Grand Teton National Park Report
Black bears have delayed implantation with fetal development and lactation energy demands during a period of maternal hibernation and starvation. Pregnant females in a state of diapause had about 23% greater fat depots than nonreproductive females going into hibernation. Fat provided 92% of the total energy for lactation and gestation. Rates of fat loss were 27% and protein loss 58% higher for reproductive females compared to non-reproductive females. The cost of winter reproduction to include gestation and lactation was 1432 kj/day to produce two cubs. While reproduction required elevated protein breakdown, the overall loss was relatively small, perhaps due to a short gestation period and urea recycling.
Harlow, Henry J.; Lohuis, Thomas; Tinker, Daniel B.; Grogan, Ronald G.; and Beck, Thomas D.I.
"Body Mass and Lipid Changes by Hibernating Reproductive and Nonreproductive Black Bears,"
University of Wyoming National Park Service Research Center Annual Report: Vol. 22
, Article 5.
Available at: https://repository.uwyo.edu/uwnpsrc_reports/vol22/iss1/5