More about birds and powerlines. I have read all the discussions about how safe it is for a bird to stand on a high voltage power line. Ok. But my doubt is not about what happens when the bird is standing, but about what happens when it touches the ground, or a tree, after standing on a power line. We have all seen that when workers approach (with helicopters) high voltage lines, they have a metal stick that they use to put themselves and the helicopter at the same potential as the line, but not too fast as they would do if they touched the wire directly with their hands. They also wear a protection uniform in order to make the charge flow around their bodies and not through it. That means acquiring charge. Then when they approach the ground they have to use the same stick to discharge before touching the ground themselves, for the same reason. It seems birds do not have to worry about this. Is it because they acquire a small charge even in high voltage lines?? 
 A: Treated as a sphere of radius 4 cm, a medium-sized bird has a capacitance of about 4 pF. Perched on a power line at a potential of 400 kV, the bird will acquire this potential, and (using $Q=CV$) a charge of about 1.6 $\mu$C. 
The bird then flies off. My guess is that she will lose most of the charge in flight. That's because the air will be very slightly conducting, owing to odd ions and, possibly, to chain-forming by (polar) water molecules. Since the bird's capacitance is so low, even a very high air resistance (say $10^{12}\ \Omega$) will produce a low time constant, maybe in the order of a second. 
Suppose, though, that the bird retains all charge (and therefore potential) when it lands on the ground. Let's now add legs of combined resistance 1 k$\Omega$ to the spherical bird. The initial current (using I = V/R) will be 400 A. Surely that will kill the poor thing? I'd guess not, because significant current will last (using $T=10RC$) only in the order of 40 ns, and the energy dissipated in the bird's legs will (using $E=\frac{1}{2}CV^2$) will be only about 0.3 J. There are, of course, more subtle physiological effects than sheer heating effect, so this argument doesn't pretend to be conclusive.    
