In the woods behind their home in Kinnelon, N.J., Mary and Steve Cobell see a lot of animals wander through: Squirrels, deer, coyotes and, increasingly, black bears.

“When we first moved in we didn’t see bears at all. As time passed you saw them more and more often,” said Ms. Cobell, who has lived with her husband in Kinnelon for 29 years. “My biggest fear is young kids will be out there doing kid stuff and might get hurt.”

Estimates...