The 2 to 3 week long calving season is the most critical period in the annual cycle of the caribou. The pregnant cows reach the calving grounds after the 2 month long migration. They arrive thin and gaunt having with much of their energy going into the unborn calf as well as the long journey. The optimal calving grounds are the disputed 1002 lands. If the cows reach this location the calf survival rate is usually high. This is because the vegatation in this area is especially nutritious and the herd is relatively safe from predators. They are very sensitive to any disturbances during this time. Two key factors that go into the equation on the spine is a "green-ness value" which represents the vegatation quality and a predator risk value. The more concentrated the herd is when it calves, the lower the risk is to predators. Predators during calving are grizzly bears and 1st year golden eagles. Wolves are stuck back in the foothills where they can dig dens for their young (the calving grounds are on permafrost).  By the time they can venture out to hunt caribou, the calves can run.