WAEC - Physics (1990 - No. 46)
Birds can perch safely on overhead electric power cables without being electrocuted because
birds can withstand high p.d. of the electric power cables
any accumulated charge on the birds is quickly dissipated
the feet of the birds are well insulated
the current is a.c. and has particular direction
there is no p.d between the birds and the cables
Paliwanag
A bird remains safe on a single wire because it has only one point of contact, keeping it at a single electrical potential. However, if the bird touches another object with a different potential, it would complete a path to the ground, resulting in severe electric shock or electrocution.