Ptarmigan, gyrfalcon numbers drop in Canada’s Yukon: study

Declining gyrfalcon and ptarmigan numbers may be due to climate change, says Yukon scientist Dave Mossop. (CBC)You might call it the canary in the coal mine: A Yukon biologist says ptarmigan and gyrfalcon populations could be in decline across Canada’s northwestern Yukon territory.

Dave Mossop says the fluctuations in these two “key” species could be a sign of greater trouble across the food chain.

Both populations usually peak in a 10-year cycle but recent bird surveys do not indicate a peak as expected. Mossop says the unexpected change in the cycle could be a result of climate change or other factors.

“For the last cycle yes, it declined, for reasons that we don’t understand,” says Mossop. “But the great hope is that things will re-establish themselves. The 10-year cycle in the boreal system is one of the most obvious things that’s happening, and for some reason it faltered. That’s kind of where we are now.”

Mossop says gyrfalcons depend on ptarmigan as a source of food and that the predatory birds will stop breeding when there aren’t enough ptarmigan to eat.

He says the Yukon Research Centre has access to a database on arctic birds which dates 50 years. Mossup says tracking willow ptarmigan and gyrfalcons is important because the birds are respectively at the bottom and top of the food chain.

“A lot of the research went into understanding the amazing intricacies between these two species,” he says. “They evolved together and depend on each other. But recently as everybody knows the tundra systems are in harm’s way and things are changing. In particular at the top of the food chain because the gyrfalcon is dependent on the whole thing working properly. What we’re seeing is a change in the birds’ ability to maintain their populations.”

Scientists recently counted gyrfalcon eggs in the Ogilve Mountains in central Yukon as part of a falcon survey.

Mossup says the predators are relatively easy to monitor because they build nests in the same place year after year.

“It’s all helicopter work. We go to the nests every year, see who’s there and how many babies they have. The ptarmigan is a matter of going out in the tundra with skis and snowshoes, monitoring how many are in a given area.”

Mossup has studied birds for 40 years. He says he is not certain the birds’ decline is irreversible. Still he says it is a curious anomaly in what is usually a well-balanced natural system.

“For the ptarmigan, it won’t dissapear. But those wonderful peaks we’ve seen in the past, we’re hoping they will restablish themselves. But over the broad scale, so far we haven’t seen it happen.”

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