click on the image to view the mapped satellite data (1985-1990)

By the beginning of June, coinciding with the peak of calving, cottongrass emerges from the snow and offers much-needed fresh, green vegetation, high in digestible nitrogen. Calves are usually born in the Arctic National Wildlife Refuge along the Alaska coast of the Beaufort Sea. There is little variation in calving time for the herd as 80 per cent of calves are born within a week of June 2nd.

The period between calving and the end of June is critical to the cow and her calf. The ability to track fresh, green growth has a significant effect on calf growth and survival. Habitat choice and herd concentration during calving is a major focus of research.

This is also the highest period of mortality on the calves--50 percent of calf deaths occur in the month of June. Grizzly bears are the main predator on the calving grounds, with Golden Eagles and wolves sharing second place. Grizzlies are very effective predators for the first couple of weeks after calving. Soon after, the calves can usually outrun them.

By the beginning of July, a new element enters the life of the Herd: mosquitoes and parasitic flies such as nasal bots and warble flies. Harassment by insects greatly disrupts normal activity patterns of the Herd, reducing feeding time while increasing time spent running and walking.

The caribou have a couple of strategies for seeking relief from harassment. They can form tighter and tighter groups, thus lessening the harassment on any individual (a sort of insect swamping strategy) or they can seek out habitats that are cool or windy. Coastal habitats are the best escape as cool onshore winds from ice flows in the Beaufort Sea both lower temperature and increase wind.

Summer movement is largely on the coastal plain of Alaska. By the end of July, movement is directed toward the Richardson Mountains in the Yukon and the southern flank of the Brooks Range in Alaska. Freezing nights in early August reduce the insect populations and the large groups of caribou break into smaller groups that wander above treeline throughout August. Their diet begins the seasonal shift from willows and forbs to willows and lichens.