Once upon a time, black bears were symbols of wild country and wilderness. Today I wouldn't doubt a bear sighting in almost any county in Pennsylvania. Count Pennsylvania's black bears as another wildlife management success story.

Bears reproduce slowly, so it's no surprise that the population has taken decades to build. Litter size ranges from one to four, with twins being typical. But adult females breed only every two or three years, giving them time for extended care of the cubs.

Furthermore, juveniles grow slowly and often don't reach reproductive age until they are 3 to 5 years old. Periodic food shortages caused by poor mast years and stress from human-bear conflicts can cause females to skip breeding occasionally.

Black bears will soon retire to their winter dens, and many healthy adult females will be pregnant. Breeding occurred back in May or June, but the embryo(s) did not immediately implant on the uterine wall.

Instead, development was arrested in a process called "delayed implantation." If females are healthy as they enter the winter den, the embryos implant and development begins. Cubs are born in the winter den and weigh only 8 to 10 ounces.

Black bear cubs open their eyes at about four weeks of age. They leave the den when about 4 months old and stay with their mother until their second summer. By that time, she is usually pregnant with her next litter.

Survival of young bears is high while with their mother, but after gaining independence, life becomes more difficult. They disperse to unfamiliar areas, struggle to find food, and often encounter aggressive adult males. Many young bears fail to survive the sub-adult period.

Pennsylvania black bears grow to 250 to 400 pounds in adulthood, and there are usually a few 600-pounders taken each bear season.