Wildlife populations in the Yukon have never been static and fixed. Mammoths and mastodons, moose and bison, have all come and gone at various times, shifting their ranges or dying out altogether in response to changes in the climate. Over the last few decades, a number of species have been moving north into the Yukon, and some people wonder how much global warming is driving these movements.

Mule deer have been making inroads for a few decades, white-tailed deer show up occasionally, elk are migrating into southeast Yukon, and sightings of the elusive cougar continue to trickle in. People are also noticing changes among the birds spotted at their backyard feeders.

Change in nature is normal. The fossil record tells us that moose were here during the last Ice Age, but according to oral history, spotting a moose in most parts of the Yukon was a rare event a century ago. Anthropologist Catherine McClellan, in her book "Part of the Land, Part of the Water," speculates that moose began moving back north into the territory between about 1875 and 1900.

Now it is estimated that there are about 60,000 moose in the territory, and they are well-adapted to life in this part of the world. But some of the new arrivals have some distinct disadvantages when it comes to northern living. Unlike caribou, mule deer have small hooves that do not efficiently distribute their weight when travelling on snow. The deer's over-sized ears may also be a problem.

Manfred Hoefs, chief of habitat and endangered species in the Yukon's Renewable Resources Department, has seen mule deer with frost-bitten ears on two occasions. In the early 1970s he was out near Kluane Lake with Dr. Valerius Geist, a renowned sheep and ungulate biologist, when they spotted two mule deer with frozen ears. Geist commented how the injuries were a clear sign that these animals were at the northern limit of their range.

Hoefs saw another mule deer with frozen ears on the Takhini Hot Springs Road in the mid-1970s. He estimates that there are now somewhere between 500 and 1,000 mule deer in the territory. "In the last 20-30 years, they have been reported all over the southern Yukon, even as far north as the Dempster Highway. There are definitely signs that they are spreading out," he says.

Hoefs does not doubt that a warmer climate has allowed mule deer to establish populations in the north. He points out that extended periods of frigid weather have become much less common over the last few decades. But he also thinks that one severe winter could wipe the mule deer out again.

Elk were reintroduced into the Yukon in the early 1950s, but now these animals are also migrating into the southeast Yukon under their own steam. "Outfitters and hunters and trappers have mentioned them. During the hunting season they have been spotted in the river valleys draining into the Liard. We're not talking big numbers, but this is the first sign that they are moving north."

Hoefs says that deer can populate new habitat more quickly than elk because deer have a much higher reproductive rate. "They can have twins every year so the population can explode in a hurry. We also figure that deer are more tolerant of human activities as they are often seen in agricultural areas," he says.

A few summers ago, a white-tailed deer was killed on the Alaska Highway near the Kusawa Lake turn-off, proving the presence of this species in the territory. Antlers from a white-tailed deer were also found in the Ross River area, and conservation officers saw two white-tailed deer in the Minto area.

In 1996 a white-tailed deer was shot while swimming across the Mackenzie River only 100 kilometres south of the Arctic Circle. To date this is the most northerly sighting of this species.

Some people think that cougars could be following the deer north, and many of the sightings of these big cats seem to match up with areas where mule deer have also been seen. Hoefs says there have been about 200 reported cougar sightings over the last few decades.

Last May, a man said that he was attacked by a cougar when hiking near Kusawa Lake. A few years ago there were several independent sightings of cougars on the Dempster Highway. One was reportedly shot near Klukshu some years ago. Another cougar was reportedly killed when hit by a Winnebago near Rancheria, but the driver was said to have taken the carcass with him.

Hoefs does not doubt that there could be some cougars around, but says its strange that department officials have still seen no hard evidence. "There is lots of indirect evidence, but we would still like to have a hide or a skull to be absolutely sure," he says.

Birds are considered to be an even better indicator than mammals of climatic change as they are more mobile. The accounts are anecdotal, but many people comment that there seem to be more Magpies around than there used to be. Jim Hawkings, a biologist with the Canadian Wildlife Service, says annual bird surveys have shown that more Ring-necked Ducks and Northern Shovelers are breeding on Old Crow Flats. He has also noticed changes at his home feeder.

"There seem to be more Red-breasted Nuthatches around than there were during the mid-80s," he says. Hawkings speculates that some birds are taking advantage of the warmer climate and expanding their range.

Hoefs sees global warming playing a role with mammals as well, but also points out that "in evolutionary terms, the Yukon is not very old. In the southern Yukon the ice only retreated 12,000 to 14,000 years ago, so animal populations are still evolving and expanding their range."

Having species expand their range to the north might sound like a good thing at first glance, but there is always a downside. The animals, birds and plants living here now are adapted to the existing environment, not a warmer one. Also the Yukon's colder, drier climate keeps out many parasites found in the south.

Last summer Philip Merchant, a wildlife technician with Renewable Resources, investigated several reports of ticks, an unusual occurrence in the Yukon. He was relieved to find that it was probably a species associated with horses, and that they likely arrived on horses or dogs brought into the territory. He thinks it is unlikely that these ticks could persist for more than one generation in the existing Yukon climate.

But he warns that a 1-2 degree increase in the annual temperature could allow "the dreaded moose Winter Tick" to survive here. This parasite can kill moose, the host species, or stress them enough to be more vulnerable to predation.

"There are an awful lot of things about climate change that you do not think about at first, but you have to remember that our existing environment, and it's plants and animals, is based on the conditions we have here now, and a warmer climate could change that," he says.

For more information on Yukon wildlife, contact the Yukon Department of Renewable Resources at 667-5652.