Road traffic has long posed a challenge to caribou on the North Slope. For decades, there has been a standard for oil field traffic heavy enough to disturb the animals: 15 vehicles per hour. Environmental studies and permits invoke that as the threshold at which caribou stop walking freely near and across roads.
Now a newly published study analyzing caribou movements at two oil fields shows that the traffic volumes that inhibit animals’ movements appear to be much lower: five vehicles an hour.
The study adds to a growing body of evidence that caribou are much more bothered by infrastructure and industrial activity than was assumed in the past, when existing North Slope oil fields were planned and permitted.
“Caribou are really sensitive. They’re really sensitive to human activity. And we’ve seen from past studies that they’re also sensitive to human infrastructure, and they really respond to it,” said Heather Johnson, a U.S. Geological Survey biologist who coauthored the study. “The key takeaway from the paper is they’re more sensitive to road activity than we had previously recognized.”
The results of the new study about road traffic and previous studies of caribou interactions with infrastructure have implications for existing Arctic Alaska industrial operations – and for expanded development, such as the massive Willow oil project that ConocoPhillips is building this winter and the proposed 211-mile Ambler Access Project road that would link an isolateding Northwest Alaska mining district to the state’s existing highway system.
The new study examines the movements of female caribou that have had radio tracking collars attached to them in and around the Kuparuk and Milne Point oil fields. In doing so, it tested the effects of human activity, adding to results from previous work by Johnson and others that examined how the presence of human-created infrastructure affects caribou. That research includes a 2020 study Johnson led that showed that caribou in the oil field areas, even after generations, continue to stay away from manmade features like pipelines, roads and buildings and show little sign of habituation to development, especially during the sensitive calving period.
The new road-traffic study and Johnson’s 2020 study focused on the Central Arctic Caribou Herd, currently estimated at 34,000 animals. By tracking the animals’ movements through the collar-derived data and road traffic through counting devices, USGS biologist John Severson, Johnson and coauthor Timothy Vosburgh of the U.S. Bureau of Land Management found that the caribou generally stayed away from roads, preferring spaces that were at least at least 1 to 3 kilometers — or about 0.6 to 2 miles — away from roads during the post-calving and mosquito seasons. During all the periods they were present in the oil field areas, caribou generally stayed away from roads with traffic levels of five or more vehicles an hour, the study found.
Caribou’s reluctance to cross or be near busier roads is seen despite long-standing rules intended to protect them, Johnson said. Oil field roads are closed to public use, authorized traffic is under speed limits that top out at 45 miles an hour and caribou are granted the right of way, “So it’s a very controlled environment where drivers are instructed to stop for caribou crossing,” she said. “And yet, even in that environment, you know, caribou are showing these responses.”
The 15-vehicle-per-hour standard dates back to the 1980s, when biologists used visual observations to compare caribou reactions in various settings ranging from undeveloped areas to areas with both roads and pipelines, said Johnson and Severson, the study’s lead author. Those studies predated the use of radio collars and the fine-scale movement tracking that they enable.
By correlating caribou movements with weather conditions, the new study found that it generally took conditions conducive to severe insect harassment – high summer air temperatures and low wind speeds – to motivate the caribou across more heavily trafficked roads to reach the cooler, windier areas along the coast or river bars that provide relief from biting bugs. “They become less risk averse,” Johnson said.
It is unclear how traffic deters caribou movement, whether through dust, noise, visual signals or something else, Severson said. But from what he has seen, there is often a noticeable response when the animals encounter traffic.
“Sometimes they’ll just stand there. Sometimes it seems like they kind of get freaked out and kind of run around a little bit. But it varies,” he said.
Average road traffic during the study period was less than 15 vehicles per hour, closer to 12 per hour in 2019 and 8 per hour in 2020, the scientists found. Rates varied a lot from road to road, they said, with traffic concentrated on the large main roads.
Since Central Arctic caribou are present in the oil fields for just a few weeks out of the year, operators have some available options for reducing traffic impacts on the animals, Johnson and Severson said.
A possible response from oil operators would be better timing of vehicle traffic by season or even time of day. “When insect activity is really high in the middle of the day, they could potentially reduce traffic then,” Severson said.
Teshekpuk and Western Arctic caribou may face different road challenges
Avoiding impacts may be more complicated at the Willow project being built farther west on the North Slope, however.
Willow overlaps habitat used by the Teshekpuk Caribou Herd, estimated at 61,500 as of 2022. Unlike the Central Arctic herd, which migrates north only for calving and the post calving period before venturing south to Brooks Range foothills well south of the established oil fields, most of the Teshekpuk herd remains on or near the western North Slope all year.
Caribou figure prominently in the environmental studies that led to the Biden administration approving Willow in March. In the supplemental environmental impact statement released by the BLM just before the approval, the word “caribou” is used more than 1,000 times just in the first volume. The document described the importance of caribou to traditional Native hunting and the federal government’s obligation to protect it and other subsistence resources. The document also notes differences between the Teshekpuk herd and the Central Arctic herd, and that the latter has been more studied for its impacts from oil development. That makes predicting impacts to the Teshekpuk herd more difficult, the document said.
On the positive side for the Teshekpuk herd, there will be a good opportunity for scientists and managers to track the impacts of oil development, said Kyle Joly, a National Park Service biologist who studies Alaska’s caribou. “They’ll have a lot of data as to what movements were like before development,” he said. That contrasts with the Central Arctic herd, for which predevelopment data “was in short supply,” he said.
There will likely be plenty of information about traffic interactions if Willow development is carried out as planned. A BLM document provides detailed information on projected road traffic at Willow, which according to the analysis is expected to top 3.1 million vehicle trips over the project’s 30-year lifespan.
During Willow’s first 10 years, when construction is underway, traffic on the oilfield road is expected to average 15.5 to 81.7 vehicles per hour, according to the supplemental environmental impact statement. For the 20 years of Willow operations to follow, traffic would be lighter, at 7.5 to 9.5 trips per hour.
The record of decision that approved Willow development includes some requirements for traffic controls to protect caribou, including periodic closures, but it invokes the long-used 15-vehicles-per-hour standard.
The proposed Ambler Access road would cut through habitat used by the larger but declining Western Arctic Caribou Herd, now estimated at 152,000 animals.
The most recent environmental analysis of that project, released by the BLM in October, describes expected traffic loads there. It cites a traffic estimate of 80 one-way double-trailer truck trips per day expected on the road during the early years of Ambler mine production. The rate is expected to reach up to 168 trips per day as other mines come into production, and the National Park Service has calculated a traffic rate of about seven vehicles per hour, the document says.
For the Western Arctic Caribou Herd, the very existence of at least one road appears to affect movement for some animals, past studies have shown. Those studies monitored movements of collared Western Arctic caribou from the herd and found clear patterns of road avoidance.
A study of collared caribou found that a significant percentage delayed their fall migrations when they encountered the 52-mile road that connects the Red Dog mine site, one of the world’s largest zinc producers, with its Chukchi Sea port. That road, officially called the Delong Mountain Transportation System, significantly slowed migration for parts of the herd, a 2016 study by Joly and some colleagues showed. An update to that study is in the works, but annual monitoring of collared animals shows that the “barrier effect” continues, with even longer delays in migration, Joly said.
Just what it is that the caribou dislike about the road is yet to be understood, though there are plans to try to find out, he said.
“Is it traffic? Is it noise? Is it dust deposits that affect the habitat along the road? Or is it something else?” he said.
The traffic-volume findings in Severson’s and Johnon’s study thus represent a big advance in knowledge, Joly said, even though the summer movements they studied among the Central Arctic caribou are different from the spring and fall migrations during which Western Arctic caribou might encounter the Ambler road.
The accumulated scientific evidence of the animals’ aversion to roads has rattled members of the Western Arctic Caribou Herd Working Group, an advisory panel composed mostly of members representing Indigenous villages dependent on caribou hunting for food and traditional culture.
The working group in the past has issued official positions against the Ambler road.
At the group’s annual meeting in December, Johnson presented her findings and the latest status reports and migratory patterns of the Western Arctic herd were reviewed. Members reiterated their concerns about the presence of roads
“My true thoughts, my heavy thoughts, are to continue to stand our ground,” co-chair Cyrus Harris of Kotzebue said.
Member Darrell Hess of Huslia agreed: “We have to fight it, because if we don’t, our kids are going to suffer. They’re going to say, what happened? Why did you let this go? I’m not going to let this go.” Others expressed a sense of fatalism or resignation.
If the federal government decides to build the road, “no way we’re going to beat the federal government,” said Vernon Cleveland, who is the group’s chair and represents the Inupiat village of Noorvik. “We’re playing Cowboys and Indians. I’m not a cowboy. I’m an Indian. The cowboys win all the time.”
One member, William Bernhardt, spoke up in favor of the road and the Ambler mine development, saying it would help lift the region’s economy and provide a future for residents. “Life’s not easy up there for people who have to work. Most of the opposition up there are people who are on food stamps or welfare,” said Bernhardt, who represents the Upper Kobuk River area, which is relatively close to the site where producing mines would be developed.
Throughout North America, road development has been cited as one of several reasons for caribou population decline problems. The governments of Canada and its province of British Columbia both describe habitat fragmentation caused by roads as a major problem for that country’s dwindling boreal caribou herds, which live in more southern regions. The existence of even seasonal winter roads in the Northwest Territories were shown to inhibit crossings by more northern, tundra-dwelling caribou, according to a 2023 study by University of Northern British Columbia scientists who also tracked movements through GPS collars.
For Alaska’s Western Arctic herd, the Red Dog mine road has long been virtually the only road with which caribou interact during migration, Joly said. But the Kivalina Evacuation Route was completed in 2021 as part of the Inupiat community’s response to accelerated coastal erosion and flooding. It runs about 7 miles roughly parallel to the Red Dog road.
Even prior to any construction of an Ambler road, Joly said, there is some emerging evidence that the new Kivalina road is also inhibiting caribou movement.
