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There is a board game from the 90's called 'Mind Trap' in which players must solve tough riddles. One of the riddles goes like this:

Sid Shady claimed that he developed a special insulation for high powered electrical lines. He said the insulation is guaranteed to save thousands of birds who unwittingly land on the lines and are electrocuted each year. [..] What was wrong with Shady's claim?

The solution was:

High powered electrical lines have such a strong magnetic field that is virtually impossible for birds to land on them. The magnetic field will actually repel the birds.

That sounds like hogwash to me. However, over the past few years I've noticed I have never once seen a bird sitting on a high-voltage power-line.

So, are birds really magnetically repelled by high-voltage power lines?

Someone here asked the same question, and the consensus seemed to be that birds don't land on the wires because "a bird's sense of direction is governed by magnetic fields."

However, note that they also concluded that the birds wouldn't be shocked by the wires because they're not grounded, which I'm fairly certain is incorrect.

BlueRaja - Danny Pflughoeft
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    Anecdotal: I see birds sitting on HV (15kV) power lines all the time where I live. Jackdaws or some kind of thrushes. – Emanuel Landeholm Apr 12 '14 at 21:13
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    @EmanuelLandeholm: I would still consider 15kV as 'residential'. The lines I've always understood to be 'HV-lines' are the long-distance lines you see between cities of 100kV and up. Wikipedia calls them ['transmission lines'](http://upload.wikimedia.org/wikipedia/commons/4/41/Electricity_grid_simple-_North_America.svg) – BlueRaja - Danny Pflughoeft Apr 13 '14 at 02:34
  • http://www.fws.gov/birds/documents/powerlines.pdf – Fattie Apr 13 '14 at 08:35
  • @JoeBlow I think you went overboard on the comments.. anyways, the statement *"you have to touch both a positive and a negative to get a shock"* is wrong in several ways. First of all, there is no positive/negative in AC. Secondly, you **will** get a shock if you touch an HV line, because at such high voltages the simplistic view of *"electricity goes from hot to ground"* breaks down. Electricity will flow because you, like all things, have a capacitance. That's why in the video I linked they need to neutralize before working. See [here](http://physics.stackexchange.com/questions/74625). – BlueRaja - Danny Pflughoeft Apr 13 '14 at 16:15
  • @JoeBlow Please see my video in the question. You do *not* need to touch two lines, and the shock is *not* small. You would need to touch two lines to have a *continuous* electrical flow, but the shock that occurs when neutralizing your voltage only requires touching one wire, and in HV lines, it can be very large. – BlueRaja - Danny Pflughoeft Apr 13 '14 at 18:32
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    Regarding the "helicopter effect" seen in your excellent video (I've seen this before). Can anyone explain why they does not happen to birds? The language used to describe it in the video is inaccurate. Why do they ground off the chopper (notice the alligator clip) which doesn't make sense based on the other? So, "and the shock is not small" = why are birds not affected like the chopper? – Fattie Apr 13 '14 at 18:53
  • @JoeBlow Voltage is a relative measurement; "absolute voltage" is called 'electric potential'. The helicopter/person have one potential, the wire has a different *(average)* potential. When there is a difference in potential, aka a voltage, electricity flows. This is what causes static shock. If the operator did not slowly equalize himself/the helicopter to the wire, he'd get an enormous shock when he touched the wire. It **must** happen to birds as well; the question is just how quickly *(if their bodies have high enough resistance, it could happen slowly enough that they don't feel it)*. – BlueRaja - Danny Pflughoeft Apr 13 '14 at 21:56
  • Hmm, seems strange to me. Every physicist is annoyed that electrical engineering is so tricky :) Then why do they ground-off the chopper (note the clamp)? Why? And it makes not much sense that birds "have more resistance". Thirdly they talk about that spark being "1/2m volts" which is the three phase power level, no connection to what you describe. I dunno! – Fattie Apr 13 '14 at 22:03
  • @JoeBlow: ..The helicopter is not grounded. There's a clamp connecting the worker to the helicopter so they all stay at the same electric potential, but if the helicopter were to become grounded, it would cause a short through the worker, likely killing him. You are correct that the terminology they use in that video is incorrect. If you have any more questions, please ask on the physics or EE stackexchanges, this is not the correct place to be discussing this. – BlueRaja - Danny Pflughoeft Apr 13 '14 at 22:15
  • Hi Blue .. no, I meant "grounded to the cables". (Like when you "ground" something when working on your car.) Just as you say. I don't see any way they could change potential, after he "zaps" them, is there a way? Youi're quite right about the EE site. Cheers for now and bye. – Fattie Apr 13 '14 at 22:24
  • Indirectly related: [Recent answer on physics.SE](http://physics.stackexchange.com/a/109160/31888) detailing the actual danger of standing on a power line to the bid. – Brian S Apr 21 '14 at 16:25
  • @BlueRaja-DannyPflughoeft My mistake, these are not residential lines. I'm not sure if they rated at 400kV or 100kV, but they are much higher than 15kV. – Emanuel Landeholm Apr 24 '14 at 13:55

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The premise of the question is wrong and the science of electromagnetism suggests why

A simple google search for images using the term "birds power lines" will show many pictures revealing birds sitting on power lines such as this one (source is here):

birds on power lines

Or, for those who think only high voltage power lines are the issue, this one (source):

birds on HV power lines

This demonstrates two things:

  • birds are not repelled from power lines
  • birds are not electrocuted by sitting on power lines

So the premise of the question--birds don't sit on power lines--is demonstrably wrong.

We could probably work this out by noting the actual magnetic fields around power lines are small (see here for actual numbers and note these are millions of times smaller than the fields in medical MRI scanners which don't repel the people they scan who are made from the same stuff as birds). To clarify for those who referenced the youtube videos of diamagnetic levitation, the issue is about field strength and the magnitude of the force. Small animals and diamagnetic objects can be levitated in extremely strong magnetic fields (say 10 Tesla or so, similar to the fields used in the largest MRI scanners which don't cause enough force for even a medium sized animal to notice). The fields around power lines (which you could calculate for yourself from basic physics) are a few micro-Tesla even near the line. This is a million or so times smaller than the fields used to levitate small diamagnetic objects and weaker than the earth's magnetic field which varies from around 25 to 60 micro Tesla.

The birds also don't get electrocuted as they have no path to earth.

It is possible that even a small field could disrupt a magnetic sense of direction (as some birds are thought to have), but the field decays rapidly with distance and birds don't need to navigate when they can see where they are so the idea is, again, implausible.

matt_black
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    Sorry, but I have to give this -1. The power lines shown in your google-search/picture are residential power lines, not high-voltage power lines. Also the claim that other animals *(assuming that's what "made from the same stuff as birds" means..)* cannot be repelled by strong magnetic fields [is false](http://www.youtube.com/watch?v=A1vyB-O5i6E). And your last paragraph is unsourced speculation. – BlueRaja - Danny Pflughoeft Apr 13 '14 at 02:24
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    @BlueRaja-DannyPflughoeft yes strong magnetic fields can repel diamagnetic objects but wires don't produce fields strong enough to even notice the effect. Your demo uses fields at least a million times stronger that HV transmission wires produce. Also it is current not voltage dependent so the difference between big and small transmission wires is not that big. Moreover birds do sit on HV wires. – matt_black Apr 13 '14 at 12:35
  • This edit is better, I'll remove my -1. However, the statement *"The birds also don't get electrocuted as they have no path to earth"* is incorrect. They would shocked when they neutralize with the power-line, even if there is no path to ground; if they don't, their bodies must have exceptionally-high electrical resistance. See [the link in the question](http://www.youtube.com/watch?v=9Lbmis-VUW0#t=4m50s), as well as [my comment above](http://skeptics.stackexchange.com/questions/20218/20221?noredirect=1#comment78288_20218) and [this link](http://physics.stackexchange.com/questions/74625/). – BlueRaja - Danny Pflughoeft Apr 13 '14 at 16:20
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    matt - your second image is totally awesome, and answers the question "in fact, do birds sit on HV lines?" that question is answered! – Fattie Apr 13 '14 at 16:29
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    @BlueRaja-DannyPflughoeft Strictly speaking you are correct on the electrical point, but whatever the effect is the birds don't seem to notice. There is some, very small, AC and DC charge transfer to the birds as they won't have *exactly* the same average potential as an HV power line. But both are minuscule. The AC current will be roughly the same as the loss to ground from the wire (as the bird makes little difference to the resistance to ground) and the DC transfer will be even smaller as, crudely, birds are not big capacitors. – matt_black Apr 13 '14 at 17:02
  • Nevertheless Matt: given that on this site the aim is ultimate argumentative rigour. Your final paragraph is just saying "you think" the fields involved are "very much smaller" than what could disrupt supposed bird magno-sense. (Indeed, it is 100% possible that - IF bird-magno-sense does exist - and, sitting on HV lines, DOES, in fact, completely disrupt bird-magno-sense, then, quite simply that does NOT bother them ("repel them" sense2) and indeed they are happy to sit there even though it turns off their bird-magno-sense.) (Again, you've proven with photos they are NOT "repelled" sense2). – Fattie Apr 13 '14 at 17:28
  • @JoeBlow Please plan what you want to say more carefully, your excessive comments are making it very hard to follow the conversation. – BlueRaja - Danny Pflughoeft Apr 13 '14 at 18:40
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    It is also worth noting that magnetic lines around the wires can't repel anything (if it doesn't carry a current) because they are not directed outwards, but are circular: http://www.pa.msu.edu/courses/1997spring/phy232/lectures/ampereslaw/wire.html – sashkello Apr 14 '14 at 01:41