page_title: Hibernation
section_title: Bears
hierarchical_section_title: Hibernation / Mammals / Bears
caption_attribution_description: English: Black Bear mother and cubs in den,, hibernating
context_page_description: Hibernation is a state of minimal activity and metabolic depression in endotherms. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most commonly occurs during winter months.
  Although traditionally reserved for "deep" hibernators such as rodents, the term has been redefined to include animals such as bears and is now applied based on active metabolic suppression rather than any absolute decline in body temperature. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilize similar mechanisms. The equivalent during the summer months is aestivation.
  Hibernation functions to conserve energy when sufficient food is unavailable. To achieve this energy saving, an endothermic animal decreases its metabolic rate and thereby its body temperature. Hibernation may last days, weeks, or months - depending on the species, ambient temperature, time of year, and the individual's body-condition. Before entering hibernation, animals need to store enough energy to last through the duration of their dormant period, possibly as long as an entire winter.
context_section_description: Historically there was a question of whether or not bears truly hibernate since they experience only a modest decline in body temperature (3–5 °C) compared with the much larger decreases (often 32 °C or more) seen in other hibernators. Many researchers thought that their deep sleep was not comparable with true, deep hibernation, but research in 2011 refuted this theory in captive black bears and again in 2016 in a study on brown bears.
  Hibernating bears are able to recycle their proteins and urine, allowing them to stop urinating for months and to avoid muscle atrophy. They stay hydrated with the metabolic fat that is produced in sufficient quantities that satisfy the water needs of the bear. They also do not eat or drink while hibernating and live off of their fat storage. Despite long-term inactivity and lack of food intake, hibernating bears are believed to maintain their bone mass and do not suffer from osteoporosis.  They also increase the availability of certain essential amino acids in the muscle, as well as regulate the transcription of a suite of genes that limit muscle wasting.
  In a study done by G. Edgar Folk, Jill M. Hunt and Mary A. Folk, they compared EKG of typical hibernators to 3 different bear species with respect to season, activity and dormancy, and found that the reduced relaxation (QT) interval of small hibernators was the same for the three bear species. They also found the QT interval changed for both typical hibernators and the bears from summer to winter. This 1977 study was one of the first evidences used to show that bears are hibernators.
  In a 2016 study done by wildlife Veterinarian and Associate professor at Inland Norway University of Applied Sciences, Alina L. Evans researched 14 brown bears over three winters. Their movement, heart rate (HR), heart rate variability (HRV), body temperature (Tb), physical activity, ambient temperature (TA), and snow depth were measured to identify the drivers of the start and end of hibernation for bears. This study built the first chronology of both ecological and physiological events from before the start to the end of hibernation in the field. This research found that bears would enter their den when snow arrived, and the TA dropped to 0 °C but even up to several weeks before they entered their den, Activity, HR, and Tb started to drop slowly. Their HRV dropped dramatically once in their den which indirectly suggests metabolic suppression being related to the bears hibernation.  Toward the end of hibernation and two months before arousal, the bear’s Tb rises, unrelated to HRV but rather driven by the TA. The HRV only increases around three weeks before arousal and the bears only leave their den once outside temperatures are at their lower critical temperature. These findings suggest that bears are thermoconforming and bear hibernation is driven by environmental cues, but arousal is driven by physiological cues.
caption: Black bear mother and cubs "denning"
exif: {}