How Do Birds Sit on Power Lines without Getting Electrocuted?
Guest post by Aaron Johnson from the Ask an Engineer series, published by MIT’s School of Engineering. Photo by Doug Waldron.
You’ve probably never seen a bird straddle two wires at once, and there’s a good reason for that…
It’s not uncommon for a character in the movies to end up with a blackened face and a headful of frizzy hair after touching a live electrical wire. What makes for a good gag in the entertainment biz, however, is likely to kill you in real life—unless you’re a bird. Birds have no problem sitting, unruffled, on the high-voltage power lines you often see lining the road. This ability has nothing to do with them being birds, explains Ranbel Sun '10, MNG '13, a recent grad in electrical engineering who currently teaches at Phillips Academy in Andover, Massachusetts. It’s all about the connections they’re making—or, more importantly, not making.
“Electrical current is the movement of electrons,” explains Sun. The movement of electrons through a device like your TV is what gives it the energy to display images and produce sound. Sun describes the long process these moving electrons take to get to your house. “The electrons are essentially being pulled from the ground by the power station,” she says. “They move through the power lines, through your TV, and eventually they make their way back into the ground from where they came.” This creates a closed loop, which is required for electricity to flow.
The other thing electrons need in order to move is motivation—or, more specifically, a difference in what’s called electrical potential. “Imagine lugging a bunch of bowling balls up a mountain,” Sun explains. “If you give them a path, the balls will naturally roll down the mountain to a lower position.” At the top of the mountain, the bowling balls (which represent the electric current) have a high potential, and they will travel down any path that becomes available. When a bird is perched on a single wire, its two feet are at the same electrical potential, so the electrons in the wires have no motivation to travel through the bird’s body. No moving electrons means no electric current. Our bird is safe, for the moment anyway. If that bird stretches out a wing or a leg and touches a second wire, especially one with a different electrical potential, it will open a path for the electrons—right through the bird’s body.
There are other perils for our feathered friends, Sun points out. “The wood pole supporting the wires is buried deep in the ground,” she says, “so it would also be dangerous for a bird to sit on the pole and touch a wire.” Read more.
Authored by Aaron Johnson. Thanks to Naveen Surisetty from Visakhapatnam, India, for this question. Visit the MIT School of Engineering’s Ask an Engineer site for answers to more of your questions.
Sun, 07/12/2015 9:20am
We could ask ourselves why are they sitting there in the first place.
Maybe it's a energy transference? we have been observing the Starlings behaviour for many years now and our theory is actually the former,we also discovered that there are massive water veins crossing at intersections where the sitting takes place.We also studied there nesting sites which were again obove major underground water crossings,we followed these water crossings and came up with wells with massive flow rates,more energy.In recent year's we have noticed that they are perching in massive pine trees next to some mobile base stations where a high pitch communication takes place.Were in Spain and this behaviour is taking place when the temprature is at it's highest usually between the hours of 2pm 4pm again we discovered high output water veins at these locations.
two instruments were used as part of the study: A OKM exp5000 ground penetration radar was used to as a visual representation of the water veins in real time.A Gigahertz HF 59B was used to capture the direction and signal output at the mobile base station.In this case the highest readings were taken in the direction from the trees in which the Starlings were perched.
Anyway it's food for thought''
Mon, 12/01/2014 9:49am
Agreed completely. The statement in the article is wrong.
There were telephone systems long ago that used earth as one side of the circuit, but certainly not power systems.
Tue, 11/10/2015 4:07pm
The picture shows them sitting on both high voltage transmission wires (75-300KV 0r s0) distribution wire (10-20KV) and either/or low voltage customer, ground/pole support or telco cables. At the lower voltages I doubt that the birds can tell the difference between ground and 120 volts. Why? because a birds body doesn't make as big a capacitor as my body does.
Other experiments have shown that migratory birds can determine magnetic north so maybe they enjoy the 60 Hz magnetic fields from the current carrying wires.
Thu, 01/16/2014 11:17am
wow - what could've been answered by one simple sentence evolved into a long lecture...technical types need to learn the art and skill of clarity and brevity...and i'm one of them :-)
Fri, 09/19/2014 4:45am
I watched a program when a technician was sitting in a helicopter holding a metal rod out to make contact on the the live wire before he could touch the live wire himself, why is that?
Mon, 05/02/2016 10:36am
I found the explanation thorough and complete. A good technical writer is lengthy so as to ensure understanding. Shorter answers run the risk of confusing those who need more.
Thu, 04/20/2017 7:48pm
There are other perils for our feathered friends, Sun points out. “The wood pole supporting the wires is buried deep in the ground,” she says, “so it would also be dangerous for a bird to sit on the pole and touch a wire..
NOT TRUE SAYS ARNTZ, WOOD IS NOT A GOOD CONDUCTOR, AND THE BIRD WOULD NOT BE IN DANGER
Wed, 04/12/2017 6:06pm
Mako, I agree.
Tue, 11/10/2015 3:42pm
While being insulated from ground potential I can feel the 60 Hz vibration on a bare copper wire connected to 120 volt 'hot' line voltage by gently touching the bare metal with my index finger. The voltage on those wires as shown in the picture is somewhere around 100 KV so even though they are insulated from both the aluminum wire and ground it might be possible that the birds feel something similar.
Wed, 04/12/2017 6:07pm
I always figured that birds don't get electrocuted because the wires are covered in rubber (a poor conductor of electricity).
Wed, 03/22/2017 3:37am
Well,i really tink d question hasn't bn answered!......if u ask a lay man d question,he'll jst tell u "hey i tink birds gat scaly feet which are as good as insulators"!....i tink datz jst it!.....and i tink datz why bats get electrocuted everytym dy touch a HVTL..
Sat, 11/29/2014 10:03pm
To bad no one who actually understands power generation like a licensed electrician. “The electrons are essentially being pulled from the ground by the power station.” This is essentially and confusingly false. The generator is the machine that changes mechanical energy into electrical energy. The electrical generator (alternator) takes advantage of a property call induction to make the electrons in the generator wires move back and forth in response to a changing magnetic field. Only an unwanted minority of the electrons actually move through the ground. The great majority move through wires unless something goes wrong which is why we ground most circuits. The grounding is done for safety. When a significant amount of electricity is traveling through the ground that is called a ground fault. A ground fault will often trigger safety equipment that will shut down a circuit.
If we were to use the ground as a major conductor "electrons are essentially being pulled from the ground ” we would be constantly replacing ground rods due to electrolysis and creating all kinds of dangerous and unwanted ground loops.
Sat, 11/19/2016 9:36am
Fascinating answer. Thanks for posting it.
Fifty years ago when high voltage lines were first put up the wires were under stress during the mounting process and would often acquire a slight permanent strain. A thinner wire had higher resistance, so the thought was that the birds could tell which parts of the wire were slightly warmer!
Sat, 11/19/2016 9:28am
It was Telegraph that used a Single Wire to transmit signals, using the ground itself as a return. The telegraph was neither AC nor DC but single pulses of Morse Code so it worked just fine. The operator translated the code and wrote out the message.
When the telephone was introduced business men said, "No thank you - we need something IN WRITING!"
Tue, 08/09/2016 3:01pm
Tue, 11/10/2015 4:28pm
Actually looking even closer the birds do not appear to be sitting on the 75-300 kv lines only on the top ground wires for the transmission circuits.
Wed, 12/24/2014 2:26pm
WARNING THERE IS NO SAFE VOLTAGE IT IS POSSIBLE TO KILL ONESELF WITH A SINGLE NINE VOLT BATTERY.
The three physical properties that govern the flow of electricity are capacitance, inductance and resistance. Depending on the particular circuit you can sometimes rule out one or two properties as being important. With the bird I ruled out capacitance and inductance because of my general experience with electricity. The surface area of the bird and the head to toe distance are the actual reasons why I believe they have little influence in this case. This leaves the resistance through air which once again due to experience I believe to be a large number but the significant factor preventing bird electrocution. I did not actually do any real calculations to prove my point and I have never heard anyone say this explanation is wrong.
With the helicopter I believe capacitance is the governing property. Why? general experience again. With a capacitor in an AC circuit current can flow with the charge (electrons) collecting and leaving the plates but never crossing them. This explains why there is a spark between the helicopter and wire but no spark between the plates (helicopter and ground or another high wire). So because the area of the metal skin of the helicopter is so large compared to the bird, capacitance became a significant factor. The rotating blades may also play a role but I'm not really sure how to assess that.
Also sparks are much more impressive than the actual power needed to produce them. I make that statement based on VanDergraph generators (lots of sparks bit little actual feelings), personal experience, and a video of a man on PCP grabbing a 2300 volt high wire while standing on a low voltage cable being covered with sparks and living to tell about it.
Tue, 02/14/2017 12:22pm
Why dont birds get shocked
Tue, 10/03/2017 12:42pm
Read the article again.
Thu, 12/15/2016 1:29pm
I really wondered that how they can do it. But I happy that they don't die
Munna Bhai Btech
Wed, 11/30/2016 12:42am
I am going to stand on a live wire with both my feet touching it. If i get harmed, i will find you and i will..... (Whatever Liam Neeson says in the Taken movie).
Tue, 11/15/2016 10:55am
I thought that on extremely large voltage lines if the birds widen the legs enough (on the same wire), they can still get electrocuted. Same for cows walking on the ground under the power lines.
Stanton de Riel
Wed, 08/24/2016 9:38am
You don't see birds sitting on high-voltage lines in nature. If you stand under some (particularly in humid weather) which dip close to the ground, you can hear corona discharge crackling. A conductor (like a protruding bird) would serve as a reverse-lightning rod on the line -- a focal point for discharge of current. Having handled a corona-discharge static-removal wand in the lab (whilst standing in two rubber wastebaskets, for safety!) I can attest that a bird would feel the field.
Fri, 05/27/2016 2:29pm
that still doesnt make much sense. No any creature or thing can do two things at the exacts same time. So one foot will always be faster than the other, even though its 0.00000000000000000001 of a second. Its still enough for a tiny bird to get electrocuted. And besides that.. are we just going to ignore the fact how smart and intuitive birds are? Praise nature! it always wins.
Sat, 01/09/2016 8:38am
Great photo. Birds only sit on the top wire, but not the lower ones, in the background tower. Why? Do utility engineers need to design the wires to withstand the weight of the birds? This photo can serve as a great topic of conversation during a job interview.
Sat, 10/31/2015 10:58am
That explains the extinction of the large flying reptiles who leg span probably was large enough to touch two wires.
Wed, 11/26/2014 10:42am
They actually DO get electrocuted - in rare circumstances, though. There have been repeated cases where storks or other large birds have been sitting on high voltage power lines and then "kissing", i.e. touching with their beaks. This of course then was the last of them ...
Tue, 07/29/2014 6:33pm
I really thought that most of the birds that are electrocuted on power lines are those that are sitting on lines which were either broken or which has a bad line.
Thu, 03/13/2014 2:04pm
I think birds all face the same direction on the power line because they need to land and take-off into the wind.
Sun, 07/23/2017 12:43am
This would seem to generally make sense given basic technical knowledge of lift and aeronautics... Nature has wisdom about things that we humans have to think about. There's a great book out there called 'What the Robin Knows.' The author learned from trackers in, among other places, the Australian Outback - and also sits and observes nature, especially birds. He relates an anecdote about being at a conference center that used to be a house, in a room with sliding glass doors looking out over a pool and patio, chatting with the other conference participants. All of a sudden, the author, in the anecdote says something like: "Cat's coming..." His conversational companions look puzzled until a cat does indeed creep/skulk around the corner of the patio. When questioned as to how the author knew the cat was there, he replied that a small bird had been on the patio and had suddenly jumped up to what the author describes as the minimum height necessary to avoid the cat, thereby burning no more scarce calories than absolutely necessary. Also reminds me of when my wife and I lived in Florida for six years. Our second-floor condo looked out over what Floridians call lakes - they are really water overflow retention ponds. Marines take the high ground for good reason, but beyond that, it is nice to observe alligators while one is not actually at ground level. Anyhow, there were sand hill cranes and other cranes and egrets, which would sit near the intake/outflow culvert, not more than eight or ten feet from an alligator that regularly would be sunning itself - or whatever it is that alligators do. While these shore birds seemed relatively relaxed with the gator nearby, it seems clear to me that they knew exactly what signs meant that the gator was on the move and that it would behoove them to seek safety in higher ground and elsewhere. Nature knows...
Fri, 01/31/2014 2:27am
David, your are right. I saw that video clip, awesome information and thank you !
Tue, 01/21/2014 8:39pm
For work on extremely high voltage lines, the linesman needs to wear a suit of chain mail. Otherwise, even the atmospheric electrical field is too great for safety. IEEE Spectrum ran an article on this, but this tells the tale:
Doesn't seem like at all a good idea.
Sun, 07/23/2017 12:22am
For what it's worth, I understand that sitting in an automobile during a lightning storm - presuming that one takes care to minimize touching any metal - is relatively safe, not because of the rubber in the tires serving as an insulator (apparently, I understand that insulation is not nearly enough to insulate a car, given lightning's power, never mind the steel belts in tires these days), but more because the metal skin of the car is essentially a Faraday cage. In sailboats at sea or at a mooring in a lightning storm, I have heard sailors say that they went below for the duration of the storm, but before they did, they attached metal chains to the stays - the guy wires that support the mast(s) - in contact with the chain plates, the fittings that provide the foundation support in the hull for the mast/running rigging stays - and then put the other ends of each of the chains over the side. I think that I understand, as well - though I'm less certain of this - that most, at least for more boats of relatively recent vintage/provenance, that sailboats' masts are grounded through to the keel. Perhaps someone with more than my limited knowledge might care to comment. I did used to belong to a small boat/yacht club in Ipswich Bay on the North Shore of Massachusetts for a number of years. The clubhouse sits atop a prominent hill and watching, from the clubhouse porch, lightning storms charge down Plum Island Sound was a favorite pastime for the members, once they were, of course, off the water. One time - and although I was on the club porch watching the storm - I didn't witness this phenomenon - I understand, from members who were inside the clubhouse, that what is apparently known as 'ball lightning' came down the clubhouse chimney and was, sort of, banging and sparking around the fireplace for a few moments. Apparently, it was quite the show, though I'm not sure how long it lasted - I imagine it would be pretty brief - the lightning, I think, 'knows' the quickest route to ground and finds it pretty instantaneously, I understand. Cheers!
Thu, 01/16/2014 8:43am
Above picture is look like birds sitting in Pixar - For the Birds (animated short film). Informative article, thank you Kate.
Thu, 09/21/2017 1:32pm
Bird is one of a large group of animals that lay eggs and have feathers and wings.It also has d capacity to stay on an Electric pole without been shock.But in some of the area in scientific conjuction it is said that bird usually shock but I'm not clear with that statement.
Sun, 07/23/2017 12:31am
Reminds me of when I was growing up, starting in the 1950's, and - before the widespread use of circuit breakers - we would occasionally overload an electrical circuit, resulting in a blown fuse. I had an uncle who had been in the US Army Signal Corps - telephone lines and such - in WWII who used to tell me to change the fuse with one hand and keep the other hand behind my back. Apparently, even if I were somehow careless or, otherwise, through 'pilot error' to experience a shock (although I was pretty darned certain not to let that happen; still, 'accidents' - more like carelessness - do happen), I understood, if were lucky, that the current might knock me on my hind end, but completing the circuit with the hand that was otherwise behind my back would, for sure, likely be the last time I made that mistake. I have a good deal of respect for things, like electricity, propane and other things that can kill you - and there seem to be more of those things in the world than not.
Sat, 07/22/2017 11:59pm
I recall this question being asked on a National Merit Scholars test way back in, oh, I dunno, maybe 1967 or thereabouts. Might have been a bit earlier - perhaps 1964 0r so, when I encountered the question and might have been a bit of in-class test prep. It's a doozie of a question. There were no test prep centers, books and all of the rest in those days. Plus, the first Sputnik went up in the autumn of 1957. Nothing like embracing yer geezer-hood. After Sputnik 1, the US government scrambled with technology and, especially defense grants and offered some of the first student loans, the National Defense Student Loan - NDSL program. I recall wracking my brain trying to solve this question. Don't know that anyone that I knew figured out what the answer was likely to be - and here the question surfaces some 50+ years later. Cool...