[hamza (OP)]

I know there must be lots of explanations around but i can't get it that why birds don't get electrocuted when sitting on the power lines of the electric posts??

[techmind]

To get an electric shock, you need a current to flow through your body (and to be electrocuted, that current has to flow near the heart). For a current to flow, you need two electrical connections - and "in" and an "out", if you like. Since a bird only sits on one wire, and in free space, it feels little effect from the electricity since there is no complete circuit.

As humans we have to be careful however with mains electricity, as touching a single live electric wire can prove very harmful (though there are some circumstances when it won't). The problem is that often the "second" electrical connection is present but not obvious. This may be something metal (and earthed/grounded) that the other hand is touching, or merely resistance and capacitance from the body -typically through the feet- to ground. At AC, a current can still flow "through" a capacitor!

There are some procedures where engineers inspect live 400kV overhead transmission lines from a cradle hanging off the wire... again they can do this because they're only in contact with one wire. But they do have to be very carefully lowered onto the wire by helicopter.

See some nice photos at:
http://www.chopperworx.co.za/powerline.html

and look about half way down this page:
http://www.helicoptersotago.co.nz/commercial_ops.html

[hamza (OP)]

Thanks techmind for the elaborated explanation.. It really worked..

[neilep]

Is it not also that the electricity just can't be bothered to go up birdies feet as it's far more efficient to carry on down the wire...as the electricity will always take the shortest route ?...and a trip up birdies legs is a detour !

[iko]

These 'birds' have to watch out for wires and power lines...

http://upload.wikimedia.org/wikipedia/commons/thumb/3/37/Zenon.jpg/450px-Zenon.jpg

[paul.fr]

I think we have had this question a few times.
here is one http://www.thenakedscientists.com/forum/index.php?topic=350.msg115237#msg115237

[RD]

I know there must be lots of explanations around but i can't get it that why birds don't get electrocuted when sitting on the power lines of the electric posts??

Large birds can get electrocuted when perching on the pylon/post: their large wingspan is sufficient to touch the live cable whilst perching on the earthed post/pylon.

http://www.naplesnews.com/news/2007/mar/27/fpl_looking_whether_hurried_repairs_after_wilma_ar/

[electrocutionexpert]

An MIT student answered it like this: "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.”

As other readers have pointed out, "if the bird stretches out a wing or leg, and touches the second wire, it can open a path for the electrons to electrocute the bird." This is similar to what happens with humans- we often touch both the ground & a wire, so the electrons have motivation to travel through us (electrocution). 

This is the most simplistic explanation I've found: electrocuted.com/2016/02/26/birds-power-lines/

[chris]

This is summarised in the Naked Science Scrapbook on why birds can sit safely on power lines that we made a few years ago.

[alancalverd]

As an aside

www.standard.co.uk/newsheadlines/horses-electrocuted-at-racecourse-6566545.html

To summarise: a broken and abandoned underground electrical cable produced a large potential difference over a couple of meters. This posed no problem to a human as his feet would be in dry shoes and only a few centimeters apart, but over the "wheelbase" of a horse the voltage was lethal and conducted into the animal via aluminum racing shoes..