Hedgehogs: Over the hedge

As their traditional habitats disappear, hedgehogs are in a prickly predicament. But in city gardens, their future looks rosier. Sanjida O'Connell finds out why

I once took a hedgehog home from rehab. It had lost its mother and been weaned in a wildlife rescue centre and I hoped it would live in my garden, shuffling around cutely, eating slugs. So I was a bit shocked when the owner of the rehab centre said it didn't like slugs and needed to be fed mashed banana, digestive biscuits and dog food. And I was even more put out when "my" hedgehog settled in and started frequenting the neighbours' gardens too. No doubt eating their dog food and avoiding slugs.

Hedgehogs typically range across around 10 gardens, covering a distance of 800 metres a night. "Hedge pigs", as they were once known, used to live in large numbers in the countryside, yet in recent years their population has dramatically declined. In some parts of East Anglia, numbers have fallen by 50 per cent. Although they don't seem to be doing well anywhere, hedgehog research throws up a surprising fact: urban populations are now doing better than their rural counterparts – though even in cities, population levels have declined by a third over the last 15 years. Dr Pat Morris, a zoologist formerly based at Royal Holloway, University of London, and an expert in British mammals, says, "Now in many big towns hedgehogs are extinct apart from areas that have cemeteries, playing fields and allotments."

Professor Steve Harris, a mammal expert from the University of Bristol, and his PhD student Claire Dowding, wanted to find out why. Parts of Bristol are blessed with cemeteries, playing fields, allotments and big gardens so Dowding was able to radio-track a number of hedgehogs. She fitted a transmitter to 30 adults a year and followed their nocturnal wanderings over the course of two years.

The results were mixed. Hedgehogs do better in cities because of the diversity of the gardens but, as Dr Morris points out, "It used to be the case that hedgehogs were numerous partly because people put out food for them and partly because we had large, overgrown gardens, but we've lost them and in their place we have whole rows of little houses with tiny, neat gardens." One concern of organisations such as The Wildlife Trusts is the loss of front gardens as people fill them in to park their cars on. While this is a problem for wildlife, it doesn't seem to affect hedgehogs, who prefer back gardens. However, a number of other issues are causing our hedgehogs problems.

Dowding monitored the levels of rodenticides in hedgehogs that had been killed on roads. Rodenticides such as warfarin and second-generation rodenticides, which are more toxic, were found in staggeringly high levels in a third of the animals. "We don't know how these chemicals affect hedgehogs," says Dowding, "It might be subtle – altering their ability to reproduce, for instance, or if they have a minor accident they might die because their blood won't clot. Or the dose may be lethal in many cases but we are not aware of it because we never find poisoned hedgehogs if they crawl away to die." Rodenticides can be bought over the counter in garden centres and hedgehogs may be ingesting them as they will eat the bait. They will also kill diseased rodents or scavenge the bodies. Surprisingly, slug pellets are not as big a problem as people once thought: a hedgehog would have to eat 2,800 poisoned slugs to ingest a lethal dose. However, as Professor Harris says, "they are full of other pesticides too, because hedgehogs eat so many different things and we're using so many chemicals in our gardens in very liberal amounts."

The situation in the countryside is even more dire. The main threat here is the change in farming methods, as over the last 40 years arable land has replaced grazing land.

Hedgehogs also face a threat from badgers. They are one of the few animals strong enough to prise open a hedgehog in spite of its spines; they also compete for the same food and as a badger eats five times as much as a hedgehog, it can be hard for them to co-exist with these large predators.

Dowding found a change in hedgehogs' pattern of behaviour. Normally the animals start to hibernate in November and emerge in April, but hers didn't begin to hibernate until January. "They're not going into hibernation properly and are active most of the winter," Professor Harris says. "Even if they're in their nests, they're pottering about, which is energetically expensive. What they want is to go into hibernation properly in good condition with high levels of fat and come out in good condition." The problem may well be due to climate change. As Professor Harris points out, "Everyone has their own pet theory for hedgehog decline. I suppose like most things it's likely to be multi-factorial, but one of the big problems you've got if you're hibernating in Britain is that you need hot summers and cold winters. Now we have warm winters and more unclear seasons, which are less predictable, and this disruption makes it very hard for hedgehogs."

Unless we go back to having large, untidy gardens, and reverse the situation in farming, hedgehogs are unlikely to increase significantly in numbers. However, there is one caveat. Scottish Natural Heritage announced that it was going to cull hedgehogs on the islands of Uist in the Hebrides because the animals, who were without natural predators, were running amok and eating wild birds' eggs, such as those of terns, and were decimating their populations. Professor Harris argued that it was perfectly possible to transfer the hedgehogs from the island to the mainland. "Hedgehogs are the ideal animal for translocation," he says, "they're generalists, so they don't have a specific food requirement, and they're not too territorial so you don't have to worry about finding them a territory."

To prove his point, Professor Harris, Dowding and another of his students released hedgehogs from Uist into Bristol. They compared their survival rates with hedgehogs released from wildlife centres, as well as a control group of animals. They discovered that if the Uist hedgehogs had a short period of time in captivity before being released, they did very well. " They needed to be kept for a short while to get over the stress of being caught and handled," says Professor Harris. Scottish Natural Heritage has finally taken on Professor Harris's recommendations and the Uist hedgehogs are no longer culled but released on the mainland. It's a small but significant victory: hedgehogs may be declining, but their numbers are being marginally boosted by their Scottish cousins.

How to encourage hedgehogs into your garden

*Allow some way for them to get in – a 10cm gap in the fence will do

*Have places where they can forage

*Have a small pond but ensure they are able to climb out if they fall in

*Don't use chemicals on your garden

*Discourage cats– they can kill the baby hedgehogs

*Have a compost heap – it's warm and provides them with invertebrates to eat

*Get a hedgehog box from www.organiccatalog.com. Alternatively you can build your own: for instructions on how, go to www.bbc.co.uk/nature/animals/wildbritain/gardenwildlife/myspace/content.shtml?11

*Feed them mealworms and commercial hedgehog food, available at www.spikesite.co.uk or www.greenwich-observatory.co.uk

'The New Hedgehog Book', by Pat Morris, Whittet Books, £12.99