One individual in the city centre, however, is very much awake, intent on getting somewhere, and in an old watermill spanning the River Itchen which flows through the city. The individual is suddenly caught by infra- red light and a video camera: a wild otter.
This grainy still is dramatic proof of just how substantial is the otter's comeback. An animal that was extinct in most of England and much of Britain 20 years ago is steadily returning to its former haunts, and swimming right through the middle of conurbations to do so.
Otters have been spotted or traced swimming through Stoke-on-Trent, Reading, Exeter, Glasgow and other urban centres besides Winchester and are present on 28 rivers which flow through towns and cities, according to the most comprehensive account of otter distribution to date, published today by the Wildlife Trusts.
The report, Splash Back, shows that because of improvements in water quality and efforts to restore waterside habitats, the otter's gradual recovery has sped up in the past five years. The animals are now recolonising many areas from which they so dramatically disappeared in the late 1950s and 1960s.
The report says otters are at their most numerous in Devon, which has always been their English stronghold, in Scotland and in parts of Wales, but they are coming back strongly in East Anglia and in Northumberland - they have been seen three miles from Newcastle upon Tyne. They are spreading from Wales into the Severn and Trent catchment areas and can be found on the edge of Birmingham. Populations are recovering in Wiltshire, Somerset and Hampshire, but Surrey and Kent are largely still awaiting their return.
But the report also sounds a warning that otters face new and potentially deadly threats, in the form of pollution, habitat loss and road traffic.
Of particular concern is a family of chemicals used in sheep dips, synthetic pyrethroids (SPs). SPs wipe out aquatic life at the base of the food chain, depriving fish of insect food and leaving otters short of prey: one teaspoon of SP dip/, the report says, could kill the insects in an area the size of an Olympic swimming pool. The Wildlife Trusts are calling for SPs to be withdrawn from sale pending further research.
Loss of habitat is a continuing problem, but death on the roads is also a big threat to otters. Recent research has shown that road traffic kills 60 per cent of the otters that die violently in the UK, so the trusts are calling for measures such as otter underpasses and fencing to become mandatory on all new road, river engineering and rail projects.
"Many animals are very careful about entering a dark tunnel," said Tim Sykes, the Environment Agency conservationist for Hampshire who is in charge of the otter monitoring at the Winchester mill. "Sometimes they jump out and walk along the bank. It's a classic problem elsewhere in the country with roads. Otters don't like swimming through a culvert under a road. They would rather walk up the bank and over it. That's when they get killed by traffic."
The otter pictured scurrying through the Winchester mill had just swum along an open section of the river past footpaths, pubs, private gardens and major roads, until its movement activated the camera. "Maybe they're not as shy as we used to think," Mr Sykes said. "They're just extremely elusive."
But his study of otters on the Itchen is using something much more ambitious than random photography: DNA fingerprinting of individual otters. Volunteers pick up the otter droppings, or spraints, early in the morning while they are still fresh, and they are sent to the University of Aberdeen.
It is the first such project of its type in the world, Mr Sykes said. "Till recently we had to rely on their tracks and signs as clues to their expanding distribution," he said. "Using DNA analysis is like moving from the Wright brothers to Neil Armstrong. We should be able to build up a detailed picture of the otter population."
'Splash Back. The Return of the Otter' is published by the Wildlife Trusts, The Green, Witham Park, Lincoln LN5 7JR.Reuse content