40-Mile Caribou

Project Lead: Libby Ehlers, PhD Candidate

The Fortymile Caribou Herd in Alaska and the Yukon is one of North America’s most important migratory caribou herds, straddling the border of the US and Canada. It has been the focus of study for the past 60+ years in Canada and Alaska. In this NASA ABoVE affiliated project, PhD student Libby Ehlers is collaborating with the BLM, Alaska Department of Fish and Game, Yukon Fish and Wildlife, and the National Park Service to understand habitat and population dynamics for this important caribou herd. Recent growth of this herd to over 80,000 caribou has prompted this study on habitat relationships to assess whether the Fortymile Caribou Herd has approached nutritional carrying capacity and how that may affect habitat and vegetation dynamics.

caribou

Two bull caribou of the Fortymile Caribou Herd travelling in their summer alpine tundra habitat (Photo credit: Jim Herriges, BLM and Libby Ehlers, Univeristy of Montana)

For her PhD research, Libby is working to understand caribou forage availability together with Katie Orndahl at Northern Arizona University, in collaboration with Scott Goetz and his ABoVE project focusing on vegetation change. This work combines field-based vegetation sampling with UAV drone and remote sensing data. Using this, Libby will then examine caribou diet using field sampling and GPS radiocollars equipped with a camera (see video below) to understand spatial variation in herbivory. Libby will then integrate spatial models of forage to caribou resource selection and bottom-up aspects of demography, together with Alaska Department of Fish and Game.

GPS Video-Camera Collars

This video, showing a caribou browsing on willow (Salix pulchra), was taken from a GPS video-camera collar worn around the neck of an adult female caribou. We are using GPS video-camera collars to better understand the summer diets of a migrating caribou herd that extends across Alaska, USA and the Yukon Territory of Canada. Willow is a favorite summer food type for caribou as it is highly digestible and packed with beneficial nutrients and proteins. Female caribou are unique in that they are the only members of the deer family to grow antlers (bonus question: why?)! As we can see in this video, another female companion shows off her beautiful velvet antlers while eating willow.


Bear flower (Boykinia richardsonii) is a favorite of bears, but also of caribou! This video shows an adult female caribou, in addition others in the herd, foraging on a beautiful patch of bear flower leaves. You can see the flowers have already bloomed and dropped, but the leaves are still a favorite food when it is available. Videos like these also provide researchers with a better understanding of how caribou use certain types of forages throughout the plants life stages, or phenology, throughout the summer months.


Caribou are known to eat mushrooms as they are valued for their high protein and palatability in the late summer months. Videos like these, from GPS video camera-collared caribou, provide insight into where and when caribou eat mushrooms and validate the high nutritional value of this late-summer resource to caribou.


GPS video-camera collars provide researchers a new powerful tool for understanding animal behavior. This video highlights some of the other behavioral data that we can acquire from these animal-borne videos. Here, we see a female caribou with her newborn calf that is just days old, and although strong, we can tell it is still getting used to those long legs! Some of the data we might collect from this video can be pregnancy status, parturition (giving birth) success, date and location, and even how long the calf may have survived.


Additional animal behaviors are also documented with GPS video-camera collars. Here, we see caribou all grouped together in July, the time of year when insects become a constant threat to mental and physical energy reserves. In this video, we see individual behaviors of stomping their legs, standing around, not eating, and hanging their heads low to the ground as they wait out this stressful time of the year. Caribou aggregate to minimize the individual effects of insect harassment.  Information from videos like this will be used to better understand the tradeoffs caribou have to balance between summer feeding habits and insect harassment.