A rain-soaked mother nuzzles a calf lying on a thick mat of lichen in one picture. A herd of reindeer stampede across the wintry plain in another, kicking up snow into the camera.
Taken from GPS collars, these candid shots represent an unprecedented window into the lives of the last population of wild mountain reindeer on Earth, a herd of about 10,000 animals that roams Norway's Hardangervidda region. Reindeer—known as caribou in North America—are a type of hardy deer that have thrived in Earth's cold northern regions since before the last ice age.
"No photographer could ever take pictures like these," said Manuela Panzacchi, a biologist at the Norwegian Institute for Nature Research in Trondheim, who has been studying the animals for a decade. "This is giving some insight into what it is to be wild."
But they aren't just pretty pictures. The GPS cameras are helping Panzacchi and other scientists learn how roads and tourists thwart the ancient animals' historic migration routes in Norway, she said.
Norway's reindeer migrate annually between their summer calving grounds and their winter habitats, navigating 2,500 square miles (about 6,500 square kilometers) across Europe's largest mountain plateau. (Read about great animal migrations in National Geographic magazine.)
"Few people are aware that within the heart of Europe there still exist mass migrations as spectacular but more secretive than those in the Serengeti," she said.
"More important, few are aware that we're losing them right under our nose—with largely unpredictable consequences."
Since 2002, Panzacchi and her team have fitted 200 reindeer with GPS collars equipped with cameras with wide-angle lenses to record their movements and behavior.
That's because for most of the year, the animals live in remote mountain ranges mostly inaccessible to scientists, often navigating deep snow in temperatures as low as –22 degrees Fahrenheit (–30 degrees Celsius).
So far, the team's GPS data have revealed that human presence, such as a road, cabins, or even hikers, can hamper a reindeer's migration. (See Norway pictures.)
In a 2011 report, Panzacchi and colleagues showed that pregnant reindeer on their way to their calving grounds change direction and wander for days after they encounter evidence of people.
Norwegian reindeer are extremely wary of humans, since hunters kill up to 25 percent of the herd each year. Reindeer hunting has deep cultural roots in Norway. (Read about Scandinavia's Sami reindeer herders in National Geographic magazine.)
If thwarted by a road, the restless reindeer sometimes linger in their winter habitat, eating up all the lichen—which can take ten years to grow—potentially leading to starvation, her research shows. Or the reindeer may eventually feel comfortable enough to cross the road and then speed up to get to calving grounds, spending energy they don't have and perhaps endangering themselves or the calves.
"There's lots of evidence that caribou are affected by roads," said Jim Dau, the Alaska Department of Fish and Game's lead biologist for the western Arctic caribou herd.
Dau's findings that pregnant caribou are especially sensitive to roads—giving them a berth of up to 3.7 miles (6 kilometers)—are consistent with Panzacchi's, he said.
But at other times of year, even weeks after giving birth, female reindeer don't seem to mind roads, even traveling on them to escape insects, which aren't as prevalent on higher ground, Dau noted. (Related: "Moose Moms Prefer Traffic to Grizzly Bears, Study Says.")
These differing reactions partly explain why roads' influence on reindeer is controversial: "You have people who will argue [until they're] blue in the face that a road has no particular effect on their population," noted Perry Barboza, a wildlife nutritionist at the Institute of Arctic Biology, part of the University of Alaska, Fairbanks, who was not involved in Panzacchi's research.
But the animals' actions are not surprising. "It's the same with people—your response to a risk will change depending on your experience and your current conditions."
What seems clear is that development is changing how reindeer migrate in Norway. "It's something that's disappearing, and if we value it, we need to work it out," Barboza said.
That's especially true as construction of tourist cabins and roads along reindeer migration routes is on the rise, said Panzacchi. She noted that Norway's government is concerned, and has set up two reindeer management areas, in which they plan to identify migration routes and work with local governments to lessen impacts to the animals—for instance, by closing roads when the females are most sensitive.
In general, "the collars provide a whole new layer of information" for reindeer biologists, said Barboza, adding that Panzacchi's research is "brilliant" and "carefully collected."
For instance, the pictures help confirm the age and sex of individual animals in the herd, as well as show when calves are born and whether they die, he said. (See pictures of the planet's great migrations.)
"The collars can also collect information over much longer periods than we can directly observe on the ground, and with much less risk of altering the behavior."
Alaska Fish and Game's Dau, who has studied caribou since the 1970s, added that GPS-collar technology is "exciting," but "the one thing that scares me is more and more caribou biologists are sitting in their office and gazing at photos from a trail cam and dots on a map," he said.
"If you never get out in the field, you don't see the ice frozen on their faces, the hair that's cut off like a razor when they've been walking on ice-crusted snow."
Even so, Panzacchi said the intimate photographs help her understand reindeer better than ever. Images of the animals huddling for warmth in a blizzard, of calves taking their first steps, "made us perceive the vulnerability of these animals and, at the same time, their immense strength and resilience," she said.
"Hence, they reinforced that sense of wonder," she said, "that sometimes we forget."