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🦔 Hedgehog Hibernation Welfare

Hedgehog Hibernation Biology

Hedgehogs are one of only three UK mammals that truly hibernate (alongside bats and dormice). During hibernation, body temperature drops from approximately 35°C to close to ambient temperature (sometimes as low as 1–2°C), heart rate falls from 190 to 20 beats per minute, and breathing becomes slow and shallow. The hedgehog relies entirely on stored body fat reserves to survive the winter months.

Hibernation typically begins in October–November and ends in March–April, though timing varies with individual condition and local weather. Mild spells may trigger brief arousal — arousals are costly in terms of energy expenditure.

Welfare Risks During Hibernation

Insufficient Fat Reserves

The most critical welfare risk is entering hibernation underweight. Hedgehogs need to weigh at least 600g (ideally 700g+) before hibernating to survive winter on fat reserves alone. Hedgehogs under 500g entering hibernation will almost certainly die before spring. Juvenile hedgehogs born late in the year (from August onwards) may be too small to safely hibernate — these "autumn juveniles" are the primary casualties of harsh winters.

Hibernation Disturbance

Disturbing a hibernating hedgehog forces it to arouse — a process requiring significant energy expenditure. Repeated disturbance depletes fat reserves that cannot be replenished in winter, causing starvation. Common disturbance causes:

• Garden tidying disturbing leaf pile or compost heap nests
• Moving bonfire material without checking
• Garden renovation and construction work
• Domestic animal interference (particularly dogs)

Flooding and Temperature Extremes

Flooded hibernation sites drown hibernating hedgehogs. Extreme cold without adequate nest insulation can cause fatal hypothermia. Nests in exposed locations or areas prone to flooding carry higher welfare risks.

Identifying Hedgehogs Needing Help

Autumn Juveniles

Small hedgehogs (under 400g) found after mid-October are unlikely to survive hibernation and need intervention:

• Weigh any juvenile hedgehog found in October/November
• Under 450g: contact local hedgehog rescue or BHPS immediately
• 450–600g: supplementary feeding to support weight gain before hibernation
• Over 600g: safe to hibernate if otherwise healthy

Midwinter Activity

A hedgehog out in the open during winter (particularly during daylight) is in trouble. Reasons include:

• Starvation — insufficient fat reserves, using up brown adipose tissue reserves
• Nest disturbance forcing arousal
• Disease or injury
• Unusually warm weather triggering arousal without food availability

A hedgehog out in winter daylight should be collected (using thick gloves), placed in a box with a warm water bottle wrapped in a towel, and professional advice sought immediately.

Supporting Safe Hibernation

• Leave areas of leaf litter, log piles, and dense vegetation undisturbed from October–March
• Always check compost heaps before turning in autumn/winter
• Check bonfire material before lighting (always)
• Provide supplementary food in autumn to support weight gain: wet cat/dog food or hedgehog food, fresh water
• Consider a purpose-built hedgehog house in a quiet, sheltered garden location