Barn owls struggling to adapt to urban sprawl

One of Canada’s largest populations of barn owls may be more aptly named bridge or overpass owls because they’re losing normal roosting spaces and struggling to adapt to urbanization, a new study says.

It was based on owls around Metro Vancouver and found that habitat loss, road deaths and rodent poison have a lethal impact on the birds but changes to green-space policies and public education could mitigate the loss.

Wildlife biologist and lead researcher Sofi Hindmarch said the original focus of the study was on the impact of rodenticide, but that changed when the owls were seen to be dependant on hunting along grass growing next to highways.

Barn owls’ hunting behaviour usually involves flying within a metre of the ground, making them especially vulnerable to being hit by vehicles, said the study contracted by Environment Canada and published in the journal Landscape and Urban Planning.

Most of Canada’s barn owl population is found in British Columbia’s Lower Mainland and the Fraser Valley, said the study about the bird that is recognized for its distinctive tan-coloured, heart-shaped facial disk.

The research was conducted between 2010 and 2014, when 11 adult barn owls were radio tagged and followed for five to 12 months, until the transmitter fell off or the battery died.

It didn’t take long for researchers to learn that the owls faced certain dangers in urban settings.

“One female was reported dead two weeks after being radio tagged, likely the victim of a vehicle collision,” the report said. Road mortality is recognized as one of the main threats to the owl population in both Europe and North America.

Hindmarch tracked the birds at night and said she was surprised about their urban wanderings.

She followed one pair to an industrial building, other birds to overpasses and another pair to a busy commuter bridge over the Fraser River.

“A lot of these areas were predominately grass, marsh and farmland not that long ago. I suspect these are kind of remnant individual populations that are still persisting in an environment that is becoming increasingly urban.”

In the Lower Mainland and Fraser Valley, where blueberries and greenhouse-grown vegetables are the region’s fastest-growing crops, the birds’ grassland habitats are disappearing.

High-density human developments and farming also draw rats and mice, which the study said prompt the need for rodent control.

Hindmarch said researchers began the field study to determine if the owls were being exposed to poison as stricter regulations were being implemented.

Barn owls were more likely to eat prey exposed to poison if they were hunting in grass growing along the roadside, while that possibility decreased for owls with a home range of hayfields or other grass habitat, the study said.

“Threats from the loss of habitat and nest sites were the main reasons barn owls were recommended to be upgraded in 2014 to ‘threatened’ in Western Canada,” it said.

The Canadian Species at Risk Act lists the Western barn owl population as a special concern, while the Eastern population found in southern Ontario is listed as endangered.

But Hindmarch said the owls she studied were highly adaptive and could coexist with humans.

“We just have to be willing to share a little bit of our real expensive land mass with them.”

Some cities are already creating wildlife corridors, considering alternative nesting sites, and leaving grass areas in their parks wild to accommodate wildlife habitat, she said.

“That doesn’t only benefit the barn owls, our bees are in decline,” Hindmarch said. “There are so many other species that would benefit in making sure we have wild flowers and grass, not just golf-course grass in our parks.”