Hibernating bears can stop urinating for months. Their bodies conserve water and recycle urea instead of routinely excreting urine during the winter denning period.
This remarkable adaptation works alongside their reliance on stored fat. As fat is metabolized, it provides energy and metabolic water, while nitrogenous waste is redirected into a recycling system rather than simply lost. Bears may form a fecal plug in the colon as well, but that is a separate waste-related adaptation and does not change the answer to this question: the behavior they can stop is urination.
The bear’s winter state is sometimes called dormancy rather than “true” hibernation because its body temperature drops only modestly compared with that of many rodents. Studies of black bears in 2011 and brown bears in 2016 helped settle that terminology dispute. Bears can also avoid severe muscle loss by using urea-derived nitrogen to help make amino acids, linking waste removal directly to protein maintenance.