At the top of the globe in the Canadian Arctic Archipelago, near the North Pole, a thin layer of soil above the permafrost thaws for just three months each year. When it does, the tundra bursts into bloom. The flowers are favorite summer foods of the Peary caribou, Rangifer tarandus pearyi, a petite, white-bearded subspecies of reindeer. With their noses stained red from the flowers of purple saxifrage, they are truly red-nosed reindeer in the summer. But foraging for flowers under summer’s midnight sun is a short-lived luxury. Finding food in winter has always been harder, and climate change is only making the problem worse.

Climate is changing twice as quickly in the Arctic compared to the global average. As winters get warmer and wetter, precipitation that falls as rain and then freezes on the ground is increasingly trapping the animals’ food below a crust of ice. Furthermore, declining sea ice is hampering their ability to move from island to island to find enough to eat. Set against a myriad of other ecological challenges, these environmental shifts are putting considerable pressure on the Peary caribou. But the latest scientific findings are informing conservation efforts and provide some reasons to be optimistic about its future.

It’s tough to precisely track the number of Peary caribou in Canada’s vast northern reaches. From the piecemeal data that do exist, scientists estimate that 13,200 adult Peary caribou now roam the Arctic Archipelago. That’s more than the 1996 estimate of 5,400 individuals, a low point attributed to winter die-offs from unusually deep snow and food shortages due to ice. But current numbers are still less than the 22,000 estimated in 1987. And although a recent modest rise in numbers prompted the Committee on the Status of Endangered Wildlife in Canada to suggest down-listing the Peary caribou’s status from endangered to threatened in 2015, scientists are concerned that populations might not be able to rebound to historic sizes if the environment changes too much.

One particular weather pattern is freezing the Peary caribou’s assets. The reindeer can forage just fine in snow, provided it is not too deep, nosing through the powder to reach the underlying vegetation. But as the Arctic warms, precipitation increasingly takes the form of rain. When rain falls onto snow in the High Arctic winter, it creates a sticky situation that soon freezes solid. The ice that forms on the soggy snow’s surface or in layers below can prevent Peary caribou from accessing the plants they need to survive. 

Even if the animals survive these difficult freezing events by finding alternate foods, or moving elsewhere, these dips in dietary intake may have consequences in the breeding season. “Females need a certain level of fat in order to reproduce in the spring,“ says Cheryl Johnson of Environment and Climate Change Canada, the country’s environmental science agency. During particularly harsh winters, with deep snow or rain on snow followed by icing, the number of Peary caribou calves observed the following spring can drop to zero.

Scientists have long debated the impact of these rain-on-snow and subsequent icing events on Rangifer tarandus—the species called caribou in North America and reindeer in Europe and Asia. In 2010, Nicholas Tyler, a reindeer researcher at the Center for Sami Studies at the University of Tromsø in Norway, published an analysis of all of the available data for rain-on-snow events in North America and Eurasia. He found little evidence for rain on snow being universally dire for caribou and reindeer. It’s an idea that over time, he says, achieved mythical status amongst researchers based on what he calls “enthusiastic interpretation of sometimes meager field data.” He says rain on snow may be important in some populations some of the time, but not in all populations all of the time.

Now, though, advances in data analysis from remote sensing are allowing a more rigorous look at how rain on snow and icing affects reindeer. Previously no one had actually examined whether rain-on-snow events had become more frequent in Canada’s High Arctic, Johnson explains. So she and her colleagues at NASA and at Canadian universities in Quebec and Ontario used satellite data to detect and quantify rain-on-snow and icing events across 18 High Arctic islands. They then assessed how well those occurrences aligned with caribou numbers.

One of Johnson’s collaborators, remote sensing expert Alexandre Langlois of the University of Sherbrooke, notes that rain-on-snow and icing events can be detected using passive microwave radiography data collected by satellites since 1979 to image the earth.

How can satellites detect ground-level phenomena? “Everything that has temperature emits thermal energy,” Langlois explains. The ground emits microwave radiation and snow scatters the signal. “But when you add water from rain, it changes the pattern completely,” he says. Computational algorithms developed by Langlois with University of Sherbrooke colleague Caroline Dolant and others can now detect rain periods, melt periods and ice patterns from the twice-daily satellite passes. Those data provide nearly four decades of coverage for the Canadian Arctic Archipelago, which, although limited for a climate record, is “one of the longest satellite time series that is available,” Langlois says.

Examining the microwave data, Johnson and her colleagues found a clear signal that rain-on-snow and icing events have increased in frequency since 1979. Areas with rain-on-snow increases in winter coincided with areas with decreases in caribou numbers the following summer, though it is unclear whether caribou declines reflect mortality or emigration to other areas outside the monitored range. Nevertheless, “if we can understand where these [rain-on-snow and icing] events occur, the frequency of that occurrence, and how spatially that might change through time, then we can assess which areas are at less of a risk,” Johnson says. The next step is to generate maps with finer scale data that can help conservation managers focus their efforts on lower rain on snow and icing areas where Peary caribou are more likely to thrive.

Rain on snow and icing are not the Peary caribou’s only challenges, however. Although these reindeer lack flippers and other traits associated with ocean-faring creatures such as whales, Peary caribou are, in fact, marine mammals. For centuries they have trekked from island to island across the sea ice in search of food. Now that sea ice is disappearing. Forming later and thawing earlier each year, the caribou’s inter-island highways are fading away.

In addition to keeping the caribou from reaching food sources, the loss of the ice highways could jeopardize the animals in another way. A new study published in 2016 in Biology Letters by Trent University doctoral student Deborah Jenkins and her collaborators analyzed Peary caribou tissue, antler and fecal samples collected across the Canadian Arctic Archipelago. Combining genetic analysis with remote sensing and climate change projections, they found evidence that Peary caribou in the Arctic Archipelago already have less gene flow between populations than continental caribou (a different subspecies) in the lower Arctic mainland. The authors predict that reduced bridging between islands in future will further limit Peary caribou gene flow because isolated populations have fewer opportunities interbreed.

But Johnson says that much more work needs to be done to understand where, when and how many Peary caribou cross the sea ice in order to determine what the loss of that ice may mean. And it is not only loss of sea ice itself that may impact Peary caribou crossings: as Arctic waters open up, shipping traffic is increasing, with unknown effects on these animals.

Climate change is just one of a multitude of factors affecting Peary caribou numbers. Fluctuations in population sizes of predatory wolves and polar bears, as well as still poorly understood interactions with herbivorous musk oxen that may compete for similar food, could also impact this small reindeer. At this point, no one is certain if the current upswing in Peary caribou numbers is part of the natural cycle of things, Johnson says. In her research, Johnson collaborates closely with Inuit community members and indigenous knowledge has been integrated into every aspect of her research, from helping to develop hypotheses to mapping caribou habitat and identifying where and when they cross the ice. “Without their knowledge we would have very, very little information,” Johnson observes. Indigenous knowledge, she explains, suggests that Peary caribou numbers have always fluctuated wildly through time. The current low numbers may thus be part of a very long-term natural cycle that will eventually usher in larger numbers.

Caribou researcher Micheline Manseau of the government agency Parks Canada, shares Johnson’s cautious optimism about the fate of the Peary caribou. Even with the predicted eventual loss of most sea ice, it’s not the first time in their evolutionary history that these caribou have had to change their movement patterns. There is evidence that some of Peary populations have gone through genetic bottlenecks in the past. Manseau suspects the creature will be able to thrive on the larger islands, which can be more than twice the size of Maine.

Other evidence supports this hopeful outlook for Canada’s diminutive, red-nosed reindeer, too. Carbon dating of ancient poop suggests that Norway’s Svalbard reindeer, which are similar in many ways to their Peary cousins, arrived on their now isolated Arctic archipelago 5,000 years ago. Crossing the sea ice from Eurasia, and becoming stranded there some time later, the Svalbard reindeer are “living proof,” Tyler says, “that these island populations can exist for a long time.”