Nature & Beasts
Why can a bird sit on a power line without being hurt?
- Both feet are at the same voltage
- Feathers insulate it
- Birds resist electricity
The answer is Both feet are at the same voltage. No difference between its feet, so no current flows through it.
Because current only flows where there is a difference in voltage, and both of the bird's feet are on the same wire, a few centimetres apart. There is almost no difference between them, so there is nothing to drive a current through the bird. The wire is at thousands of volts relative to the ground, but the bird is not touching the ground.
Touch a second wire, or a pylon, and it dies instantly - which is exactly why large birds are electrocuted on distribution poles and small ones are not. Wingspan is the risk factor, and utilities fit perches and insulate the gaps on eagle and stork routes specifically.
The same rule explains why line workers can work on live cables from a helicopter: they bond themselves to the conductor first, so they and the wire are at the same potential, and then everything they touch is at that potential too. It is also why a car is safe in a lightning strike - not the rubber tyres, which is the popular explanation and wrong, but the metal shell conducting the charge around the outside.