ACHO DENE KOE/FORT LIARD - A research project is showing that one bird species around Fort Liard tends to avoid corridors of land cleared for oil and gas exploration - known as seismic lines - which can result in a lower number of birds in an area.

Ovenbirds are a type of warbler, a small songbird, with a long migration route.

A research project is examining how male ovenbirds around Fort Liard interact with seismic lines and why. - photo courtesy of James Campbell

The birds, which can be found across most of Canada and the United States, establish a territory, raise a brood and then fly as far as South America for the winter before returning to the same territory the next year, said Hedwig Lankau.

"They're a pretty amazing bird," said Lankau, who is completing a master's degree in ecology at the University of Alberta.

Lankau and a team of three field assistants have spent the last two and a half months studying how male ovenbirds who reach Fort Liard interact with seismic lines in various stages of regrowth.

"They're sensitive to the lines," she said.

Male ovenbirds defend their territory and attract mates by singing. The males usually won't put their territory across a seismic line so if there are enough lines in an area it reduces the number of birds found there, said Lankau.

The research project is trying to determine how long it takes a seismic line to regrow to a point where it doesn't affect the birds.

"We don't know when the lines reach that point," the graduate student said.

Lankau is looking at three line types: one that is open with no shrubs, one in a medium stage of regrowth with some shrubs but no small trees, and one that is overgrown and can be hard to distinguish from the surrounding forest.

While looking at about 12 lines in her pilot season last year Lankau found that as the lines regrow, the birds are less likely to be affected. The height of the plants can be used to gauge how the overbirds will interact with the line.

Starting in mid-May the team looked at another 15 lines this year over a large area ranging from 100 km north of Fort Liard to 60 km south of the hamlet and into northern B.C.

The team only had about four weeks starting in June to find the male ovenbirds, which only sing for about five hours beginning at sunrise.

"You have a small window of time in the day to find the males," Lankau said.

A researcher would follow the bird around at a distance and flag all the areas in which it sang to mark the extent of its territory, noting if it crossed a seismic line.

Each bird, of which there were more than 55 in the two seasons, had to be tracked two to three times to get enough data.

Having confirmed that the birds avoid seismic lines, Lankau is now seeking to find out why. Ovenbirds are ground foragers and there may be less food on the lines, so they don't want to include them in their territory, she said.

Another theory is that the birds use the lines as landmarks to mark the boundary of their territory.

With the birds quiet for the year, the team is now surveying the vegetation on the study's seismic lines and looking at the leaf litter where insects, the birds' food source, live.

The research will help to develop ways to minimize the effects of seismic lines, said Lankau. Measures could include not removing the leaf litter or assisting the line to regrow faster, she said.