The bird, its poo and the huge power outage that hit Northland

Birds, their nest material and their poo can trip circuits, causing power circuits to trip and disconnect. Photo / Supplied

Perched high up in a power pylon, a heron peers across the Kaipara under a brilliant blue sky.

The bird launches into flight, relaxing into the air and letting loose a stream of poo that splatters across a pylon.

On this occasion, says Transpower, it believes it's likely the stream of poo formed a bridge for electricity creating a "flashover" effect.

This is the scenario Transpower has described to explain the three-hour power outage that affected 92,000 homes and businesses across Northland on Wednesday.

The detail emerged when the Advocate told Transpower of scepticism among bird lovers over its "bird poo" explanation.

Readers were doubtful. One, who studied ornithology at university, spoke of being "a bird watcher for decades", mainly around the Kaipara, and "large water birds don't congregate or perch on towers or pylons".

A heron perched on a pylon. Photo / Supplied

There were thousands of large water birds on the Kaipara and its shores - "never seen any of those on power towers or pylons".

When it comes to the poo story, she urged us to "dig a little deeper".

As it happens, Transpower had the evidence. Photographs of birds standing on pylons, nesting on pylons and flying away from pylons appeared to provide evidence of a connection between birds and pylons.

A Transpower spokesman said: "Bird excrement, wing span and even material carried by birds, can enable flashovers by providing a path across the insulation that separates the wires from the steel towers.

Away with the birds, taking over power pylons. Photo / Supplied

"This is extremely common and a challenge we face across the country."

A flashover, he explained, was an arc of electricity passing from the wires to the steel towers through a conductor that was not anticipated.

"One likely cause is the bird emptying its bowels upon taking flight from perching on the tower, letting loose a long jet of droppings on to the insulator.

The piece of equipment believed to have been hit by bird poo, taking out Northland's power. Photo / Supplied

"There is evidence of this 'bird streaming' seen on the affected tower in question."

Transpower's spokesman said the power outage didn't actually require repairs or equipment replacement. The company made live again the circuit that had tripped and it has worked since without fault.