Though abundant over much of mainland Alaska, snowshoe hares were, until recently, absent from the state's northernmost Arctic region.
When did they arrive, and why?
A new study says the long-eared, big-footed hares, denizens of the boreal forests of northern North America, likely became established in Arctic Alaska in the middle or late 1970s, following the growth of tall shrubs in more northern areas brought on by gradual warming.
The study, by scientists from the University of Alaska Fairbanks, the Alaska Department of Fish and Game and the National Park Service, was published in the November issue of the journal Global Change Biology. It links changes in spring snowmelt, far-north vegetation and temperature with animal observations, historical trapping records and other data.
The study concludes that shrubs in riparian areas of the Arctic -- that is, along stream and river banks -- grew tall to support snowshoe hares sometime between 1964 and 1989, a finding that aligns with reports of the animals settling in at about 1977 or 1978.
While many other climate-change studies use past and current conditions to forecast the future, this project was different because it sought to understand things that happened decades ago, said lead author Ken Tape, an ecologist at UAF's Institute of Northern Engineering.
The idea was to "rather than predict the future, see if the predictions hold in the past," he said.
Based on evidence from personal accounts and written records, snowshoe hares appear to have been absent from the farthest north regions of Arctic Alaska prior to the 1970s. Scientists interviewed long-term residents, looked at trapping records, which lacked mention of snowshoe hares, combed through written records left by military personnel and researchers stationed in places such as Umiat, and in some cases interviewed those now-elderly scientists.
But changes on the ground that occurred over decades created hare-friendly conditions well north of Anaktuvuk Pass, previously the northernmost point of the hares' range, Tape said.
"In some ways, we have a warming experiment that is over a century old," he said.
Peak spring snowmelt has advanced 3.4 days per decade earlier over the last 30 years, according to the study. Photographic records dating back to the mid-20th century show that shrub cover has increased markedly along rivers and on slopes, the study notes; summers are warmer, growing seasons longer and the height of shrubs along river areas increased by about 78 percent.
Snowshoe hares need shrubs in river areas to have a mean height of at least 4 to 4.5 feet, and that threshold was achieved in the Arctic area about three to four decades ago, the study says.
Snowshoe hares aren't the only relative newcomers to the Alaska Arctic's animal kingdom. If the bigger shrubs drew the hares, the hares drew predators that target them, Tape said.
"We believe the lynx followed the hare," he said.
Historical records show lynx were absent or rare on the North Slope for at least the first half of the 20th century, the study says. Fish and Game biologists conducting an aerial survey of moose in 1998 made the first reported lynx spotting since midcentury, and in recent years lynx have shown up in North Slope trapping records, indicating a sizable population, Tape said.
Even moose are somewhat new to the farthest-north areas, colonizing the area in the 1940s, the study noted.
The population shifts correlate to habitat changes, Tape said. "You look at their habitat -- shrubs are moving northward and getting taller all along the northern edge of these species' range," he said.
If snowshoe hares living in Alaska might be considered climate-change winners because of their expanded territory, populations of the species in habitats farther to the south appear to be losers.
In parts of the Rocky Mountains, winter snows are melting too fast for many snowshoe hares' seasonal fur changes, leaving the animals white against a brown background and easy targets for predators. And a similar fur-color mismatch has affected a different species, mountain hares, in Sweden.