Birds often perch on high-voltage power lines, seemingly unaffected by the powerful electrical currents. This raises a common question: why are they not electrocuted? The answer lies in fundamental principles of electricity and the specific conditions under which it becomes dangerous.
The Basics of Electricity
Electricity involves the movement of electric charge, typically electrons, through a conductive material. This flow of charge is known as electric current, measured in amperes. For current to flow, there must be a driving force, referred to as voltage or electrical potential difference, measured in volts. Voltage represents the “pressure” that pushes these charged particles through a circuit.
A concept in electricity is the complete circuit. For electric current to flow, it requires an unbroken, closed loop of conductive material, allowing electrons to travel from a power source, through a conductor, and back. If this path is interrupted, current cannot flow. Electricity always follows all available paths, with more current flowing through paths that offer less resistance.
How Birds Avoid Electrocution
When a bird perches on a single power line, it does not complete an electrical circuit through its body. Both feet are on the same wire, meaning they are at the same electrical potential. With no significant voltage difference between its feet, virtually no current flows through the bird. The bird essentially becomes part of the wire, and electricity continues along the wire, which offers a far lower resistance path than the bird’s body.
The wire conducts electricity efficiently, making it the preferred route. A minuscule current might pass through the bird due to slight potential differences, but this is typically in the microampere range, too small to cause harm. For comparison, humans can feel a painful shock from about 10 milliamperes, and electrocution is possible around 50 milliamperes. As long as the bird only touches a single power line, it remains safe because it does not create a path for electricity to flow from a high to a low potential.
Situations Where Birds Are at Risk
While generally safe on a single line, birds can be electrocuted under specific conditions. A common scenario occurs if a bird simultaneously touches two different power lines that are at different electrical potentials. This action creates a complete circuit through the bird’s body, allowing a fatal current to flow.
Similarly, if a bird touches a live wire and a grounded object, such as a utility pole, a transformer, or the ground itself, it also completes a circuit, causing electricity to pass through its body to the ground. Larger birds, particularly those with wide wingspans like eagles or storks, face a greater risk. Their size increases the likelihood of inadvertently bridging the gap between two wires or between a wire and a grounded component when landing, taking off, or stretching their wings. Utility companies often implement measures, such as installing insulating devices or increasing spacing between wires, to mitigate these risks for wildlife.