Black bears are solitary animals except for females (called sows) with cub families. They wander through home ranges of 10 to 250 square miles as snow recedes, plants sprout and berries open. Mating season peaks in May and June, but egg implantation is delayed until the fall when the sow is ready to den up for the winter. This allows the female to conserve fat reserves and energy during the growing season. If she doesn't gain enough weight before hibernation, her body can reabsorb the eggs for her own survival.