The Great Caribou Migration

The calving ground is described as the heart of the herd, the point from which the caribou herd expands or contracts as seasonal and weather changes drive the animals on their migratory movements. In spring, pregnant cows instinctively head to this area as calving time approaches. Calves are typically born during a three-week period from late May to mid-June. Just two days after birth, they can travel over 10 miles per day. Within six weeks, antlers begin to grow.

The WAH calving ground is located in the Utukok River uplands, south of Wainwright and east of Cape Lisburne. The majority of caribou belonging to the WAH are born here. To a large degree, only maternal cows and often their calves from the previous year find their way to the calving ground. Non-maternal cows, some calves and nearly all bulls take a later, more leisurely trip, typically skirting to the south of the calving ground on their way to the Lisburne Peninsula. Later, they are joined by the cows and their new calves for post-calving aggregations.

From 2017 to 2019, a calf survival study took place in the WAH range. Each year, 70 plus radio-collars were put on caribou calves to determine how many calves survive their first year and to better understand the causes of death on the calving grounds.

Surviving until your first birthday as a caribou calf is no easy task. Over the three-year study the results varied more than expected. During the first year of the study on the calving grounds, predation was a contributing factor in calf mortality. Out of 78 collared calves, ten were killed by brown bears and three by golden eagles. Interestingly, the following two years of the study told a very different story; a single calf was killed by a brown bear in 2018 and there were no recorded predation events in 2019.

Mosquitoes begin to emerge in late June and early July. Caribou form massive groups, called aggregations, in attempts to shelter from the ceaseless swarming of blood-sucking insects. This small window of time is vital to biologists who are tasked with counting caribou as it is the only time the herd is grouped tightly enough for the whole herd to be counted. Using a small fixed-wing aircraft and a digital camera, they take an aerial census of the caribou in the WAH.Mosquitoes begin to emerge in late June and early July. Caribou form massive groups, called aggregations, in an attempt to shelter from mosquitoes and biting flies. This small window of time is vital to biologists who are tasked with counting caribou as it is the only time the herd is grouped tightly enough for the whole herd to be readily counted. Using a small fixed-wing aircraft and a digital camera, they conduct an aerial census of the caribou in the WAH.

In 2017, ADF&G replaced WWII-era black and white photographic cameras with new digital systems. The new system supports higher-quality photographs taken under a wide range of lighting conditions and a larger photographic footprint that allows more caribou to be photographed in a single shot. Digital imagery along with GPS information allows for automated alignment of the photos and eliminates the manual layout process used with print film. These improvements to the system result in better counts, which, in turn, equate to better information for herd management.

Twice a year, caribou journey between their summer and winter range, a process called migration. A variety of factors influence the timing and route of migration. Temperature and snow have the biggest and most consistent influence on migration. Snow can make caribou more migratory. One of the most interesting aspects of caribou migration is that caribou are constantly updating their decision to move throughout the fall. If caribou move to an area that’s warmer, they may slow down and pause their migration or, alternatively, speed up if conditions get colder and snowier.

In prior decades, their fall migration began in late summer. In the past few years, however, the fall migration was in late October and in early November. Hunters who rely on migration patterns for access were unable to harvest bulls before rutting season. One of the most iconic migration areas is Onion Portage, located on the banks of the Kobuk River. Its name originates from the Inupiaq word “Paatitaaq” meaning “wild onions” for the many wild onions found in this area. Hunters use the caribou’s seasonal migration to their advantage. When the caribou arrive, so do the hunters. Archaeological records indicate it has been this way for at least 10,000 years.

For decades, ADF&G and NPS biologists along with students from nearby communities visited the Kobuk River each fall to deploy radio collars on caribou. As caribou swam the river, a boat drove alongside a chosen group, then biologists and students held on to an adult caribou, placed a collar, took a blood sample, and recorded its body condition. Collaring caribou allows biologists to locate caribou, follow their movement, and track areas of preferred use.

As caribou fall migrations have shifted, the caribou collaring program at Onion Portage has become much less reliable. Because there is no other reliable location for boat captures, helicopter collaring is becoming an alternative solution.  

Winter blankets the tundra with snow. To the untrained eye, it can appear there is minimal food for the caribou. Lichen, their primary winter food, can be buried beneath feet of snow. Caribou gravitate towards windy mountaintops, ridges, and other windblown areas in search of shallow or snow-free terrain. Their crescent-shaped hooves allow them to crater or dig into snow to obtain lichen.

Their winter range spans over vast, remote areas. Communities who reside within or near the WAH winter range have the opportunity to harvest these animals. A popular area for Seward Peninsula residents to hunt for caribou in late winter and early spring is Serpentine Hot Springs. Subsistence hunters visit this area to hunt and enjoy the thermal water’s healing properties.