WATERLOO REGION - When the clocks on your electronic devices are flashing, you know two things - the electricity supply was disrupted and, depending on where you live, you can probably blame squirrels.

The small animals are responsible for up to two-thirds of the power outages at some utilities.

Wendy Hearn knows all about it.

She lives on Arnold Street, an older neighbourhood in Kitchener with lots of big trees and exposed overhead wires. That is exactly the combination that leads to a lot of power interruptions caused by squirrels that love to run, jump and live among trees - and scamper along the wires.

"On Arnold Street, I am telling you, we lose power so often," Hearn says. "The power is always an issue."

Digital clocks on the microwave and stove must be reset at least three times a week in Hearn's house. At least three power outages lasting four hours or longer have hit Arnold Street since Hearn moved there in June. The power supply always seems tentative.

"It flickers all the time," Hearn says.

While squirrels are responsible for most of the power outages caused by animals, raccoons and birds are also to blame.

Chris Derry lives on St. Vincent Street, not far from Hearn's house, and his electricity supply is constantly interrupted.

"This is not an exaggeration - the power goes out every day in our house," Derry says. "I know we had a bird fry a power box once."

That bird caused a blackout that lasted for two days. Derry heard a loud bang. When he went out to investigate, Derry found a bunch of feathers and a burned-out transformer.

"We can't set digital clocks," Derry says. "We don't even bother setting the clocks on the stove or microwave anymore."

Derry uses a lot of power bars.

"I have surge protectors on everything, otherwise my stuff is going to blow up," Derry says.

Most of the time, the power outages last a couple of seconds. If not for flashing clocks or flickering lights, you would not even know. But an alarm clock losing the time can make someone late for work.

For electrical utilities, the issue is much more serious.

The costs add up when trucks are sent out to patrol a line and determine the cause of the outage. This happens for every power failure. The utility wants to know if the cause is something that can be fixed right away - such as a tree branch lying across two wires. That costs money.

Many times all they find are scorch marks on the transformers and a dead squirrel on the ground. When Kitchener-Wilmot Hydro finds a place where squirrels caused more than two power failures, special equipment is installed on the wires and transformers. That also costs money.

Sometimes the transformer must be replaced, further increasing costs and prolonging the local blackout.

Cambridge North Dumfries Hydro appears to be leading the way in this region when it comes to preventing squirrels from causing power outages.

During the first nine months of this year, the Cambridge electrical utility had 125 outages. Squirrels were responsible for 13 outages or approximately 10 per cent. Birds, high winds, car accidents, tree limbs or unknown interference caused the rest.

Barbara Shortreed, spokesperson for Cambridge North Dumfries Hydro, says the utility has installed 2,500 to 3,000 wildlife-protection devices on the 3,500 pole-mounted transformers on its grid.

One of the hot spots is the Galt section of Cambridge which has lots of big trees, and that means lots of squirrels.

"These outages are expensive, so proactively we do monitor unplanned outages and target areas for wildlife-protection devices," Shortreed says.

When a squirrel short-circuits the power supply on a transformer pole, its charred body almost always falls to the ground, and the electricity supply automatically kicks back in. But if the squirrel's body gets stuck in place, the lights go out in at least a dozen homes. There is one pole-mounted transformer for every 12 houses.

The lights stay out until the squirrel remains are removed and the equipment repaired.

Electrical utilities closely track power outages. The frequency declines significantly during the winter months when squirrels are curled up in leafy nests.

"As soon as the weather turns nice, it is a big problem," says Jerry Van Ooteghem, president of Kitchener-Wilmot Hydro.

Last year, animals caused 150 power outages for the Kitchener utility.

"The vast majority are caused by a squirrel, that's for sure," Van Ooteghem says.

Put another way, 28.3 per cent of the customers hit by a power outage last year in Kitchener or Wilmot Township can blame squirrels.

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When building new power lines or rebuilding old ones, Kitchener Wilmot Hydro installs special equipment to prevent squirrels from short-circuiting the system. The wires leading into transformers are insulated, or the wires are spaced further apart so a squirrel cannot touch both at the same time, or tubes are placed on wires that spin when a squirrel tries to move on it. Others special equipment is installed to increase the distance between live wires and the top of transformers.

"So we have a program to do that, but it is very time-consuming and expensive," Van Ooteghem says.

"We basically replace the equipment at a transformer to increase the insulation distance from a live part to a grounded part so squirrels can't bridge that and cause a short circuit," Van Ooteghem says.

At about 150 locations in Kitchener, there are switches on top of poles that have what are called three-phase transformers. These units are usually along main streets. They supply power to entire neighbourhoods, and each one has a load-interrupter switch. When the power supply falters, the switch closes and power from another direction flows into the neighbourhood.

"They tend to be the ones most problematic because there is more equipment at the top of the poles, so there are more places for a squirrel to bypass and short out the equipment," Van Ooteghem says. "So we have been focusing on the three-phase transformers."

The utility installed special spiral-shaped devices to prevent squirrels from short-circuiting these switches.

"That is a lot more expensive to do, but these switches are expensive to maintain or replace if a squirrel shorts them out," Van Ooteghem says.

The utility spent $300,000 during the past two years to guard against squirrels.

During the first nine months of 2013, Kitchener-Wilmot Hydro recorded 65 power outages caused by animals. That will translate into about 100 for the entire year - down from 156 last year.

"So it's an improvement and I think this program is making a difference, but because it is expensive it will take a number of years for us to get around to doing a lot of the locations," Van Ooteghem says.

The suburbs are spared power outages caused by squirrels because there are few big trees to attract squirrels. Also, the power lines are underground in suburbs built since about 1970.

It would be way too expensive to put the power lines underground in old-urban neighbourhoods. As well, all of the houses in older areas are set up to receive electricity from overhead connections, not below ground.

The utility tried to trap squirrels and raccoons at some transformer stations, but the bait ended up attracting even more animals.

Squirrels love to chew because they are continually teething. An adult squirrel's teeth grow an average of 25 centimetres (10 inches) a year. Sometimes they chew into transformers and live wires, shorting-out the system.

John Janzen, the president of Waterloo North Hydro, says if customers notice lights flickering or digital clocks starting to flash, they should report it immediately.

"Because that will give us a better opportunity to diagnose it, patrol the area and find where the cause is," Janzen says. "If it is a branch causing it, we would want to get that branch trimmed. It's good to know where and when it is happening."

Animals are blamed for 25 per cent of the 321 momentary interruptions last year on the Waterloo North Hydro grid.

Janzen says the utility puts animal guarding on all new equipment and on old poles and transformers if a squirrel causes trouble there.

Waterloo North Hydro covers a huge area - 673 square kilometres - with long power lines stretching into Wellesley and Woolwich townships.

"If you live in the older part of the city where the power supply is overhead and there are lots of large trees and therefore squirrels and chipmunks and wildlife around, it can become a real nuisance," Janzen says.