Cedar waxwing chicks.

Bird Nesting: Study looks at impact of BC Hydro operations on birds that nest in drawdown zone

Study looks at impact of BC Hydro operations on birds that nest in drawdown zone



I don’t think I’m cut out for birding.

I was out once again with Harry van Oort, the ornithologist leading a study of nesting birds in the draw down zone of the Columbia River around Revelstoke. He was showing BC Hydro’s Jen Walker-Larsen and myself the nest of a chipping sparrow on the flats at 9 Mile south of Revelstoke

His instructions were fairly simple – walk by slowly, don’t get too close, try not scare away the bird and do a quick check on the nest.

“We don’t all three go blundering up, look at it, scare her away, take photos and leave,” he told us.

He walked up towards a willow tree where the nest was located. He stood by and pointed to where the nest was and then directed me to come up. I walked up slowly but my eyes were unable to spot the well concealed nest. I poked in closer until I could finally spot the small songbird before it flew off, leaving its bright blue eggs wide open for predators.

I snapped a few pictures and then we walked away from the nest to give the sparrow some room to fly back.

Most nest failures in the drawdown zone are due to predators, van Oort told me. “The reservoir is by far a smaller cause of nest mortality,” he said.

The bird nesting study was launched in 2008 as part of the Columbia River Water Use Plan. The purpose is to look at the impact of reservoir operations on nests in the drawdown zone.

The area is a popular bird nesting site. In 2010 surveyors found 400 nests from 37 bird species, according to a CWUP update released by BC Hydro in April. Of the nests that failed, nearly half failed due to predators while 11 per cent failed due to reservoir flooding.

“The reservoir is by far a smaller cause of nest mortality,” said van Oort.

In 2009, 43.4 per cent of 212 nests were successful and seven nests failed because of reservoir operations. One of those nests was that of an American Avocet, which is red-listed as an endangered species.

Our initial plan was to meet at Centennial Park and go for a tour around there but instead we drove down to 9 Mile. On the way there we passed the Montana Slough, where Airport Way makes the big bend south of the airport; Van Oort excitedly asked us to stop.

The slough, he explained, was essentially a floating island – a unique feature in the reservoir. It would rise with the water to an elevation of about 438.5 metres – close to maximum water levels.

During the 2010 study, he said, they discovered that as other nesting areas got flooded birds would flock to Montana Slough to rebuild their nests.

“Even territorial songbirds will move their nests there if they get flooded out,” he said. “It makes the whole story a lot more complicated. It’s nothing anyone would have guessed.”

Next, we drove past Cartier Bay – one of the lowest elevation wetlands in the Revelstoke Reach. “There’s not a lot of great nesting habitat there,” van Oort said.

We reached 9 Mile and parked to the side of a dirt road along the flats. After asking van Oort a few questions about the work, we headed off through thick sedge and canary grass in an area that was staked with cottonwood plants last spring.

Van Oort and his team colleagues at Cooper, Beachesne and Associates, the consulting firm conducting the study, staked out several plots in the area to look for bird nests. The plots differ in terms of their elevation and vegetation and from there they extrapolate numbers for the entire Revelstoke Reach drawdown zone.

Locating the nests is another challenge. While we stood by the car, van Oort picked out the call of a yellow warbler.

“I can tell you right now there’s one yellow warbler singing right there,” he said. We assume he’s got a female, we assume they’re nesting, we find it.”

For other species, like ducks, they will take a string, line it with something noisy and drag it through the area, scaring up the birds.

“You have a whole quiver of tricks to find out what’s out there,” he said, adding that they do sometimes miss some. They also don’t look for nests more than 3 metres off the ground, both because they’re harder to detect and they aren’t impacted as much by the reservoir.

When a nest is found a marker is placed about 10 metres away. A second, smaller marker is placed closer to the nest so the person will know where to look. That minimizes the amount of time spent trampling around the nest looking for it. All nests sites are marked on a GPS and they’re visited every three days

We were at a fairly high elevation where some birds choose as their second sites when their first nests get flooded out by the reservoir. When the water level rises and floods out the nest, the birds will start over again elsewhere. Savannah sparrows, van Oort said, were one of the species to move their nests to this area. They hadn’t yet though.

The biggest cause of nest mortality is predators – notably snakes, small mammals, crows and ravens.

The ornithologists doing the study conduct surveys at numerous locations in the Revelstoke Reach, including Downie Marsh near Centennial Park, Montana Slough, Machete Island, 9 Mile and spots further south. Some areas are much more popular than others.

As the case with all the ongoing studies surrounding the Columbia River Water Use Plan, no conclusions are being made yet. A map showing nest density throughout the reservoir will be made and a report will be made on where and when birds nest.

“Then we figure out how to optimize reservoir operations to minimize impacts,” said van Oort. “Someone’s going to have the tough job to figure it all out.”

On our way back to the car we had a nice surprise when van Oort identified the squeaking of a vole nearby. We peered our eyes downward to get a look when I spotted a snake – a Thamnophis elegans (western terrestial garter snake in English), van Oort said. The snake was trying to get at a vole that was hiding in the grass.

Van Oort bent down and started spreading apart the thick grass. Suddenly the vole jumped out and scampered away, out of the clutches of the snake.

And, for the record, van Oort informed me last Friday that the nest I disturbed was still there and doing well.