Dozing dormice

Snoozing their way through the cold...

I don't know about you but now the clocks have gone back and the nights are drawing in that bit earlier, I'd quite like to curl up and snooze until spring arrives.

It's mild now but autumn and winter can be harsh - frost and snow (or incessant rain) can make food hard to find for our wildlife. Many insects will be buried in the ground or hidden in crevices. Berries, colourful and juicy at the moment, don't last long (thank goodness for ivy and mistletoe). Keeping warm in dropping temperatures is a challenge, taking huge amounts of energy. For species like dormice, which rely on a range of foods that disappear as winter draws in, there is another option to scrabbling to survive. Hibernation!

Hibernation is essentially a deep sleep, where the body is able to conserve energy by reducing temperature, breathing, metabolic and heart rates. It is triggered by shortening day length and hormone changes within an animal that can last for days, weeks or months. It's not just mammals (dormice, hedgehogs and bats in the UK) that benefit from this slowing of systems; a similar strategy by insects is known as diapause and in reptiles it's called brumation.

Hibernation is no small feat. A hedgehog's heart rate can be between 200 and 280 beats per minute when they're awake but in hibernation it slows to just five beats per minute. Whilst asleep, the body is able to drop or raise the metabolic rate to compensate for a change in ambient temperature.

A dormouse (sandy-coloured small mammal with a long tail) stretching as it moves from one stem to another by Ian Pratt — Dormouse by Ian Pratt

With their honeyed colour, long tails, big eyes, rounded ears and penchant for sleeping, dormice are perhaps one of our most loved – if least seen – mammals. Dormice take first prize for being the UK's longest hibernating mammal. Depending on the weather, they can fall asleep as early as October and not wake again until early May; that's a lot of snoozing! But, then, their name gives this away, referring to the French dormir (to sleep) or dormeuse (a sleeper).

Dormice live in woodlands and spend almost all their time in trees and bushes, often right up in the canopy. They need a scrubby understorey, however, as this is where they build their nests. Their spring and summer nests lie abandoned when, after filling themselves with protein-rich hazelnuts during autumn, they head to the ground and snuggle into a ball of woven grass or bark covered with leaves or moss.

Two dormice curled up asleep, grasping their long tails over their bodies — Dormice by Cath Shellswell

Their secret to sleeping for such a long period is high body fat and a slow metabolism. In the run up to hibernation, dormice accumulate fat to help increase their bodyweight by up to 40%, weighing in at around 35-40g. During hibernation, they lose around 30% of their fat reserves so their first job on waking in spring is to find plenty of food to eat. Whilst asleep, their body temperature falls to that of the woodland and their heart rate and breathing slows down to around a tenth of the normal rate so they use barely any energy. Of course, they are vulnerable if a predator finds them; it can take quite some time to wake from a sleep that deep. It's one of the reasons that it's so important to keep dogs on leads in woodlands throughout the year and not just during bird breeding season.

Dormice are a protected species and you need a licence to survey for their presence but if you want to look for signs of them, look for nibbled nuts! If you find a hazelnut that’s got a perfectly round hole nibbled out of it, you may have found signs of dormouse activity; we’d love to hear from you if you do (you can send us a couple of good photos via our Wildlife Sightings form).