What happens to a hedgehog’s body during hibernation?
As the weather cools further in Cornwall, hedgehogs begin preparing for one of the toughest challenges of their lives: winter hibernation¹. For hedgehogs, hibernation isn’t just a long nap – it’s a drastic physiological transformation that allows them to survive months without eating or moving far from their nest¹.
Preparing for winter: fattening up
Before hibernation begins, hedgehogs spend weeks feeding as much as possible². Their natural diet of beetles, worms and other invertebrates becomes scarcer as temperatures drop, so they gorge on what they can find to build up fat reserves². These fat stores are critical – without enough energy in their bodies, a hedgehog is unlikely to survive the winter². Experts suggest a hedgehog should weigh around 600 g by early winter to have the best chance of survival³.
Hedgehogs store two main types of fat: white fat, spread through their body to fuel long-term energy needs, and brown fat, which is held in special pockets and used for the intense bursts of heat needed when waking up from deep hibernation⁴.
Entering torpor: metabolism slowdown
Once in their nest – often made from leaves and vegetation and called a hibernaculum – a hedgehog begins hibernation by entering a state known as torpor¹. This is far more extreme than ordinary sleep¹.
During torpor:
Body temperature drops dramatically, from around 35 °C to close to the surrounding soil temperature, often below 10 °C⁵
Heart rate slows massively, from roughly 190–280 beats per minute when active to as few as about 14 beats per minute⁵
Breathing becomes shallow and infrequent, sometimes just a few breaths every few minutes¹
Metabolic rate falls by about 95%, meaning their bodies use far less energy and can rely almost entirely on stored fat⁵
These changes turn a warm-blooded mammal into something resembling a cold-blooded animal in terms of energy use, allowing them to endure months of little to no food⁶.
Waking up: periodic arousals
Hibernation isn’t a single, unbroken sleep. Hedgehogs periodically arouse – sometimes every week or two – temporarily raising their body temperature and metabolism before returning to torpor⁵. The exact reason for these arousals isn’t fully understood, but they likely help the body maintain organ function and repair cells⁵.
These brief wakeful moments are energetically expensive, so unnecessary disturbances in winter (such as gardeners clearing leaf piles too early) can use up precious fat stores, putting the hedgehog at risk⁷.
Emerging in spring
When temperatures rise and daylight increases, the hedgehog’s body begins the long process of returning to normal physiological function¹. They emerge from their nests hungry and dehydrated, having lost a significant amount of weight – often 20–30% of their pre-hibernation body mass⁸. Finding food quickly is vital to survival as spring begins¹.
Top 5 ways to help hedgehogs during hibernation in Cornwall
Leave natural shelter in gardens and hedgerows
Hedgehogs hibernate in leaf piles, compost heaps, log stacks and dense hedgerows¹. In rural Cornish villages, avoid cutting back hedges or clearing garden debris during winter wherever possible⁷.Provide a sheltered hedgehog house
A well-placed hedgehog house can offer vital protection, especially in exposed coastal gardens⁷. Position it in a quiet, dry spot and cover it with leaves or brushwood for insulation⁷.Avoid disturbing hibernating hedgehogs
Hibernation isn’t a deep sleep. Waking a hedgehog uses up precious fat reserves and can be life-threatening¹,⁷. Always check carefully before bonfires, garden clearance or hedge cutting⁷.Offer food in autumn and early spring
Putting out meat-based hedgehog food or plain cat food helps hedgehogs build and restore energy reserves²,⁷. Fresh water should be available year-round⁷. Never feed milk or bread, as these can cause serious health problems¹.Create hedgehog highways between gardens
Small gaps (around 13 × 13 cm) at the base of fences allow hedgehogs to move freely between gardens, supporting healthy populations across villages, towns and coastal communities⁷.
Read more
Sources
RSPCA – Hedgehog hibernation and winter behaviour
RSPCA – Hedgehog diet and seasonal feeding
St Tiggywinkles Wildlife Hospital – Hedgehog weights and winter survival
Home & Roost – Hedgehog fat reserves and hibernation biology
Biology Insights – Physiological changes during hedgehog hibernation
Hedgehog Rescue UK – Energy use and torpor in hedgehogs
Hedgehog Street – Helping hedgehogs during hibernation
Wildlife ecology and rehabilitation sources on post-hibernation weight loss