Bird compasses: an exploration of avian uses of electromagnetic fields
By Amalya
April 2025
Have you ever had the rare opportunity to see a short-eared owl perched in a tree as you wander about Scotland and wondered how did he get there?
Short-Eared Owl flying by the Old Course. Source: Ian Gair
I have been a part of the Biodiversity VIP for two semesters now. A big part of our weekly activities are bird walks around St Andrews, along the Kinness Burn, East Sands, up to the Eden estuary. I have personally seen my bird identification skills grow with every bird walk, especially this semester with the birds returning up North for Spring.
I have fallen in love with the fleets of goldfinches, the chiffchaffs who fill the tree with song, and the coal tits that land on branches above my head. I have always had a fondness for these small, flighted individuals and now can admire them with a new understanding and sense of wonder. Their appearance in our spring is part of a true wonder, as many of them do not spend the winter here in Scotland. They have travelled from the warmer south with such precision, the likes of which we can never imagine even in the age of satellite maps and GPS.
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We in St Andrews are privileged to host a wide variety of migratory birds, primarily wintering in the African continent. The owl you see will be part of a huge system of birds that relocate, some of them without having previously followed the route taken by their ancestors, sometimes with the precision of nesting in the same tree year after year.
Consider the goldfinch, a smaller bird with a delicate appearance, which left us in the fall, braving the winds to head south to Iberia or even Morocco in search of a bit of warmth and vitamin D. Many tits, such as blue tits and coal tits, tend to take a shorter journey and seek shelter in woodlands of Europe, coming back to the coast as the days get longer.
A Blue Tit perched a tree. Source: Amalya Salamo
There are several hypotheses attempting to shed light on how birds know where to go as they migrate. Some speculate that birds have enhanced hearing capabilities; an owl flying from Canada to Mexico could be simultaneously able to hear the waves of the Atlantic crashing into the east coast out of their left ear and those of the Pacific in the west from their right ear. Another idea is that they are connected to the Earth’s electromagnetic field, with scientists finding magnetic elements, like iron, in birds’ upper beaks which might help perceive and navigate these fields.
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Though tantalising, neither of these mechanisms have been found to be directly connected to the brain and thus they do not satisfactorily explain how birds migrate. Another theory that has some traction is that the visual system is enhanced in a way ours is not and this permits birds to read electromagnetic fields as well as seeing objects as we do.
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Experiments done on European robins have demonstrated that when exposed to blue light, cryptochromes, or sight sensitive proteins found in the retina, allow birds to essentially ‘see’ magnetic information superimposed on their normal vision. This becomes an actuality in the most fascinating way: after exposure to light, the cryptochrome proteins absorb it and are disrupted causing electrons to shift and form ‘unpaired’ electrons, called a radical pair. Oddly, while still separate, their behaviour and rotation remains linked and is influenced by the direction and strength of Earth’s magnetic field. This sort of connection between two subatomic particles, in this case the electrons, is called quantum entanglement. This is a phenomenon usually discussed in theoretical physics, and this is one of the few known examples of quantum physics directly affecting biological processes.
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Although disconnected, particles in quantum entanglement become linked so that the state of one instantly influences the state of the other, even if they’re far apart. These separate pairs of two electrons spin in response to the influence of Earth’s magnetic field, altering their behaviour. Just like the photoreceptors on our eye cells react to light, the cryptochromes in the bird’s eyes detect the changes in the paired electrons and so this enables the bird to detect the Earth’s magnetic field. The bird’s visual system can then interpret these changes as it flies, using the magnetic ‘sight’ to create a sort of patterned map that can guide them to stay on course during migration. Imagine bands of colour materialising on the landscape below, almost like lane markers on a road.
The above diagram shows how light photons tigger the formation of radical pairs that enable robins to navigate with Earth’s magnetic field. Source: Nature
Scientists are still working to discover how widespread this phenomenon is among species, as well as the degree of sensitivity the mechanism has to environmental disruption. Light pollution does interfere with the activation of cryptochromes, preventing birds to properly connect to magnetic field maps. Similarly electromagnetic interference from man made technologies such as 5G towers and power lines, can throw these birds off. Additionally, climate change has been impacting migration patterns and the habitats of birds, but it is unclear if that has to do with shifts in the magnetic field, it’s perception by the migrating birds, or another set of factors. Armed with an understanding of these hidden mechanisms, scientists can get a better understanding of the rhythm of migration, and conservationists can advocate for better infrastructures.
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Although I was not fortunate enough to see our elusive short-eared owl, I am in awe that even without seeing the magnetic fields that guided it back to the Old Course, I am able to witness the presence of others who have made the journey north to us in St Andrews. I feel a shift in my experience of everyday nature, I have always enjoyed the flutter of bird song, but now I know what a privilege it is to hear their sweet tunes and can really appreciate the journey these birds have taken for me to experience them.
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So next time you take a walk about town, I urge you to take the time to admire the birds, listen to their song, and wonder in the unravelling mystery that brought them to our boughs. I am so drawn to the hidden intricacies of nature, zooming into the particles, spinning behind birds’ eyes. I can appreciate the picture in front of me, layered with invisible maps, centuries of instinct, and the grounding pull of Earth’s magnetism.
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Now I leave you to consider every flap of a wing, every jump of a robin, every chirp of a chiffchaff, as more than just bird stuff. These incredible animals have the ability to look beyond our visual spectrum, experience the world in such a different way. Maybe if we all took even just a moment to pause and admire, we too can be let in to their secrets.