Caribou show biodiversity within a single species

What does all of the North share, across all continents - apart from that January feeling that winter will never end? Caribou.

By Claire Eamer

What does all of the North share, across all continents – apart from that January feeling that winter will never end? Caribou.

They’re called reindeer in some parts of the world and caribou in others, but they’re all the same species: Rangifer tarandus. And they’re the dominant large herbivore, or plant-eater, in the circumpolar ecosystem. In fact, in most parts of the North, they’re the only large ungulate.

Their secret? “Caribou have evolved to exploit a lichen-dominated taiga,” explains Whitehorse caribou biologist Don Russell. Not many animals – and no other large animals – thrive on lichens, let alone in the numbers that caribou reach.

But does that mean there’s not much diversity in the Arctic? In this, the International Year of Biodiversity, when we’re struggling to preserve Earth’s amazing variety of life, it looks as if the North has already lost the battle.

Not so, says Russell, who is co-ordinator of the CircumArctic Rangifer Monitoring and Assessment Network (CARMA), an international organization concerned with the state of the Arctic’s wild caribou and reindeer. Despite belonging to the same species, caribou and reindeer vary considerably in size, shape and behaviour from place to place and from herd to herd.

Perhaps the oddest member of the tribe is the Svalbard reindeer, the Shetland pony of the reindeer world. Svalbard is Norwegian territory, a small group of rocky islands about halfway between the Norwegian mainland and the North Pole. Isolated by hundreds of kilometres of ocean from any other land, Svalbard is home to a distinct population of reindeer, small, with short legs, snubbed muzzles, and chubby, barrel-shaped bodies.

Svalbard reindeer aren’t designed to run, says Russell, but they don’t need to. The only large predators on Svalbard are polar bears, and they’re rarely interested in reindeer. On the other hand, those chubby bodies are important. In winter, Svalbard reindeer have to eat whatever and whenever they can. Most other caribou and reindeer eat lichens, which are available in winter, even if they’re under the snow. On Svalbard, however, there are few lichens.

“The Svalbard reindeer eat whatever greens up,” says Russell. In spring, they eat the first green shoots of sedges emerging beneath the previous year’s dry stalks. Through the summer, they work their way through the lush tundra plants, packing on as much fat as possible. The fat has to last them through the lean times of winter when they go on a crash diet, often losing almost half their autumn weight by spring.

There are island Rangifers in North America too: the Peary caribou of Canada’s high Arctic. Like Svalbard reindeer, they are smaller than mainland caribou, but there the similarity ends. Peary caribou are leggy and lightly built, more like deer than Shetland ponies. And they can run. They need to. Unlike Svalbard, their islands are not isolated. For much of the year, they are linked to each other and to the mainland by ice, providing easy access for predators such as wolves.

Most caribou and reindeer live on the mainlands of North America, Asia, and northern Europe, right in the midst of the predators, scavengers, and human hunters. Generally, they’re larger than the island caribou, and they can run well, for long distances if necessary. Herds like the Yukon’s Porcupine caribou travel thousands of kilometres in their yearly rounds.

Mainland caribou are divided broadly into two groups: barrenground caribou and woodland caribou. Most barrenground caribou migrate, and most woodland caribou stick to a small range all year. But not all. A couple of woodland caribou herds in eastern Canada migrate seasonally almost to the same degree as barrenground caribou.

Even within the barrenground group, there’s plenty of variety, says Russell. Researchers classify the herds into four groups by their calving patterns, he explained.

Swamp calvers, such as the Central Arctic herd, go to the polygon wetlands that overlie permafrost to calve. The wet, broken terrain gives them some protection from predators during the calves’ first, vulnerable days.

Upland calvers, including the Porcupine herd, migrate to the tussock tundra of the coastal plain. There, the wind keeps off harassing insects and the open country offers little cover for hungry predators. The lichen barren calvers, such as the Bathurst herd in the eastern Northwest Territories, head north to open tundra to calve, sometimes as far as the Arctic coast.

In Labrador and northern Quebec, where there’s little tundra range available, you’ll find the treeline calvers – the George River herd and the adjacent Leaf River herd. Together, the two herds number close to a million animals and are currently the largest herds in North America.

Where they calve affects the herds’ migration timing, health, and the factors that determine calf survival. For example, upland calving caribou tend to arrive on their calving grounds in poor physical shape. Between their wintering grounds and the coast, there’s usually little to eat but poor-quality evergreen shrubs and moss. The fresh, green, spring vegetation on their calving grounds is vital to them.

“Calf survival is quite dependent on the time of green-up,” Russell says.

Lichen barren calvers have the opposite problem. The Bathurst caribou arrive in fairly good condition because they can feast on energy-rich lichens all the way to their calving grounds.

“They have to because there’s nothing much to eat when they get there,” Russell says. In fact, within 10 days of calving, they move back south to better feeding grounds so that the cows can produce enough milk to sustain the calves.

Many of the barrenground caribou herds have been declining in numbers for several years. The lichen barren calvers have been hardest hit in Canada, while the two swamp calver herds, Central Arctic and Teshekpuk Lake, are the only herds not in decline. Russell says researchers still don’t know exactly what causes herd declines, but figuring it out is currently a top CARMA research priority.

For more information about caribou and reindeer and the communities that depend on them, go to the CARMA website at www.carmanetwork.com.

The Your Yukon column is co-ordinated by the Northern Research Institute at Yukon College. This column is sponsored by the CircumArctic Rangifer Monitoring and Assessment Network. A full list of funders and

all past articles are available at

www.taiga.net/yourYukon.

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