Morris (1984) hedgehog hibernation minimum body weight

Title: An estimate of the minimum body weight necessary for hedgehogs (Erinaceus europaeus) to survive hibernation,  Notes from the Mammal Society 48; 291-294. 1984

Authors: P. Morris

Country: UK

Background to study

British hedgehogs need to attain enough fat reserves to enable them to survive overwinter hibernation, however, current predictions are based on larger European conspecifics.  This study investigated the minimum body weight required for hedgehogs to survive overwinter. 

Method

• Weight data obtained during March or April from 105 hedgehogs, 49 live animals captured during fieldwork and 56 individuals that had died either during hibernation or had been killed by gamekeepers or road traffic .
• Estimates of minimum body weight prior to hibernation were calculated by taking the mean weight loss derived from published records of hibernating mammals of similar size from the UK (25%) and an inflated value (40%) derived from spring weights of post-hibernating hedgehogs in laboratory conditions.
• Distribution of estimated pre-hibernation weight was used to derive minimum body weight and this was assessed against the distribution of weights obtained from 98 individuals captured between October and November to gauge the extent of overwinter mortality expected due to insufficient fat reserves.

Key results

• Based on a 25% loss of body weight overwinter, hedgehogs weighing less than 400g are unlikely to survive hibernation but, to account for severity in environmental conditions overwinter, the minimum weight for survival during hibernation is estimated to be 450g. At a loss of 40% body weight, the minimum threshold weight to ensure overwinter survival increases to 550g.
• Hedgehogs with pre-hibernation weights of 1500g are not uncommon and these individuals are unlikely to lose as much body weight as smaller individuals during hibernation.
• Hedgehogs can attain a weight of over 500g in 8-10 weeks and thus those born later in the season (after September) are unlikely to survive hibernation and are at greatest risk of overwinter mortality.
• There is a high incidence of hedgehogs observed in autumn that were below the estimated threshold weight, suggesting that insufficent fat reserves are a major factor contributing to hedgehog mortality.

Key messages to landowners and managers derived from these results

• Individuals weighing less than 450g after September are ‘at risk’ to overwinter mortality and intervention through supplementary feeding may decrease this risk.