Hedgehogs are familiar sights in many gardens across Europe, Asia, and Africa. These mammals are among the few true hibernators, a profound physiological transformation where bodily functions dramatically slow down. This natural process enables hedgehogs to endure periods when resources become scarce, highlighting their remarkable resilience.
The Purpose of Hibernation
Hedgehogs hibernate as a survival strategy to navigate harsh environmental conditions, especially when food sources become scarce and temperatures drop. During colder months, their insect and invertebrate diet becomes difficult to find, making active foraging unsustainable. Hibernation allows them to conserve energy that would otherwise be spent maintaining body temperature and searching for food.
The metabolic advantages of hibernation are significant, enabling hedgehogs to survive for extended periods without consuming food. An active hedgehog might deplete its fat reserves in 16 hours, but in hibernation, these same reserves can sustain the animal for approximately 120 days. This dramatic reduction in energy expenditure is essential for their survival through winter. While commonly associated with winter, hibernation can also be triggered by any prolonged period of food shortage, underscoring its role as a flexible survival mechanism.
Preparing for the Long Sleep
Before their winter slumber, hedgehogs engage in preparatory behaviors. They accumulate substantial fat reserves through increased feeding during autumn. These fat stores serve as the primary fuel source to sustain their metabolism throughout hibernation. Hedgehogs need to reach a body weight over 600 grams to successfully hibernate.
Hedgehogs also construct a secure, insulated nest, known as a hibernaculum. These nests are typically built in sheltered, dry locations like under hedges, log piles, compost heaps, or beneath sheds. They weave dry leaves, grass, and other vegetation into a compact, dome-shaped structure with thick walls, providing protection from predators and insulating against temperature fluctuations.
Life in Slow Motion
During hibernation, a hedgehog’s body undergoes profound metabolic depression. Its normal body temperature, typically 35°C (95°F), plummets to within a few degrees of ambient temperature, often reaching 7-10°C (45-50°F). This drop is accompanied by a drastic reduction in heart rate, slowing from 190-280 beats per minute to as low as 14. Breathing becomes incredibly shallow and infrequent, decreasing from 25-50 breaths per minute to just 1-3, sometimes with brief cessations.
The hedgehog’s metabolism slows by approximately 95% during this state, allowing it to rely almost entirely on its stored fat reserves for energy. This state is not continuous; hedgehogs periodically experience brief arousal cycles, typically every few weeks. During these arousals, their body temperature and metabolic rate temporarily increase, enabling them to perform basic physiological functions before returning to torpor. While energetically expensive, these periodic awakenings are believed to be necessary for cellular repair and maintaining organ function.
Waking Up and Beyond
Emerging from hibernation involves a gradual, energetically demanding return to normal physiological functions. Arousing from torpor requires the hedgehog to rapidly increase its body temperature, fueled by specialized brown adipose tissue. This rewarming can take several hours, during which heart rate and circulation progressively return to active levels.
Once fully awake, a hedgehog’s immediate needs are to find food and water to replenish the significant weight lost during hibernation, which can range from 25% to 40% of its pre-hibernation body mass. The post-hibernation period presents challenges as natural food sources may still be scarce in early spring. Shortly after emerging, hedgehogs typically enter their reproductive cycle, marking the start of a new active season.