Females with young are the most responsive to noise disturbance and the potential for harm from disturbance probably is greatest when it causes separation of females from their dependent young. Early abandonment, especially in the first year of nursing, probably results in starvation of the calf. In the first few days of the calf's life, the mother vigorously maintains contact with the calf. As the calf grows older the responsibility for maintaining the close association shifts to the calf, increasing the potential for separation during disturbance. Even temporary separations can be lethal, in that polar bears prey upon calves and take advantage of even brief separations from the normally attentive cow.
Calves especially are vulnerable to disturbance on terrestrial haulouts.
Large numbers of calves have been trampled to death during stampedes caused by human and natural disturbances of terrestrial haulouts. The potential for mortalities during stampedes appears to be less in the case of on-ice herds, which generally are smaller than herds on land. Natural Mortality Walruses are preyed upon by polar bears, killer whales, and man. The magnitude of natural mortality is unknown but is assumed to be low, given the population's low productivity. Eskimo hunters from St. Lawrence Island have described walruses becoming emaciated after becoming entrapped in heavy ice.