Trail of the unexpected

As autumn arrives in Alberta's Waterton Lakes National Park, clumps of aspen and larch blaze among the evergreens sweeping from the lake shore to the feet of dizzying precipices. A pair of eagles soars in the silvery light above snow-powdered rock summits.

For my 36-year-old son Rupert, guide and survival expert, searching for grizzlies is business as usual. For me, fresh from England, it is something of a new departure.

The ferry slides alongside a landing-stage and we are the only hikers to step ashore. This is the foot of the trail that leads up to Crypt Lake, a "hanging lake" cupped among 9,000ft summits at the height of the Rockies. On the shingle we pull on fleeces and adjust backpacks. Rupert clips an aerosol can of pepper-spray bear-repellent to my belt. He clips a "noisemaker" to his pocket and we head for the trees.

At the start of the trail a wooden sign leans against a tree: "Bears seen here this morning." Already! My pulse quickens. "Grizzlies?" "I guess." Fingering my can, I scan the underbrush. How could such a thin jet deter a charging grizzly? And the noisemaker, slim as a pen, which detonates a blank .22 bullet with a whip-like crack - what use would that be against 300 kilos of determined bear?

But anxieties quickly fade as the forest cocoons us in silence. Carpeted by pine needles and veined with roots, the trail rises in steep hairpins through a fairyland of light and shade. Beams of sunlight slant between slender trunks of lodgepole pine, spruce and fir. Dwarf willow and maple glow lime-yellow and russet-gold in dappled shade. Dismembered fallen trees, trunks criss-crossed and blanched, litter the forest's boulder-strewn floor.

At intervals Rupert calls, "Hey, bear! Hey-hupp!" to forewarn bears of our advance. Contrary to popular belief, grizzlies are rarely aggressive and will charge only if surprised or, crucially, if you run. They are attracted to food left by visitors and will break into tents to find it. The human is not the target but inevitably the bear will be blamed if one is mauled or killed. From a standing start a fully-grown grizzly is as fast as a horse, able to maintain a speed of 30mph over a short distance. In the event of a confrontation, Rupert told me, stand your ground and look at the bear's chest rather than meet its eyes, to let it know that you are not challenging it. Talking calmly to the animal, ideally with your face slightly averted, you should then move slowly backwards. Normally, such action will defuse an attack and the grizzly will move on.

As we approach the tree line, dark clouds billow from the peaks ahead. Beneath twisted larches we pull on waterproof jackets. Just in time. A few heavy splashes, then the rain sluices down, battering our heads and shoulders with the force of a waterfall.

About half the area of the Canadian Rockies lies above the altitude of the tree line. We have reached the alpine zone - or tundra - where there is little shelter from the elements. The rain turns to sleet. The wind drowns Rupert's calls. Violent gusts whirl wet snowflakes under my hood. Rock shards avalanche into the emptiness below. Rupert is a blurred shape ahead.

Suddenly two hikers materialise from the mist on the trail above: a man and a girl, both drenched. We exchange hurried words. They have seen three grizzlies six hairpins up and clearly have no desire to linger.

We trudge higher. Sleet turns to snow. Rupert calls constantly. I grip my pepper-spray and count the hairpins.

Level ground at last. Rupert points at tracks and tell-tale "scat" in the snow. Grizzlies! The storm abates with surprising suddenness. Cloud dissipates to reveal whitened boulder-fields rising to a ridge topped by pale sky. Rupert's eyes are trained.

"Up there! See them?"

And there they are. Three large brown furry creatures, unaware of our presence, facing into the slope barely two hundred meters above. "It's a sow with two yearling cubs."

We move carefully along the trail to find a better viewpoint. The three grizzlies are closer now, rumps still towards us, the sow scooping rubble in search of roots and burrows. The cubs, almost as large as their mother, follow her example.

We watch motionless as the trio excavate with their powerful forepaws. Then the sow senses that something is amiss. Unhurriedly she turns to examine our presence, a length of severed white root dangling from her jaws.

My mouth is at Rupert's shoulder. "She OK?" "Yeah. She's just sussing us out."

Casually, as if to demonstrate her power, the sow rolls ponderously on to her hindquarters, forepaws hanging limp at her sides, revealing her massive bulk. Ears twitching, she gives us a long stare. The cubs follow suit.

Rupert's voice is almost inaudible. "Turn your head slowly to the left and look down."

Seconds tick by. Carefully, I glance back up. The three grizzlies have resumed their search for food. Gently and silently we back away.