Last updated: January 20, 2025
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The Great Video Reveal: Emerging Tech Tracks What Caribou Do
Caribou—a type of deer closely related to reindeer—are intimately connected to their Arctic environment, which is experiencing rapid climate change. These animals are notoriously hard to study, but new video camera collars put the spotlight on how they’re responding.
By Kyle Joly and Marie Lawrence
Image credit: Bureau of Land Management and the University of Montana
Once upon a time, you could find millions of wild caribou—known as reindeer in Europe and Asia—across North America. Now they’re only found in Canada and Alaska, where they are the most heavily used terrestrial species by northern subsistence hunters. They’re also an integral and interconnected part of the Arctic environment. But many caribou herds are in rapid decline, including the Fortymile Herd in east-central Alaska and Yukon Territory. This herd had about 30,000 individuals in 2024, down from around 80,000 in 2017. Some of this decline is due to climate change, which, among other effects, is altering the availability of food, lowering the herd’s fitness and reproductive success.
Using GPS video camera collars and mathematical modeling, researchers from the University of Montana and several government agencies investigated factors that affect how the Fortymile Herd obtains food during summer. They recently published their results in the Journal of Animal Ecology. This new type of collar enabled the researchers to study the animals up close, on a small, “bite-sized” scale, something rarely done before. Their findings have implications for the continued health and welfare of this vital species—and its Arctic environment.
Image credit: University of Montana / L. Ehlers
Analyzing “Bite-Sized” Impacts
Density-dependent habitat theory says that animals (like caribou) that don't defend their territories will first use the best resources to stay healthy. But as more of them gather in the same area, they start using lower-quality resources to avoid competing with one another. Their ability to reproduce can decrease when overcrowding causes them to compete for food. These concepts are borne out by large-scale scientific studies, which focused on huge areas or estimated food type based on landcover vegetation classes.
But not much is known about how such intraspecific competition affects behavior on a smaller scale, like when and where animals forage. The Journal of Animal Ecology study aimed to help fill that gap, assisted by new technology in the form of GPS video camera collars. Camera collars let the scientists watch the animals remotely to see what they did and where they went. This helped them understand how competition for space and food affected the herd’s behavior.
They classified the caribou behaviors they saw into six categories: eating, ruminating, traveling, stationary awake, napping, or other.
Alaska Department of Fish and Game staff placed GPS video camera collars on 30 adult female caribou, and the researchers tracked them. Aided by citizen scientists and botanists, the researchers analyzed the information from more than 18,000 of these videos. They classified the caribou behaviors they saw into six categories: eating, ruminating, traveling, stationary awake, napping, or other (licking soil for minerals, wading, drinking, etc.). They identified over 7,000 food items from videos where they saw caribou eating, which they also grouped into categories like lichens or shrubs.
The study authors then used statistical models to understand how the caribou made decisions. First, they tracked what the caribou did in different situations. They used this information to create behavior and food-choice models that predicted how caribou would act. The models considered factors like available plants, weather, wildfires, insect presence, and terrain. The researchers also looked at how much space the caribou used over time, as this could affect their behavior. The study authors removed “collinear” factors (those that were so similar or so related to each other they would mess up the results). Then they picked the models that best predicted caribou choices.
Foraging Factors and the Caribou-Lichen Connection
Lichens are a distinct group of organisms formed by a symbiotic relationship between fungi and algae, which interact and gain benefits from living together. Lichens play a unique role in an ecosystem. They break down rocks into soil, recycle essential elements like nitrogen, feed animals, and can indicate air pollution levels. Caribou and lichens are intricately connected. Lichens are the caribou’s primary winter food and a preferred food in warmer months.
Image credit: Bureau of Land Management and the University of Montana
Image credit: NPS / K. Joly
Libby Ehlers, PhD, lead author of the study, said they found that lichen herbivory “was lower where caribou use was high, possibly because there is lower biomass of lichens than shrubs in the summer.” The study results showed that the caribou preferred eating shrubs, particularly willows (Salix species), over lichens, even when lichens were more abundant. This makes sense because shrubs are more nutritious during the summer. As caribou need more food in summer, they tend to eat more shrubs, which can recover quickly from grazing.
Heavy use of an area by the herd in summer could deplete lichens through grazing and trampling. Unlike shrubs, lichens can take 20 years or longer to recover.
But lichens were still a favorite food, and because the Fortymile Herd’s summer and winter habitats overlap, heavy use of an area by the herd in summer could deplete lichens through grazing and trampling. Unlike shrubs, lichens can take 20 years or longer to recover. Shrub expansion due to climate change could also cause lichen reductions, for example from disturbance or wildfire. These factors could lessen lichen availability in winter, leading to poorer nutrition and lower caribou calf survival rates.
Image credit: NPS / K. Joly
“Insect harassment can be intense in interior Alaska, which can drive caribou to high-elevation habitat with little to no forage.”
The abundance of biting insects in Arctic regions during summer is legendary. There are, for example, an estimated 17 trillion mosquitoes just in the State of Alaska during the warmer months. The effect of insects like mosquitoes, warble flies, and nasal bot flies on caribou can be profound. Harassment by insects often causes the animals to gather in large groups and move to places where there is less food and fewer plants to eat. “Insect harassment can be intense in interior Alaska, which can drive caribou to high-elevation habitat with little to no forage,” said Ehlers. She and her coauthors found that caribou ate less when insect harassment was high. Strong winds and lower temperatures reduced this effect. But climate change, with its warmer temperatures and changing wind patterns, could increase it.
Density Dependence On a Small Scale
All those camera collar images showed Ehlers and co-authors that caribou are less likely to eat lichens but more likely to eat shrubs in places where the animals gather in large numbers. This small-scale density-dependent effect is consistent with those other, larger-scale studies mentioned earlier. It shows that overcrowding affects caribou foraging behavior even when observed on a small scale, potentially influencing the herd’s reproduction and survival.
Caribou inhabit some of the most remote areas remaining on the continent and are almost always on the move. This makes studying what they eat and why very difficult. This study relied heavily upon data produced from caribou-borne camera collars. They enable researchers and citizen scientists who classify the images to see exactly what caribou are doing in vast, distant areas without having to track them with planes or travel there. New technology like this can shed light on the potential for caribou to overgraze resources, how climate change may affect caribou populations, and what subsequent effects that could have on the Arctic environment.
About the authors
Marie Lawrence is the editor of Park Science magazine.