November update from Peter Shallcross

Even in the depths of December it’s amazing that some birds sing, brightening short winter days and bringing the promise of spring still months away. Robins, wrens and song thrushes are the easiest to hear but by the end of the day they will be joined by dunnocks and blackbirds.

The NASA is working out how humans could possibly be put into hibernation on the long voyage to Mars, but Andrew Graham has discovered how other mammals spend the winter:

‘Winter approaches and nature makes its preparations. While birds can migrate to warmer climes, other animals cannot, so need to hibernate. In the UK bats, hedgehogs and dormice hibernate. This allows them to get through the cold winter weather, when it would be impossible for them to find enough food to supply their energy needs. During the late summer months they need to feed up to increase their fat reserves and find or create a sheltered spot in which to hibernate. Then, as daylength shortens and the temperature drops, their metabolism slows. In a state of torpor or full hibernation, the metabolism may be only 5% of the normal rate, the body temperature much reduced and breathing almost stopped. This will slow the rate at which the fat reserves are expended.

Hedgehogs look for suitable places to create their nests – or hibernacula – under hedges, in piles of brushwood or under sheds. A hibernaculum is made of old dry leaves and grass and is densely constructed to wrap the animal in a protective layer to keep out the cold and hide it from predators.

In caves, the low temperature will never plunge to the depths outside on frosty nights. They can provide a place free from predation and so are a safe place for bats to hibernate. The caves in the old quarries at Chilmark provide a winter roost for at least six bat species and are so important that they have been protected as Sites of Special Scientific Interest.
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Hazel dormice make a nest in a ball of tightly woven dead leaves on the woodland floor, often under old, coppiced trees or hazel stools. These locations provide the dampness they need to ensure they do not dehydrate during hibernation.

Badgers do not hibernate but will be much less active in winter, spending much more time underground. Other mammals keep busy throughout the year and in so doing provide food for the animals and birds that prey upon them. At this time of year evidence of mole activity – molehills – can be particularly noticeable. This is because the wet weather drives the worms and grubs on which they feed closer to the surface. The mole’s permanent burrows are deeper down with excavated soil compacted into the tunnel walls. But when they follow their food upwards by creating new temporary tunnels closer to the surface, they push the spoil above ground to create the molehills.

Amphibians also hibernate. Frogs and newts will spend the winter months at the bottom of ponds, which makes them vulnerable if they are small and freeze up. Toads like to find somewhere sheltered and damp such as tree stumps, piles of brushwood and logs. It is therefore important not to disturb these piles during winter.’