Study finds island goshawk population unique and at risk

When Canadian ornithologist Percy Algernon Taverner examined the goshawks of Haida Gwaii in 1940, he noticed something unusual about them. The birds on these rugged islands, about 70 kilometers off the coast of British Columbia, were slightly darker than the northern goshawks nesting on the mainland.

He designated them a subspecies, Accipiter gentilis laingi, distinct from most of the other goshawks (Accipiter gentilis atricapillus) distributed across the continent.

Recently, biologists found, differences run deep between the Haida Gwaii goshawks and others — separated by perhaps 20,000 years of evolution. The last remnant of these distinct goshawks numbers only about 50. Surveys on Haida Gwaii have indicated the population is declining and at risk of extinction.

“We don’t want to lose them,” said Darren Irwin, a University of British Columbia professor and senior author of a genomic study of the birds published in Evolutionary Applications. “It appears they’ve become adapted to the environment of Haida Gwaii and they’re a key part of the ecosystem.”

Their findings, however, could create some wrinkles in conservation efforts. The subspecies, A. g. laingi, is presently considered to include all the goshawks throughout British Columbia’s Pacific Coast. The Canadian governments lists these birds, numbering about 1,200, as threatened.

But Irwin’s team, led by UBC researchers Kenneth Askelson and Armando Geraldes, found the Haida Gwaii population was distinct from all these other goshawks, raising questions about what that means for the designation of the subspecies.

“It will be interesting to see what the authorities decide to do,” Irwin said. “To us, what we’re doing is making these genomic patterns known. It’s not quite up to us to redefine the subspecies.”

Regardless of what it means for the scientific classification, the researchers say their findings demonstrate that the birds of Haida Gwaii represent a unique population that is small and getting smaller, with “a high risk of extinction of an ecologically and genetically distinct form of northern goshawk.”

The goshawks long occupied the dense, old growth of the islands’ rainforest, which gave them ample cover to quickly descend on prey, Irwin said, but with deforestation, their numbers have declined, along with goshawks across the continent. Conflict with humans, including getting entangled in fences protecting chicken coops, has also affected their numbers.

To sustain the population, Irwin said, “protect the forest. That’s the number one thing.”

Header Image: Since 1940, biologists have recognized the goshawks on the islands of Haida Gwaii were distinct from other northern goshawks. ©Berry Wijdeven