Wood mouse  (Apodemus sylvaticus)

Hibernate: a winter survival strategy characteristic of some mammals in which an animal's metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is 'diapause', a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.
Refection: in mammals, a process wherein food passes quickly through the gut and is re-eaten as it leaves the anus.
Ultrasound: sounds that are above the range of human hearing.

1. National Biodiversity Network Species Dictionary (May 2002)
   http://www.nhm.ac.uk/nbn
   
2. The Mammal Society wood mouse fact sheet (August 2002)
   http://www.abdn.ac.uk/mammal/woodmouse.shtml
   
3. Leach, M. (1990) Mice of the British Isles. Shire Natural History. Shire Publications Ltd, Aylesbury.
   
4. Macdonald, D. W. & Tattersall, F. T. (2001) Britain's mammals- the challenge for conservation. The Wildlife Conservation research Unit, Oxford University.
   www.wildcru.org