The ideal minimum weight to give a hog a chance of successful hibernation is 650g. This article by Dr Toni Bunnell in response to the MailOnLine’s recent story about whether or not we should feed hedgehogs in the run-up to hibernation makes very interesting reading. Dr. Bunnell is a hedgehog rescuer/rehabilitator and has been collecting data for over 27 years.
HEDGEHOGS & HIBERNATION: THE FACTS by Dr Toni Bunnell
The West European Hedgehog (Erinaceus europaeus), that exists in the UK, is in a state of critical endangerment. It is not merely the catastrophic decline in numbers over the past few decades, but the rate of decline, that is giving cause for concern. The reasons cited include the decrease in available food, the invertebrate population having fallen by 45% in the past 35 years. It is well established that, in order to survive a spell in hibernation, a hedgehog needs to achieve a minimum prehibernation weight and percentage of body fat, in particular brown fat that is slow to metabolise. Analysis of some of the data I have collected, during the 27 years I have spent running York Hedgehog Rescue, revealed that, in order to have a realistic prospect of surviving hibernation in the UK, a hedgehog needs to be a minimum of 650g, with a rounded end (sphere-shaped).That is, a satisfactory weight for its size. As invertebrate food becomes ever scarcer, it is more and more important for people to support their local hedgehog population by supplying food such as cat biscuits (e.g. IAMS), but not peanuts or dried mealworms. In the UK hedgehogs typically hibernate between September and April. However, sudden falls in temperature have been known to trigger short spells of hibernation during the summer months (Bunnell, personal observation, plus countless reported incidents from other rescues in the UK). It is important to remember that it is not necessary for hedgehogs in the UK to hibernate in order to ensure their survival. Indeed, on the North Island of New Zealand, where winter temperatures are significantly higher than in the UK, the same species of hedgehog does not hibernate at all. Hibernation is purely a product of environmental circumstances. The single biggest trigger for hibernation is a sudden fall in temperature and not, as often erroneously proposed, the lack of availability of food. I have repeatedly come across statements from people saying that they are reducing the amount of food given to hedgehogs in their care, in an attempt to force them to hibernate. This is foolhardy and entirely wrong. It will not trigger hibernation but merely starve the hedgehog concerned, thus preventing it from reaching a weight that would allow it to survive subsequent periods of hibernation necessitated by a drop in temperature. In addition, once the onset of hibernation has been triggered, hedgehogs do not hibernate continuously; rather they exhibit a behaviour known as periodic arousal. They emerge from hibernation intermittently, for varying amounts of time, during which they forage and eat. This allows them to replenish their reserves. They will then lapse into hibernation once more, until triggered to emerge again. This process can be repeated several times during the course of the winter months. A sample of hibernation data that I have collected over the past 27 years is given in the chapter on hibernation in my book: Rescuing the Disappearing Hedgehog: https://tonibunnell.com/…/rescuing-the-disappearing-hedgeh…/ Various factors come into play when determining the time of onset of hibernation for individual hedgehogs. These include the weight/size relationship, age of the animal, and temperature change. Nowhere in this equation does food availability feature regarding the onset of hibernation of hedgehogs. In conclusion: THERE IS NO BENEFIT WHATSOEVER OF WITHDRAWING FOOD. IF YOU WANT TO HELP HEDGEHOGS IN THE UK, SUPPLEMENTARY FEED THEM ALL THE YEAR ROUND. Thank you for reading this. Please share far and wide.