Farmers and herders have known for centuries that herds of cattle have an uncanny ability to all point in the same direction. Last year, a group of German and Czech scientists discovered the reason behind this alignment - unbeknownst to humans for thousands of years of domestication, these animals have a magnetic sense. The team used Google Earth satellite images to rule out alternative explanations like the wind and the sun, and show that cow and deer herds tend to point towards magnetic north like a living, hoofed compass needle.
Now, the same team have found that high-voltage power lines, which emit strong magnetic fields of their own, disrupt the orientation of cattle and deer. Near these lines, their neat alignment goes astray and they position themselves at random. This disturbance becomes less and less pronounced as the animals stray further away from the power lines. This is yet further proof that cows and deer have a magnetic sense that's only just become apparent to us.
A wide variety of animals navigate using the Earth's magnetic field as a guide, but until recently, bats and rodents (including hamsters, mice and mole rats) were the only mammals to demonstrate this sense. In fact, the ability may be much more widespread, for these groups are small and easily tested in the kinds of laboratory experiments that would be impossible with larger creatures. To study the senses of cows and deer, Hynek Burda from the University of Duisberg-Essen was forced to be more creative.
He used pictures of herds of animals taken by Google Earth's satellites to show that they line up according to the North-South poles, regardless of the position of the sun and in parts of the world with very different prevailing winds. In this new study, he made use of large magnetic anomalies caused by the presence of power lines to see if the animals' behaviour was affected.
Electrical pylons deflect the Earth's magnetic field around them in a radius of up to 30 metres. The lines running between them produce what are known as "extremely low-frequency magnetic fields" (ELFMFs). These are strongest at the mid-point where the line sags closest to the ground and decrease exponentially the further you get from the line.
Burda looked at satellite images of 153 herds of European cattle grazing within 150 metres of power lines, and found that they had no preference in their directions. In contrast, images of 111 herds in open pastures showed that they were significantly aligned along the north-south axis.
The same was true for roe deer, which the team observed first-hand. They witnessed 201 herds grazing in open areas and saw that they faced along a rough north-south axis. However, 47 herds straying near power lines were randomly aligned. Neither species was lining up to the direction of the cables themselves. These observations are powerful indicators that the animals' stances were not primarily set by the positions of the sun.
Their positions even varied at different distances from the power lines, becoming more and more natural as the intensity of the man-made magnetic fields fell. If the power lines were running in an east-west direction, individual cows directly underneath tended to face in the same east-west direction, but those standing further and further away progressively shifted to the typical north-south alignment. Likewise, animals standing under north-south power lines also tended to face in a north-south direction, although their deviation from this standard direction became less and less as they got further away.
This new study provides yet more support for the magnetic sense of cows, but why and how they do it is still a mystery. Other mammals such as mole rats and bats rely on magnetic crystals called magnetite; pigeons carry magnetite in their beaks too.
Another method - the so-called "radical-pair" hypothesis - involves a light-sensitive molecule called cryptochrome, which is used by light-detecting cells in our eyes to sense blue light. When cryptochrome is activated, it forms a pair of "free radicals" - molecules with lone, unpaired electrons. Magnetic fields can affect whether these electrons "spin" together or not, and that in turn affects how long cryptochrome stays active for. Through cryptochrome, animals may actually be able to see magnetic fields as visual patterns.
The benefits that cows and deer gain by detecting magnetic fields are just as unclear as the means through which they do it. There are many possibilities. Synchronising the direction of the herd could make it easier to graze efficiently or escape predators effectively. It could help them to navigate as they move to fresh pastures (although deer also align magnetically while they're resting). The most intriguing reason of all, which the group put forward in their last paper, is that magnetic alignment could make some bodily processes function more effectively.
Reference: PNAS doi:10.1073/pnas.0811194106
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"Synchronising the direction of the herd could make it easier to graze efficiently or escape predators effectively."
That was my first thought as well. But why align by a compass point? It would make more sense to align by the most likely direction where the predators would be coming from. Alignment requires only eyes.
Anyway, could we humans have this ability as well? It would have to be weak, but it could still exist. It would go unnoticed in the electrically driven society of today.
Whether or not humans have a magnetic sense (albeit unconscious) can be easily tested: take a bunch of random people, confuse them as to the direction they are facing (drive / walk in circles at night etc.), then lead them into a windowless room and ask them to point north. If they point prevelently in one direction (which needs not to be north), you have your answer, or at least a good suggestion.
@ Andrea M
Seems like something similar has been done already:
http://www.ncbi.nlm.nih.gov/pubmed/7423208?dopt=Abstract&holding=npg
Quite fascinating to think, that we also might have a magnetic sense.
Although I'm leery here of confirmation bias or selective observation, the observation of uniform orientation is interesting. In my opinion though, the question is not "Why do they align in the same direction?", but "Why do they align north-south?" I suggest a thermoregulatory effect. N-S orientation means that the animals' bodies are aligned (more or less) perpendicular to the sun in the morning and evening, so they maximize the amount of solar energy (=free heat) during the cool parts of the day. [N-S orientation also makes the animals' bodies parallel (along the ground,at least) to the sun around noon, so that they minimize heat absorbed and avoid overheating, but I am not so sure that this effect would be important, because they have other ways to avoid overheating.] A similar explanation has been proposed for termite mounds in Africa, which are built with their long axes N-S, and thus get the same benefits as I've proposed.
I seem to recall reading an article which discussed the discovery of magnetite in vertebrates' spinal columns. The gist was that single-celled organisms having magnetic sense gave rise to vertebrates by having the spine develop on the "backbone" of magnetite.
Thus I wonder: perhaps magnetic sense in cows and deer may simply be a side-effect of being vertebrates with no selective advantage.
Cows practice Feng Shui?
DJlactin - the sun theory has already been discounted by this group's previous paper
Ed: Not really:
They weren't using the sun to get their bearings ; however, the N/S orientation (based on magnetism) may still have the benefit of placing the animals perpendicular to the sun in the early or late day.
Free heat from the sun is a valuable resource: it warms your body without requiring you to burn fuel captured at low efficiency by primary producers and passed up the food chain at low efficiency, then stored at low efficiency and burned at low efficiency.)
... in the choice of orientation. Orienting N/S at night positions them properly to receive maximum insolation when the sun rises.
Of course, my hypothesis (not "theory"!) is simply armchair stuff (albeit from a person whose specialty was behavioral thermoregulation).
Coming back to my question in my earlier post: "Why N/S?" (as opposed to E/W or ...). I can't think of any other explanation that "answers" this question.
Hmm, interesting point about the pylons. Does that mean that wooden poles would have less of an effect than metal poles (pylons)?
As for the magnetic fields produced, this depends on the current through the lines, and the current through the lines is lower for higher voltage lines. Thus, I would expect more of an effect for lower voltage distribution lines than high voltage transmission lines.
Also, note that, for a balanced power transmission system, the magnetic field produced by one line should be negated by the magnetic fields produced by the other lines (although there is a slight amount of mismatch due to the spacing of the lines).
One wonders, though, whether a good test of this would be to monitor some cattle in a field with an artificial magnetic field (e.g., permanent magnets spaced throughout the field, or Helmholtz coils, although they'd be pretty large).
Dave
Wow. This is so interesting. No answers yet--but fascinating.
Cool post. I'll have fun with this for ages. If this is peer reviewed and published science, is there a link or reference you could post? I tried to search on the doi/pnas numbers and found only a german site that I don't understand.
Ryan, it is indeed peer-reviewed and published. PNAS have an annoying habit of lifting embargoes on papers up to a week before it's actually published. Try that doi number again over the next few days - it should come live soon.
I'm curious about different effects on AC vs. DC transmission lines. The former would have a confused magnetic field, where the latter would have an extremely strong and stable field. Probably the latter is much less common, and observations mostly or entirely involved AC.
It would also be very interesting to determine whether they are responding to the horizontal field orientation, like a compass, or to the inclination, as found in birds and, I think, insects. This should be determinable from their behavior around DC transmission lines.
Nathan - They focused on AC lines only. There's a lot of detail in the paper that I haven't included here, including lots of data on orientation and inclination. Worth having a look when the paper comes out.
I had wondered whether power lines would screw up birds' magnetic sense. I guess the answer is yes.
I really liked this post. It makes me think about human "discoveries", when all we are doing is finally getting a better understanding of what already exists.
Nearly all animals can sense magnetism. Just because we humans may be less sensitive to it than other species, possible because the part of the brain that controls intellect is also the part of the brain that controls instinct, it doesn't mean that this phenomenom is that the use of magnetism is unusual.
Bees, ants, birds, bats, caribou,some humans, all utilize magnetism as a force in the interrelationship with our planet.
Thanks for the reminder. I like this kind of stimulus.
Hum... the DOI doesn't work for me... How come?
"I suggest a thermoregulatory effect. N-S orientation means that the animals' bodies are aligned (more or less) perpendicular to the sun in the morning and evening, so they maximize the amount of solar energy (=free heat) during the cool parts of the day."
Why invoke magnetism for this? The cow can simply sense the suns heat via skin receptors... that way it could follow the sun at all times, which would be much more efficient than always pointing north-south. Termite mounds cannot move or sense and thus the two cases are rather different.
Animals that have magnetic sense seem to very often have migratory habits. I would suggest that these magnetic senses and North-South orientation have to do with the North-South migratory patterns that Bovid and Cervid heards had in the past.
I'm fairly sure I've read work showing that monarch butterflies also have this sense.
... I should probably clarify, I didn't mean to imply that the cow always wants to maximize solar exposure. That they continue on a North-South gradient should show that thermoregulation is not primarily being done via the sun in this case... these are mammals, after all. Staying close to others is probably a much better way to stay warm.
Oh, and from a quick literature search the magnetism in monarchs appears to be fairly contested.
What a great study! Science by google earth. But let's not forget that not all traits/behaviors are adaptive. There might not be any benefits at all.
Given that the pigeon family, and I assume doves, etc. have and use the magnetic lines of force to navigate, that they would find it uncomfortable to have their compass scrambled by changing proximity to 60 cycle AC power lines as they fly near... Yet I notice that they seem quite fond of standing and walking on the lines during the day, apparently finding the pleasure of easy roosting to outweigh any discomfort...
We have cattle and I have never noticed anything like described in this article. I have noticed that the cattle do sometimes seem to follow the power lines as they eat but this is more due to the fact that the there is a band of grass that has underbrush controlled by the power company thus allowing for an easy access for the herd to graze. If they are not in a area with power lines, they basically start at the same point every day around the same time of day and eat their way to the water supply, away from the water supply, toward it again, etc. This may be in a north-south, east-west or any other pattern. The cattle are affected by the sun since in the cooler times, they lay or stand much more in a pattern that exposes a larger area to the sun while in hotter weather, they face away from the sun. Trying to convince me that is is all about magnetism is a waste of both our time.
eric: the 'follow north' idea seems much too ultimate (to me!). Oriention over days would seem to trump orientation within days.
dafarmer: your cattle are under the power line; the paper suggests that any orientation effect is eliminated in this case. How do your girls move when they're away from the line?
This article should teach a lesson to those who have a uncanny habit of dismissing things as 'pseudoscience' even before they're disproved by science.
More examples in point:
While inside an MRI chamber, some people have vertigo due to stimulation of semicircular canals by high magnetic fields.
There may now be some rationale in 'electronic sleeping aids' that uses electromagnetic fields(this is in reference to your last line).
The sun, I've watched the cows point their heads away from the sun. I think it's more of a heat cooling shading thing, then a magnetism thing.
Tammy
Ever drive underneath these power lines listening to AM radio?, ever stand near them and just listen? Anyone here sensitive to EMF, or ES? How about continuous noise, like the low hum of an AC/DC converter? At least the cows are smart enough to not stare directly into the sun, I hear it can blind you.