Fuzz: When Nature Breaks the Law

by Mary Roach

Food supply also affects hibernation. In a year of plentiful food, bears hibernate for shorter periods. For a bear that starts relying on human-sourced foods, every year is a plentiful year. Breck found that bears that foraged mostly urban areas hibernated a full month less than bears that foraged the natural landscape. Another concerning consequence of plentiful food is that reproduction rates rise. Black bear sows have a reproductive option called delayed implantation. Fertilized eggs become clusters of cells, called blastocysts, that loiter in the uterus over the summer. Whether they implant in it come fall—and how many of them do so—depends on the mother’s health and how well she’s been eating.