Britain's favourite prickly character suffers a sharp and mysterious decline in numbers

Whether they are called Mrs Tiggywinkle or Sonic, hedgehogs have always had a strong hold on the nation's affections. But according to a new study, the creatures' days in our gardens could be numbered.

The Mammals Trust UK warned that hedgehog numbers may be in serious decline, as the animals become victims of a combination of a destruction of habitat, drier summers and increased road traffic. Figures published yesterday by the Trust suggest numbers across Britain may have declined by as much as 30 per cent over the past four years.

"It is of great concern to see that the decline in hedgehog numbers is continuing," said Jill Nelson, chief executive of the Trust. She urged the public to help the Trust in understanding the true picture by taking part in their annual survey of mammals, which starts tomorrow. It also warned that the decline might have implications for other species with similar needs.

The apparent reduction comes in spite of intensive campaigns by both the Government and wildlife groups to stop drivers running over hedgehogs and to rescue them from garden bonfires, particularly around 5 November, when mounds of leaves provide attractive places for hibernation.

The Trust's Mammals on Roads survey for 2004, which measures the number of mammals seen on British roads, shows that the number of hedgehogs declined from 1.67 per 100 kilometres in 2001, the first year of the survey, to 1.17 last year; a fall of around 30 per cent. The decline was most marked in eastern England, where figures fell from 2.6 in 2001 to 2.1 last year. Gross numbers show that in 2001, 2,569 hedgehogs were seen on 128,000km, while in 2004, 109,000km driven led to 930 sightings.

Although the Trust cautioned that it was too early to tell how much of a long-term trend was indicated by the results, the overall numbers were lower than a similar survey undertaken in the early 1990s.

Dr Paul Bright of Royal Holloway college, University of London, who analysed the results, said: "It's important to continue to monitor hedgehogs and determine why their numbers are changing, not only to ensure we safeguard this species for the future, but also because if the hedgehog is declining, so will many other species with similar needs. Mammals on Roads is currently the only survey able to monitor hedgehog numbers on a national scale."

Among the factors believed to be responsible for the decline are the increased intensification of agriculture, which has led to a reduction in the hedgerows, brambles and thickets that are the preferred natural habitat of the hedgehog. Despite the fact that gardeners have always encouraged hedgehogs because of their appetite for slugs and snails, the increase in "designer" gardens, where paving and decking have replaced lawns and shrubberies, has also affected their habitats. Drier summers, which reduce the amount of moisture and slugs may also be responsible.

Many hedgehogs also die from eating slugs which have consumed slug pellets put down by gardeners. Fay Vass, of the British Hedgehog Preservation Society, warned that some pellets which were marketed as being "wildlife friendly" still contained the chemical metaldehyde, which is dangerous to hedgehogs; the society has lodged complaints with advertising standards authorities about one particular company.

She said: "We are also very concerned about the decline. We believe increas-ed use of pesticides in agriculture and the increase in road use are also responsible for this situation." The society produces information packs for those wanting to encourage hedgehogs in their gardens; this includes leaving some areas untended to provide nesting places, as well as the right kind of food to leave out, such as most meat-based leftovers or cat food.

The Mammal Trust survey is based on reports by members of the public, who are asked to keep a log of all sightings of mammals, both alive and dead on single carriageway roads on journeys of more than 20 miles during July, August and September.

Respondents to the survey logged sightings of 24 species of wild mammals during 2004, including five of the six species of deer and seven carnivores – stoat, weasel, polecat, otter, badger, mink and fox.

Hedgehog habits

* Hedgehogs have up to 500 spines, but only on their backs. The rest is fur

* They are nocturnal and hibernate from November to March

* The hedgehog protects itself by rolling into a ball, so its spikes stand out in all directions

* In the wild, they sleep in a ball or stretched out. They prefer to nest under rocks, roots or in leaves

* Hedgehog fleas prefer hedgehogs and will not live on cats, dogs or humans

* Hedgehogs sneeze, snort and click. When frightened they squeal, and when happy they purr

* Babies, white when first born, are called hoglets

* Although they eat insects, they will also eat mice, frogs, small birds, and worms. They also steal birds' eggs from nests

* Many people leave food for hedgehogs in the garden – they like meat scraps or pet foods, but never fish; they should never be fed bread and milk – it gives them diarrhoea