Bird biologist Dave Mossop stopped his boat in the shadow of a cliff on the east shore of Lake Laberge, scanned the steep rock face with binoculars and then fired a shotgun to make a noise that would, hopefully, flush any resident falcons.

Biologist Dave Mossop scans the shore of Lake Laberge for nesting peregrine falcons. (photo: Erling Friis-Baastad)

It worked. A small, dark streamlined shape rose from the rock and circled high overhead.

"Holy smokes!" Mossop shouted. "I thought we'd see nothing today... just have a picnic. This is only the second peregrine I've seen on the Southern Lakes in 30 years!"

Soon the female peregrine was joined by a smaller male. But any hopes we had that they might be a loving couple were quickly dispelled.

"That's not a happy chase," he said. "She's giving him the old heave-ho. That's a stray who's not supposed to be here."

The female chased the male across the lake and then resumed her vigil from a skinny spruce on top her cliff.

"Peregrines maintain a territory of about two kilometres and they defend it vigorously," said Mossop.

The two laymen who were privileged to accompany the ornithologist on his survey Laberge survey June 24 were disappointed to learn the two peregrines weren't engaged in a romance that could result in little falcons. But Mossop didn't appear overly concerned.

"Peregrines are long-lived. They can take three to four years to set up shop. Come back in a year, they may be doing something."

The thrill for Mossop was that a peregrine is nesting on the lake at all. As recently as last summer, he'd traveled the Yukon River and hadn't seen falcons anywhere near this cliff.

"I'd often looked at that cliff and thought, 'If I were a peregrine, that's where I'd live.' She's the first peregrine on this lake in, holy smokes, 20 years."

The female falcon is the tip of a success story. Thirty years ago, the species had almost vanished from the Yukon. Across Canada, the peregrines had been failing to reproduce thanks to pesticides like DDT.

Such poisons were banned (in North America at least) and conservationists worked hard to protect remaining falcons and their nesting sites.

Back in the peregrine dark ages of the '70s and '80s, the Yukon had one nesting pair. Today there are 200 that we know of, said Mossop.

They are divided into five recognized sub-populations. The largest is in the Peel River drainage.

There are probably an equal number of non-nesting peregrines, he added. It's difficult to know for certain. Much territory must be covered to spot any at all, and unlike the case with ducks, which are hunted, peregrine leg bands aren't often returned.

Mossop, an instructor at Yukon College, belongs to the Peregrine Recovery Team, an organization that -- among other initiatives -- conducts major surveys every five years to determine the health of Canada's peregrine populations.

He has been taking part in the surveys since 1975.

A love of these beautiful birds might be sufficient motivation for ornithologists and other conservationists to take to the mountains and waterways with their binoculars, but the significance of the surveys extends beyond esthetics.

"Being at the very top of the food chain, the peregrine is an indicator species," said Mossop.

How well they are faring gives us an idea how well other creatures are doing right down the chain. "They allow us to keep a thumb on the pulse of the ecosystem."

A fluctuation in the pulse gave surveyors a scare again about 12 years ago, he said. Suddenly, the peregrines stopped reproducing yet again. Though populations remained fairly stable as more and more young falcons reached breeding age, the birds just weren't making more youngsters.

For a few frightening years, the reproduction rate dropped too low to sustain a peregrine population.

Fortunately, the young began hatching in good numbers again two years ago. While scientists are not certain just what caused the frightening glitch, Mossop believes "it's a climate thing affecting the food source."

The climate of the North is going through drastic changes and we're far from understanding how these will affect the creatures who live here.

One of the pleasures of accompanying Mossop on a peregrine survey is being able to share his enthusiasm for the big picture. His love of peregrines encompasses all facets of their environment.

Peering up the imposing cliff face of the falcon's home, he marveled at the rounded summit of the hill in which it sits in.

He painted a word picture the Southern Lakes area during the ice ages, when the entire region was covered by a huge glacier. "Imagine the weight and power of the ice that carved that rock so smooth."

A large cormorant conducted a fly-over of the boat and inspired further excitement. A pair is rumoured to be nesting on the lake, but they are not at all common so far inland in the territory.

An all-too-common bird on the lake inspires yet more awe. Herring gull colonies are burgeoning in the Yukon. "It's too bad we've given them such an advantage," said Mossop of the gulls. Human garbage dumps keep them fat and happy through the winter months.

"They have virtually no winter mortality. Virtually nothing likes them; maybe they just don't taste good.

"And they are completely omnivorous."

If he were to be reincarnated, he'd want to come back as a gull, said the scientist. They're designer survivors.

The gulls are crowding out other more delicate non-scavenger species like the elegant Arctic terns. But while gulls are serious predators of nestlings and the eggs of other birds, they don't pose a threat to the peregrines, said Mossop.

We'd already seen an angry peregrine in action, and the most courageous gull would be no match.

A spotted sandpiper flew past less than a metre above the shore. Mossop had said shore birds and ducks were the preferred food of peregrines. Was that sandpiper in danger?

Fortunately that shorebird species tends to fly very close to the surface creating difficulties for any peregrine that might want to swoop down from on high, he said.

However other shorebirds, like snipe and yellow legs, indulge in flight songs high up... often becoming falcon food.

"That's a poor-percentage play, as we say in hockey," said Mossop.

Above us the peregrine was conducting a survey of her own, on the lookout for just such an opportunity.