How genetically unique is the coastal northern goshawk?
A new gene-sequencing study funded by the province, the Coast Forest Products Association and Genome BC will try to answer that question.
First identified on Haida Gwaii in 1940, coastal goshawks are raven-sized hawks that evolved to hunt under the canopy of old and mature coastal rainforests.
Logging has reduced their habitat, and on Haida Gwaii, introduced deer are also eating their prey out of house and home.
Estimates suggest there are only about 1,000 coastal goshawks left in B.C. — over half the global population — with about 400 on Vancouver Island and just 50 or so on Haida Gwaii.
Since 2000, the B.C. and federal governments have listed the coastal northern goshawk as a threatened subspecies (Accipiter gentilis laingi), but there is some debate about how distinct they are from their more common cousins in the interior (Accipiter gentilis atricapillus).
Researchers hope the gene-sequencing study will help resolve the issue.
“We know that goshawks have adapted to different coastal environments,” says Steve Gordon, manager of B.C.’s conservation and biodiversity program.
“This will tell us whether that’s just a local adaptation — what’s known as an ‘eco-type’ — or an actual subspecies.”
Dr. Dennis Irwin is a zoologist at the University of British Columbia who is leading the 18-month study, which will compare the DNA of coastal and interior goshawks.
“However laingi is defined, whatever range it has, it’s got a pretty small population size,” said Dr. Irwin.
“When populations get that small, you really worry about any kind of disease or severe event causing extinction.”
Irwin and his colleagues are now gathering existing samples from goshawks found on Haida Gwaii, Vancouver Island, and other parts of the B.C. and US coast.
Not only is it a challenge for people to distinguish coastal and interior goshawks by looking at them — coastal goshawks are smaller and darker — Irwin said even previous genetic studies have failed to find significant differences.
But Irwin said the methods those studies relied on could only look at a tiny part of the bird’s genetic make-up.
“Other parts of the genome might show more clear difference between the Haida Gwaii population and elsewhere, or between all of coastal B.C. and elsewhere,” he said.
Whereas one earlier study sequenced just 10 base pairs of DNA, using a new method called genetic bi-sequencing, Irwin and his colleagues can sequence something on the order of 10 million.
That is still less than half a per cent of the 1.3 billion base pairs found in a typical bird genome, but it should be enough to see where some of the differences lie between coastal and interior goshawks.
Measuring the genetic variability in the goshawks’ genome could also give researchers an idea of their historical population size — something that has already been done with endangered mammals.
“They can use the variation in there to say, ‘Well, right now the population is down to 100 individuals, but we infer from all the variation that it used to be a million,’” said Irwin.
Steve Gordon said the genome study is one of several recent projects will help the province finish a final recovery plan for northern goshawks, which is expected by 2020.
Required under the federal Species at Risk Act, the plan is likely to have a significant impact on forestry companies.
Last winter, provincial officials visited Haida Gwaii to discuss the plan with the Haida Gwaii Management Council, local forest companies, biologists, and NGOs.
“Haida Gwaii is really considered the core of the coastal goshawk habitat,” said Gordon.
A few years ago, B.C.’s forestry industry balked at the protections laid out in a draft federal plan.
Unlike the B.C plan, at this stage the federal one does not consider any socioeconomic factors.
“The forest sector was quite critical of the federal government’s approach,” said Gordon.
“We don’t currently know what the final content of that recovery strategy will be.”
So far, Haida Gwaii is the only place in B.C. with a land-use order that requires a 200-hectare protection zone around all known goshawk nests.
There are currently 19 known nests, and while all 16 that researchers looked at in the last field season were inactive, the discovery of one injured and two dead juvenile goshawks this year indicates there are successful nests elsewhere.
On Vancouver Island and parts of the coast, companies have more discretion based on local features, but a buffer of at least 176 hectares is considered low-risk.
More challenging is the question of how to preserve the coastal goshawk’s foraging habitat — they need thousands of hectares for hunting, and 40 to 60 per cent of it must be old-growth, or mature second-growth forest.
“Managing foraging habitat is quite complex,” said Gordon.
For example, goshawks can breed and hunt in mature second-growth, but as it becomes suitable habitat for goshawks, it also becomes suitable for forestry.
“So we need to look at rotation ages and the sequential development of the forest,” he said.
“How much do we get by default, in terms of maintaining some forage habitat?”
Asked how the public can be assured the genome study is sound science given that it is partly funded by the forest industry, which has an interest in limiting habitat reserves, Gordon said all the work is done at arm’s length, through Irwin’s lab at UBC.
“That’s the fundamental reason for having a university conduct this research,” he said. “It’s an accredited academic institution which is completely arm’s length and independent.
“It is pure science, and the results will be published in scientific journals that require anonymous peer review.”