Climate Change and Housing Adaptation: Owl Edition

After scores of barn owls died in overheated nest boxes, conservationists set out to give the birds less heat-prone homes

In British Columbia, barn owls fledge in mid-summer, much later in the year than owls farther south. The regional adaptation meant many juvenile birds were still too young to fly when a deadly heat dome cooked the province in June 2021. đź“· Mark Caunt/Shutterstock

This story was first published in Hakai Magazine. You can find the original here.

For several scorching days in June 2021, an oppressive heat dome sat over western North America. In the Fraser Valley, inland from Vancouver, British Columbia, the temperature soared to 42.9 °C. The previous June high for the area—set in 1982—was 34.7 °C. Unable to escape the extraordinary heat, billions of marine creatures died—most noticeably barnacles, mussels, oysters, and clams.

On land, Sofi Hindmarch, a wildlife biologist with the Fraser Valley Conservancy, tallied the heat dome’s horrifying impact on young owls.

At nine locations across the Fraser Valley, Hindmarch, biologist Dick Clegg, and farmers documented juvenile barn owls that had fled their nest boxes. Like people bolting from an apartment fire, the owlets jumped to escape the overwhelming heat. At seven of those sites, the researchers found corpses strewn on the ground below the nest boxes. These owlets were too young to fly, and their parents did not feed them on the ground. From the eighth location, Hindmarch collected three fallen but uninjured young owls and took them to a rehabilitation facility; they survived and were eventually released. In the ninth case, two young owls that fell from a nest box in a barn managed to land in hay, where their parents continued to feed them until they were old enough to fledge—typically around 60 to 70 days old.

Along with these grisly findings, the study authors documented 28 dead barn owl babies, aged 20 to 45 days, inside their nest boxes. “For me, it's extremely rare to find a batch that is almost ready to fledge all dead,” Hindmarch says.

When she began studying the region’s barn owls more than two decades ago, extreme heat was the last thing on her mind. Barn owls originated in the tropics, and the Fraser Valley sits within the species’ uppermost limit in North America, Hindmarch says. “I honestly never envisioned that overheating would be an issue for them,” she says. “It came as a bit of a surprise. We never used to get temperatures like we do now.”

While the changing climate and soaring heat are at the heart of this tragedy, part of the problem stems from the very nest boxes the owlets were abandoning.

Built out of plywood and erected on freestanding poles or affixed to the sides of barns, many nest boxes were exposed to direct sunlight, exacerbating the skyrocketing temperature outside. Hindmarch and her colleague later found that owlets living in pole boxes within 350 meters of the coast, however, survived. At the outlet of the Fraser River, where it dumps into the cooler Strait of Georgia, the 2021 heat dome temperature peaked at 32.4 °C—more than 10 °C cooler than at sites farther inland.

Nest boxes have long been used to give birds a helping hand, but for Hindmarch, the disaster showed it was time to reconsider their design and placement.

To that end, Hindmarch and volunteers with the Cascade Bird Box Team have retrofitted about 30 nest boxes in the Fraser Valley study area since the heat dome. They made some of the boxes larger and added ventilation holes. They repositioned other boxes so they’re out of direct afternoon and evening sun. And for the boxes most exposed to sunlight, volunteers covered the old roofs with white sheet metal to reflect the heat, leaving a gap between the two surfaces to improve air circulation. Together, these modifications have lowered the peak daytime summer temperatures inside the boxes by about 5 °C.

But improving nest-box design is only part of the solution, says Katherine Lauck, a graduate student in ecology at the University of California, Davis, who was not involved in the barn owl work. Lauck recently coauthored a study showing how birds—much like people seeking the coolness of forests on a hot day—need natural spaces to cope with climate change–induced heatwaves.

Species such as western bluebirds and tree swallows, Lauck found, fare better when nesting in boxes near shady forests, which act as a buffer from heatwaves. Boxes on open farmland are more susceptible to extreme swings in temperature.

Human-dominated landscapes, such as farms, says Lauck, also restrict the birds’ access to water and food, making them even more sensitive to temperature extremes. One way to improve birds’ odds of success in a warming world, Lauck says, is to add shade to agricultural land. “Patches of natural vegetation interspersed with crops are going to be really important to allow birds to cope,” Lauck says.

Hindmarch agrees that updating nest boxes is just one step toward solving this complex problem. Barn owls are adaptable creatures that live on all the world’s continents except Antarctica. Protecting mature trees and dead snags—which offer nesting cavities for barn owls—as well as areas such as wetlands and natural grasslands will go a long way to improving the species’ chances of enduring the juggernaut that is climate change.

This story first shared in the June 5 edition of the Fraser Valley Current newsletter. Subscribe for free to get Fraser Valley news in your email every weekday morning.

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