Hibernation and British mammals
Hibernation is the theme for the third programme in this year's series of Autumnwatch. In particular we're concentrating on Britain's only spiny mammal and quintessential hibernator, the hedgehog!
Hibernation differs from regular sleep in that it is a state of inactivity and decreased metabolism. Some animals like frogs and toads also go into a state of torpor, which is a state somewhere between sleep and full-blown hibernation which involves a significant drop in body temperature.
When a hedgehog begins hibernation its body temperature drops so low it almost matches the temperature outside. Similarly, the heart rate will slow down from 190 beats per minute to a mere 20. Respiration almost stops altogether, with just one breath being taken every few minutes. As a result of these physiological alterations, the hedgehog is able to conserve a massive amount of energy - surviving through the winter months on the fat reserves it is currently working hard to build up.
Dormice hibernate in an underground nest between October and April/May. Before they hibernate they fatten up to twice their normal size and they can lose up to half of their bodyweight during hibernation so have to feed up when they emerge. When they hibernate their heartbeat and breathing slow right down, and the body temperature drops to only a few degrees above freezing.
The 17 species of British bat all hibernate during the winter months when insects are scarce. They generally hibernate between November and April. Hibernation sites can be hollows in trees, roof spaces, caves, cellars or even purpose built bat boxes. During hibernation bats can take as few as five breaths per minute and their heartbeat can drop to about 20 beats per minute as the entire body slows down to save valuable energy. They can wake up for short periods to search for food and water and excrete waste, but this uses up a lot of energy.
Due to the hedgehog's nocturnal way of life, studying these elusive little mammals in their natural environment is difficult. The Autumnwatch team headed to St Tiggywinkles Wildlife Hospital in Buckinghamshire where hedgehogs of all ages, shapes and sizes are treated for a variety of ailments with the intention of being released back to their natural habitats.
At this time of year, hedgehogs in the wild are relentlessly foraging for food - conserving as much fat as possible for the cold months ahead when they'll head off to a suitable location to hibernate. The hedgehog's staple diet consists of beetles, caterpillars and earthworms and it's in the winter months that these little critters are increasingly hard to come by, hence the hedgehog's ability to hibernate through the barren months.
At Tiggywinkles, a hedgehog has to reach 600g in weight before it is considered for release and 20% of this weight must consist of fat reserves, which will ultimately 'run' the hedgehog's body during the months it spends hibernating. The prickly inpatients are fed on a diet of tinned dog food, dried cat biscuits (to aid in keeping the teeth sharp and clean) and water, a combination which suits their carnivorous appetites.
Read why Chris Packham thinks hibernation is amazing and find out more about hibernation and British mammals from these websites: