Where do the moose go? Solving a Moose Migration Mystery

For years, Refuge visitors and staff noticed that moose came into the mountain valleys in the eastern portion of the Arctic Refuge each fall, and disappeared again each spring. Where the moose spent the summer was a mystery. Meanwhile, the Vuntut Gwitchin Indians of Old Crow village in northern Canada had a mystery of their own. They knew that moose came to Old Crow Flats in late spring, but wondered where they disappeared to in the winters.

Refuge staff began working with the Vuntut Gwitchin when a new wildlife migration was discovered between the Arctic Refuge in Alaska, and the Indians' land in the Old Crow Flats area. This web page tells the story behind this discovery

Our story begins long before there was an international border between the United States and Canada. It was a time when people and wildlife moved freely across the land in response to the weather and the seasons.

moose study 2After the melting of the continental ice sheet some 10,000 years ago, the Old Crow Flats area became a huge melt-water lake. Eventually, the lake broke open, carving the ramparts of the Porcupine River. The thick deposit of silt that had settled on the lake bottom now contributed to the formation of rich soils across the Flats. In the Brooks Range mountains of Alaska, glaciers also retreated, leaving deep, protected valleys in their wake.

moose study 2bA system of thaw-lakes and wetlands developed on the emptied lake bottom, and a rich diversity of tundra, shrub, and forest vegetation became established. Along with the plants came a great variety of wildlife (muskrats, beaver, ducks, geese, swans, loons, and many other birds, caribou, bears, wolves, wolverines, and moose).

moose study 3At the same time, stands of willows began to grow in the empty valleys of the Brooks Range to the northwest.

In 1995, a study was initiated by Fran Mauer, a biologist with the Arctic Refuge, to try to find out where the moose in the eastern portion of the Refuge were going each summer.

The Arctic Refuge Moose Study Objectives were: 

  • Determine seasonal movements and distribution of moose 
  • Determine fidelity (whether they returned to the same place year after year) of individual moose to winter concentrations 
  • Assess relationship of moose concentrations to regional moose populations and human harvest 

moose study 10In late March and early April, 1995, 57 moose were captured and equipped with radio- collars. 15 moose were collared along each of three Refuge rivers: the Sheenjek (green circles), Coleen (yellow circles), and Firth (blue circles); and 12 were collared in the Kongakut River area (pink circles).

moose study 24Biologists immobilized the moose using standard dart/drug techniques. The moose were handled carefully, and all animals survived these capture activities.

moose study 8Each moose was examined and measured to find out how healthy it was. Blood, hair, and pellet samples were collected. A small hole-punched circle was removed from the ear for moose genetics (DNA) research at the University of Alaska. A colored ear tag was installed so the moose could be more easily spotted again in the field. A radio collar was placed around each animal's neck. These collars sent out radio signals that helped biologists relocate the moose. The radio-collars provided signals for up to 4 years.

moose study 9Because the moose move across a wide region of mountians and rivers, biologists flew in small airplanes to search for the animals in the study. This Cessna 185 was equipped with tracking antennas and a special radio receiver that picked up the sounds from each moose collar. The biologist and pilot used these signals to relocate each moose.

moose study 11By mid April, moose were moving from the Kongakut River area (most northern capture site), and some of the Sheenjek River moose had moved south down the Sheenjek River valley.

moose study 12In early May, many moose were moving to the south and east. Some had already arrived in Old Crow Flats.

moose study 13By the end of May, many moose had arrived in Old Crow Flats. Moose calves are born at about this time, so most young were born in Canada.

moose study 14During this study, 75% of the moose collared in Alaska migrated to Old Crow Flats. Most moose remained in Old Crow Flats during the summer.

moose study 15Old Crow Flats are ideal summer habitat for moose. There are many shallow lakes and ponds with aquatic vegetation (plants that grow in water), a common food item for moose during summer. In addition, there are several partially drained lake basins which have lots of aquatic vegetation as well as willows, another important food item for moose.

moose study 22According to data collected during this study, moose begin moving out of the Old Crow Flats in fall, and the movement to Alaska is completed by early winter.

moose study 16bUp to 196 kilometers (120 miles) separate summer and winter areas for some of the marked moose. This is the farthest that any moose are known to migrate in Alaska.

moose study 18The moose remain in the valleys of the Brooks Range throughout the winter.

Question: If Old Crow Flats is such good moose habitat, why don't they stay in the winter? 

Answer: Although the exact cause is not know, preliminary data suggest one reason may be that snow is drifted into the willows on the Flats (average depths exceeded 70 cm in 1997). In the Brooks Range valleys, the willows are protected from wind by the tall mountains, and the snow in the willows is not so deep (average depth was 50 cm in 1997). In other studies, snow depths greater than 70 cm have been found to significantly increase moose energy requirements. 

moose study 19Another possible cause of this unusually long seasonal migration may be the level of cold experienced on the Flats compared to that in the mountains. As air cools, the molecules slow down their movement, and become more closely packed together than they are in warmer air. This dense, cold air is therefore heavier, and sinks down to the lowest areas. Because of this, the coldest air slides down off the mountains, and pools in Old Crow Flats.

moose study 20Moose in the highter mountain valleys of Alaska may thus experience warmer winter temperatures, as well as having easier access to their winter food (willows). These factors may help calves to survive the winter, and allow cows to give birth to healthy young the following spring.

Summary: Because of the migratory nature of many species in the Arctic Refuge, we have come to recognize the shared international responsibility necessary to insure that our wild heritage is safeguarded for our use and enjoyment now, and for those who will follow us in the future. 

This information was adapted from:

Mauer, F.J. 1998. Moose Migration: Northeastern Alaska to northwestern Yukon Territory, Canada. Alces 34(1):75-81.