Eyes “see” Magnetic Fields

Biological Strategy

Garden warbler

AskNature Team

Image: Steve Garvie / Wikimedia Commons /

Sense Electricity/Magnetism From the Environment

Some living systems use electric or magnetic signals as a way to receive information from their environment. Magnetic and electric fields can help such living systems determine direction, altitude, or location, and electric fields also help living systems find other living systems. Detecting and interpreting electrical and magnetic signals requires specialized techniques. For example, mud-dwelling bacteria use crystals composed of magnetite to sense geomagnetism, which helps orient the bacteria to burrow deeper into the mud.

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Navigate Through Air

Although free from many of the physical obstructions found on land and in water, organisms that move through the air must still avoid hitting each other and objects in their flight path, such as trees and mountains. They also need to navigate from one place to another, which presents a different challenge. They use one strategy to navigate around obstructions and another to move towards their destination. For example, bats use echolocation to detect both obstacles and prey. To navigate during migration, bats also use vision, sun orientation, and likely other strategies.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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Photoreceptor neurons in the eyes of some birds help navigation by detecting magnetic fields using magnetic sensing molecules called cryptochromes.

“Birds also possess an even more remarkable visual talent — they can actually see the Earth’s magnetic field…Most scientists theorize that the bird’s perception of the magnetic field looks like two color-coded spots overlying the bird’s normal vision. These dots correspond to the north and south poles, but can be seen by the bird only in certain wavelengths of light, usually the violet end of the visible spectrum. They may vanish entirely in light wavelengths at the red end of the spectrum, depending upon the species.” (Shuker 2001:49)

“Due to the fact that a known visual pathway connects the only brain
structures that have been shown to be active during magnetic
orientation, our findings strongly support the hypothesis that
migratory birds perceive the magnetic field as a visual pattern and
that they are thus likely to “see” the magnetic field.” (Heyers et al. 2007:4)

Last Updated August 18, 2016

References

Book

The Hidden Powers of Animals: Uncovering the Secrets of Nature

26/02/2021 | Dr. Karl P. N. Shuker

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Reference

Journal article

A visual pathway links brain structures active during magnetic compass orientation in migratory birds

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