By Richard Black
BBC environment correspondent
Otters are up, dormice are down, and rabbits are running rampant.
These are just three of the findings on British mammal populations released by the Mammal Society.
The rabbit population has gone up 10% in a decade
A decade ago, the Society produced its first nationwide survey; and it has just repeated the exercise, using information from professional conservationists and amateur enthusiasts.
The Society says it needs more volunteers to help track changes in these animals.
The rabbit has clearly become a dominant British mammal - along with humans and probably rats. The rabbit population is now estimated to be 40 million. It has risen by around 10% in 10 years.
But the most spectacular rise documented in this survey is that of the polecat.
Its population has grown from 15,000 to more than 60,000 in a decade - partly, according to Mammal Society Chairman Michael Woods, because gamekeepers are no longer suppressing its numbers.
"The number of gamekeepers has declined dramatically, and the polecat has responded by expanding its range," Mr Woods told BBC News.
Other species on the rise include:
"The story behind the otter's success is mainly the stopping of the really bad pesticides such as aldrin and dieldrin, which were commonly used in the 60s," explains Michael Woods.
- the badger; up from around 175,000 to 275,000
- seals; with the common seal up from 35,000 to around 50,000, and the grey seal from 93,000 to 130,000
- the otter; which shows a rise from around 7,000 to 12,000
"But then there's been a huge amount of effort in trying to make waterways better for otters, improving their habitat, providing them with more cover - and in some areas, particularly the eastern counties, there have been re-introductions as well."
The return of the otter is bad news for the mink, whose numbers have slid from 110,000 to 37,000.
They are being out-competed and sometimes out-fought by otters.
Having been introduced for fur farming, mink escaped in substantial numbers in the 1950s, establishing wild populations. Their decline is unlikely to be lamented.
The wild cat is, however, a cause for major concern, says the Mammal Society, with the population in the Scottish Highlands now thought to be only a few hundred.
The rise in the number of polecats has been spectacular
The dormouse is also fading - though the Society says it is not sure by how much.
In fact, it says, it needs many more volunteers to collect data on all mammals.
"We know so little about most British mammals - the bird world is far ahead of us," laments Michael Woods. "Birds are easier to watch - most mammals come out at night, and they're difficult to watch."
When bird charities do surveys, tens of thousands of people respond. The Mammal Society says it needs a volunteer army of comparable size.
"The more people we have got telling us what's happening to mammals out there, the better figures like this will be, and the sooner we will notice crashes like the otter suffered in the 60s," Michael Woods says.