic signal

Birds have long been suspected of using Earth’s magnetic field to navigate. A new experiment demonstrates that pigeons do process a magnetic signal.

Artist's concept of lines of force in Earth's magnetic field. Image via Drs. Dickman and Wu

Can animals perceive magnetic fields? This question has intrigued biologists and others. Our eyes, of course, are simply antennas capable of detecting particularly useful frequencies of electromagnetic waves, or light. Why should animals not also possess magnetic receptors somehow tuned to our Earth’s magnetic field?

Researchers at the Baylor College of Medicine in Houston, led by Dr. J. David Dickman, have taken steps to answer this question in the affirmative. They concentrated their research on pigeons, which have long been suspected of having magnetic perception to aid their navigation. By examining neural activity in the brain stems of pigeons, Dr. Dickman and Dr. Le-Qing Wu were able to correlate the birds’ neural activity to a changing magnetic environment, thus demonstrating that the birds were processing a magnetic signal. A report describing their results appeared online on April 26, 2012 in Science Express.

Drs. Dickman and Wu were also able to correlate the rate of neuron firing to different orientations of the applied magnetic field. This is an effective proof that the birds are not only aware of the direction of magnetic north, but also their latitude as the up/down orientation of Earth’s magnetic field changes as one travels north or south.

Yet a big question remains. What is the mechanism by which these birds and other animals might receive magnetic signals? This question is the subject of debate. A diverse group of animals, ranging from turtles, to birds, to newts and lobsters, have been identified as having magnetic perception from behavioral studies. These studies generally involve the subject placed in a controllable magnetic field and noting how their behavior changes as the field changes. Pulling from such a diverse group of animals increases the difficulties of identifying a common mechanism for magneto-perception, if one exists at all.

Doves and pigeons in flight. Image via Shutterstock

Another difficulty in identifying how these fields are initially received by the animal is that magnetic fields permeate our bodies. They are in no way blocked from the interior of our bodies by skin like other signals animals receive such as light, smells, and tactile sensations. Therefore, magnetic field receptors could be located anywhere in their bodies, not just on their exteriors, for example, their eyes.

A few ideas have been proposed. One that applies to animals constantly on the move, such as fish, is the possibility of electromagnetic induction. Faraday’s Law, one of the laws governing electric and magnetic forces, states that magnetic fields passing through a circuit will produce a voltage and current through that circuit. This could be a mechanism animals use to detect magnetic fields.

Another possibility is that animals possess small samples of magnetite, Fe3O4, a naturally occurring magnetic ore. As a magnetic field is applied to magnetite, it will twist around to align itself in that field just as a compass does. It is possible that the ore is attached to tiny hairs similar to the ones found in our ear and as the ore tugs on the hairs, an signal is sent through the nervous system.

Finally, there are some chemical reactions that become favorable under the application of magnetic fields. These reactions could be used to discern directionality of applied magnetic fields.

Dickman and Wu’s study represents one of the first neurological studies of magnetic perception. They placed electrolytic lesions, basically a conductor connected to a voltmeter, to different locations within the brain stem of the pigeons. This allowed them to monitor not only which areas of the brain stem were responding to the magnetic stimulus, but also to the strength of the response. They found the strength of the response changed with the orientation of the applied magnetic field. Also, they observed that the strength of the neurological response was greatest when the field strength was approximately the same as Earth’s magnetic field.

This fascinating study might be one step in realizing that we as animals might possess more than our recognized five senses.

Bottom line: Drs. J. David Dickman and Le-Qing Wu at the Baylor College of Medicine in Houston, Texas examined neural activity in the brain stems of pigeons to show that these birds to process a magnetic signal.