When a boar mates with a sow, his sperm fertilizes her ova to create a blastocyst, a hollow ball of cells, that floats freely within her uterus in a state of embryonic arrest for up to five months. The embryo or embryos within this blastocyst will develop no further until implanted in the sow's uterine wall later that fall. As summer progresses, the female roams about her home range, looking for choice foods. When acorns mature in September, bears begin a period of frenzied feeding that may last for up to 20 hours a day. Gorging on ripe acorns can result in an animal gaining as much as two pounds of fat per day.
Acorns are a critical food source for Ozark black bears.
When the acorn crop goes bust, pregnant sows enter hibernation in such poor shape their fetuses will not survive. Colder weather and reduced daylight combine to signal black bears that it's time to find a den. Just before a pregnant sow dens, the free- floating blastocyst finally implants itself in their uterine wall. Cubs are born while the female is still sleeping. And although a hibernating sow does not eat or drink, if she was in good physical shape when she entered her den she will produce enough milk to support her cubs until they emerge in springtime.