Why do birds sit together on telephone lines?
For a start, most telephone wires are insulated and carry little
or no electricity so, apart from falling off and hurting
themselves, they won't get hurt on telephone wires. Really, you
should have asked about why birds don't get hurt on overhead
electrical wires. The answer is fairly simple really - to get
electrocuted from those wires you need to complete the circuit, in
this case touch the ground, for the electricity to surge through
the body. Birds only sit on the wire and do not touch the ground,
so they can't be electrocuted.