Why don't the caribou cross the road?
That is the question raised by a new study into caribou behavior around the road used for delivery of ore from the huge Red Dog Mine in Northwest Alaska.
The decade-long study, published in the journal Biological Conservation, reveals that about a quarter of the caribou that encounter the 53-mile mine road balk at crossing it during their fall migration, causing them to delay their walk south.
The study, which uses data from tracking devices worn by some of the animals in the Western Arctic and Teshekpuk herds, solves a mystery that for years has puzzled veteran biologist Jim Dau, a study co-author.
Dau is retiring after decades of work in the region for the Alaska Department of Fish and Game and has much experience watching the movements and migrations of the massive Western Arctic caribou herd. Since the mine was built in the 1980s, he has watched caribou approach the raised gravel road that connects the mine's ore extraction site to its Chukchi Sea port.
Some caribou march over it "as if it doesn't exist," Dau said. Some walk parallel to it or mill about it, he said. But he did not know until now that some turned around to walk an extra 100 miles or so away from it, he said.
"Until I had really looked at that satellite collar data, I had no idea that some of them were walking all the way back to Point Hope," he said.
The results send a warning about any future roads that might be built across caribou habitat -- specifically, Dau said, a proposed 200-mile industrial road to the Ambler mining district that is being contemplated by state officials and was the inspiration for the research.
In contrast to the Red Dog Mine road, which is encountered by only a small subset of the caribou population, the proposed Ambler road would cut right through the heart of the territory used by the Western Arctic caribou herd, said Dau and a colleague.
"You could have a new road that comes in and it bisects the core corridor of the migration," said lead author Ryan Wilson, who is now a biologist for the U.S. Fish and Wildlife Service but was with The Wilderness Society and working independently when he did this study.
Other co-authors are Kyle Joly of the National Park Service and Lincoln Parrett of the Alaska Department of Fish and Game, both experts in Western Arctic and Teshekpuk caribou herd management.
The study analyzes the fall migration routes taken by 216 female caribou between 2004 and 2013. Because caribou travel in large groups, and because the sophisticated GPS collars used are expensive and difficult to install on animals, each collar-wearing caribou is considered to represent hundreds or thousands of herd members.
Of those 216 collared caribou, 32 walked within 15 kilometers of the Red Dog Mine road. Twenty appeared to have no trouble crossing it during the fall migration south, the results showed. But eight turned out to be "slow crossers" that took, on average, 10 times as many days to get across the road as the "normal crossers."
It took an average 33.3 days for the slow crossers to make it from the start of their fall migration to the other side of the Red Dog Mine road, compared to just 3.1 days for the normal crossers, according to the findings.
Four of the collared caribou included in the study never ventured across road at all during their fall migration and wound up wintering in far-north areas instead of spending the season with most of the 200,000-animal Western Arctic herd in the areas south of the Brooks Range, according to the findings.
The slow crossers walked, on average, about 300 kilometers more in their fall migration than did the caribou that crossed the road. Once they got to the south side of the road, they traveled 60 percent faster than the animals that crossed without delay. To catch up to the caribou that crossed earlier, the slow crossers "put on the afterburners," Dau said. "What used to take them two to three weeks to go through an area -- they can do that in two or three days," he said.
That means, though they walk longer and wait later to go south, the caribou wind up in the same wintering grounds at the same time, except for a few that stay up north and don't cross the road at all, he said.
It is not clear what is causing some of the caribou to avoid the lightly traveled road, Dau and Wilson said. But road-leery caribou seem to lead others away from the site, they said.
"What the elders have told me for years and years and years is, 'You just don't mess with the leaders,'" Dau said. "I think what the elders have been telling me for 25 years applies to the road."
Other roads have been shown to disrupt caribou migrations. In Canada, where populations of woodland caribou are classified as endangered, threatened or at risk, logging roads in some boreal regions are considered an important factor in causing declines.
Whether the Ambler access road will be built is unclear. Some work on environmental studies would be funded in the coming fiscal year under the budget submitted by Gov. Bill Walker, but there has been no decision on following through with the project. There is some strong opposition in communities along the would-be road corridor, the state is facing fiscal woes that might doom big projects and the main company eyeing Ambler mine development has admitted to its own financial troubles,
The road itself, if built, would not displace a large amount of habitat, concluded a 2014 study by Wilson, Joly and others. But impacts from roads can be multifaceted and cumulative, said that study and the new one.
"Developers and resource managers should consider the full suite of effects a road could have on migration and not simply whether animals will cross or not," the new study concludes.