Spring Migration - Caribou Activities

March and April

In late March, winter still grips the north but caribou instinctively know that spring is near. Females and their calves of the previous summer begin moving north first. Soon, however, male calves start falling behind, followed later by female calves and then many of the non-pregnant cows. By the time spring migration is in full swing in late April, pregnant cows are far in the lead and bulls are only just beginning to leave the wintering areas.

Deep snows can delay spring migration, but the drive to return to the calving grounds draws caribou ever northward. The caribou often follow rivers, where snow is harder packed and easier to walk on, or they may travel on windswept ridges. Caribou also follow in each other's trails. There is no "leader" to the migration. Older, more experienced cows are usually at the front, but leadership changes frequently because all of the caribou know instinctively where to go, and because no single animal can continue the tiring work to break trail for long. Because of the burdens of plowing through deep snow, spring migration trails are usually more concentrated than during fall. Not until they reach the shallower and harder packed snow of the coastal plain do the northward migrating caribou begin to fan out.

Snow is usually shallower and melts earlier on the coastal plain in the northern Yukon than in other nearby areas. Therefore, Porcupine Herd cows that have wintered in Canada and south of the Brooks Range in Alaska migrate first to the northern Yukon before following the coastal plain west to favored calving grounds in the Arctic Refuge.