Unlike most mammals, hedgehogs lack the insulation of a warm fur coat. And keeping the body warm requires a lot of energy, so as it goes into winter and it gets ready for hibernation, the hedgehog's temperature drops from the normal 35ºC to that of its surroundings: 10ºC or less.
The hedgehog's winter nest, known as a 'hibernaculum', is made of grass and especially of leaves, which are weatherproof and long-lasting. The hedgehog brings leaves to the nesting site in its mouth, a few at a time. It makes a pile, adding new leaves to the centre; they are held in place by the surrounding support of twigs, brambles, brushwood, etc. It then burrows inside and turns round and round, packing the leaves flat and ending up with a warm chamber with walls up to 10cm thick.
Next winter, the hedgehog will make a new nest, even if the old one is still usable.
