Sharp-eyed robins can see magnetic fields

Jul 09, 2010 by Lin Edwards report
Sharp-eyed robins can see magnetic fields
A Robin Wearing Goggles

(PhysOrg.com) -- It has been known for decades that some birds are able to sense the Earth's magnetic field and set their direction as if following a compass heading, which is an extremely useful ability for birds migrating long distances. The ability is believed to be linked to the availability of light and it is thought that specialized molecules in the birds' retinas allow them to literally see the magnetic fields, which appear as patterns of light and shade superimposed over the regular image from light. Now a new study shows that the internal compass also depends on the birds having clear vision in their right eyes.

Researchers led by Katrin Stapput of Goethe-Universitat in Frankfurt, Germany, studied the vision of the European robin to try to learn more about how the magnetic sensing might work. They found that if the right was covered by a frosted goggle, the could not navigate effectively, while they could navigate perfectly well if the left eye was covered instead.

Numerous studies have been carried out on the ability of birds to sense magnetic fields since the phenomenon was first discovered in 1968 in the European robin. These studies had already revealed that the sense depends on light and that it involves the right eye and the left side of the , but the details were still unclear.

The most likely molecules involved in the sensing of magnetic fields are thought to be cryptochrome and flavin adenine dinucleotide (FAD), which are found in the light-sensitive cells in the retina. When struck by blue light, cryptochrome and FAD both shift into an active state in which each molecule has an unpaired electron, creating a “radical pair.” The presence of magnetic fields affects the time it takes for the radical pair molecules to revert to their inactive state.

also affects the light sensitivity of , which suggests it may also affect sensitivity to magnetic fields. In effect, the magnetic fields create light or dark shadings over what the bird usually sees, and the shadings change as the bird turns its head, giving it a visual compass from the patterns of shading.

Stapput decided to test the theories by fitting robins with goggles that were covered with clear foil on one side and frosted foil on the other. Both sides of the goggles were equally translucent, allowing 70 percent of the light to get through, but on the frosted side the image was less clear. The birds were then kept in cages until it was time for them to migrate.

The birds were released into a funnel-shaped cage with its walls painted with correction fluid, which was scratched if the birds touched them. The results were that birds with no eye coverings, and birds with the left eye covered set off in a northerly direction as expected, while those with the right eye covered were disoriented and headed in random directions.

Stapput's experiment is the first to show that magnetic sensing does not just depend on light being present as previously thought, but that the bird must have a sharp, focused image in its right eye. The magnetic sensing is overlaid over the normal vision, and if that is distorted, Stapput said the patterns of light and dark would make little sense since the bird cannot separate the information from the visual and magnetic images. The visual and magnetic images both involve variations in light and shade, but visual images tend to have sharp lines and edges, while the magnetic images have more gradual changes from light to dark.

The experiments lend support to the radical pair hypothesis but do not rule out another explanation.

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More information: Magnetoreception of Directional Information in Birds Requires Nondegraded Vision, Katrin Stapput et al., Current Biology, doi:10.1016/j.cub.2010.05.070

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User comments : 15

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Bob_Kob
4.9 / 5 (7) Jul 09, 2010
Thats amazing, I wonder if humans have something like this, perhaps hidden away or not switched on.
Skeptic_Heretic
5 / 5 (3) Jul 09, 2010
Thats amazing, I wonder if humans have something like this, perhaps hidden away or not switched on.

There is, but on the other end of the spectrum. Something like 1% of women have hyperchromatic vision. Effectively they can see just a speck of the Ultraviolet wavelength.
Verteiron
3.8 / 5 (5) Jul 09, 2010
Skeptic, I believe you have misinterpreted 'tetrachromatic' vision. This may affect as many 2%-3% of women worldwide. These women can perceive a fourth "primary" color between red and green, giving them incredibly accurate color vision. It is very easy for them to distinguish between clothing dye lots and paint samples that look identical to normal, trichromatic vision. Unfortunately, as a result of this mutation, their sons tend to suffer from red/green colorblindness.

Sadly, human vision into the ultraviolet is impossible under normal circumstances due to the human lens being opaque to UV. In cases where the lens has been removed, however, UV light can be perceived directly. It is described as appearing white with a faint blue tinge to it.
A_Paradox
5 / 5 (3) Jul 09, 2010
Thats amazing, I wonder if humans have something like this, perhaps hidden away or not switched on.

Bob Kob, amazing indeed! As for humans, I think not. Prior to reading this I thought that crystals of magnetite were the only method that animals had available to detect magnetic fields. This system sounds to be much more sensitive though.

Intriguing also that it is only the right eye and left hemisphere involved.
ffrankblu
not rated yet Jul 09, 2010
I can see little dancing motes of blue-white light out of the corners of my eyes at times but if I focus on them they dissipate.I thought they were quantum particles.
Skeptic_Heretic
5 / 5 (2) Jul 09, 2010
Skeptic, I believe you have misinterpreted 'tetrachromatic' vision. This may affect as many 2%-3% of women worldwide. These women can perceive a fourth "primary" color between red and green, giving them incredibly accurate color vision. It is very easy for them to distinguish between clothing dye lots and paint samples that look identical to normal, trichromatic vision. Unfortunately, as a result of this mutation, their sons tend to suffer from red/green colorblindness.
Actually I used the wrong word but you're going off of an older study on the same topic. The "false yellow" cones created by dual X chromosomes are only one aspect of human tetrachromats. We've found that a very small percentage of tetrachromats show a subtle shift to UV in some cases. As you say the lens is opaque for most of us, but we understand that is not entirely the case for all people. There is a rather large variance in lens opacity.

A lot of this research I picked up from reading on synesthesia(sp?)
Skeptic_Heretic
5 / 5 (2) Jul 09, 2010
Found the paper but I don't have an online copy. Griswold & Stark is the primary dataset, which I can't find online. Tan is the originating paper, which I only have in hardcopy as it's from 85 and here's a similar paper online.
http://www.scienc...32e15b00
skm23
not rated yet Jul 10, 2010
I can see the activity in UV light- it's like billions of translucent circles bumping into each other at high speed- this sounds so weird, but I've been able to see this activity in light since I was a child-I don't know what it means or even what it is~
vonrock
1 / 5 (1) Jul 10, 2010
Yeah, They can see the magnetic field in all it's splendor, I was talking to one last night explaining how it heard FM radio on certain nights too. I smoke the same stuff as skm23
marcin_szczurowski
not rated yet Jul 10, 2010
I work on waveguides and fiber optics. We use wavelengths around 850nm, which appears to as 'fuzzy' red if there's high enough intensity (can't focus it correctly). For years I believed that it's normal (sensitivity tail) but lately it came out that not everyone see the range 800-850nm. That shift is only towards NIR in my case. I don't know is it a mutation in opsine or only different concentration but for sure, none of us see (taste and feel) the world the same.
Seeing magnetic field would be interesting 'feature' but evolution probably ruled it out in our case :(
FredJose
1 / 5 (1) Jul 10, 2010
Seeing magnetic field would be interesting 'feature' but evolution probably ruled it out in our case :(

Speaking of evolution, just how did reptiles develop into birds with this kind of navigational ability?
That would be very interesting to know.
jt81ma
not rated yet Jul 11, 2010
I'm wondering how large the test group was. This sounds akin to "handedness" in a way, moreso than one eye or brain hemisphere being strictly responsible. What I mean is, take for example that as with humans and apes preferring one hand over another (and being primarily right handed mind you (ie left brain dominant)), could this also be the case with their ability? Could it simply be that the test subjects were all left brain dominant and developed this sensitive, innate ability in the dominant side only for precision?
Husky
not rated yet Jul 11, 2010
I wonder if birds could also sense approaching lightning from the electromagnetic fields that might be superimposed before any visible lightning actually strikes, i know birds tend to fly low in the prelude to a thunderstorm and i thought it was due to them sensing turbulence in upper air layers, but perhaps this is another factor
Husky
not rated yet Jul 11, 2010
believe it or not but I firmly believe i can reasonably accurately smell the north with my big nose, my nostrils tense and widen and if some is touching my nosebone gently, it works even better witrh my eyes closed to shut out other interfering senses / thoughts
adaptation
5 / 5 (1) Jul 11, 2010
"Billions of little translucent circles" and "little dancing motes" are most likely the vitreous of your eye(s).

That's really interesting Husky. I haven't much considered the mechanism behind humans' sense of direction.

Perhaps we should prepare ourselves for the upcoming article entitled "Humans Smell Magnetic Fields...Who Knew?"