When do hedgehogs hibernate in the UK?

When do hedgehogs hibernate?

The British Hedgehog Preservation Society (BHPS) puts the start at November or December, and sometimes as late as January. The RSPCA and the RHS say October or November. They're both right, because hibernation doesn't start on a date. It starts when the temperature around the hedgehog drops and stays down, so a mild autumn keeps them up for longer.

Before that, they spend autumn eating as much as they can. A hedgehog goes into winter living on the fat it's put on, and the ones born late in the year have the least time to put it on.

A rough hedgehog year looks like this:

• October: feeding hard. Late litters are still out, and some of the young ones are too small to make it through winter.
• November and December: most settle into a nest for the winter.
• January and February: hibernating, with short wake-ups, more often in mild spells.
• March and April: waking up, thin and hungry.

When do hedgehogs wake up?

Hibernation usually ends between mid-March and early April, says the BHPS. The RHS puts it at March or April. They come out hungry, at a time of year when there isn't much to eat, so food and a shallow dish of water in the garden make a real difference then.

Hedgehog Street, the campaign run by the BHPS and People's Trust for Endangered Species, points out that a hedgehog can wake early on a mild day, have a quick look for food and go back to sleep. So one pottering about on a warm night in February isn't necessarily a problem.

What happens to a hedgehog in hibernation?

It isn't really sleep. Hedgehog Street calls it torpor: the hedgehog lets its body cool to match its surroundings. According to the BHPS, its body temperature falls from about 35°C to 10°C or less, and its heart slows from around 190 beats a minute to about 20.

The best temperature for a hibernating hedgehog is about 4°C. At 10°C it burns through its fat twice as fast, so a mild winter isn't necessarily a kinder one.

Most hedgehogs wake up several times over the winter. These spells last a day or two, and they rarely leave the nest.

How heavy does a hedgehog need to be to hibernate?

The BHPS says a healthy young hedgehog that weighs over 450 g (about 1 lb) can survive hibernation. From the end of October, youngsters under 450 g may need rescuing, depending on the weather.

That's the reason for all the autumn appeals about small hedgehogs. A late litter born in September has only a few weeks to get to a safe weight.

Is it bad to see a hedgehog out in the day in winter?

In autumn and winter, usually yes. The BHPS is blunt about it: a hedgehog out in the day at that time of year is behaving oddly, and it may be only days from death. Call the BHPS on 01584 890 801 to find a rehabilitator near you, and if it's hurt, get it to a vet or a hedgehog rescue quickly.

Summer is different. A mother hedgehog moving with purpose in daylight, carrying grass or leaves, is probably just collecting nesting material. Hedgehog Street's advice for that time of year is to watch for one that's wobbly, lethargic or has flies around it.

There's one more case. If a hedgehog visits your garden regularly, only comes at night and looks lively, the BHPS says it can stay in the wild, as long as you're willing to feed it every night.

How to help hedgehogs this winter

• Leave leaf piles, log piles and the space under the shed alone until spring. Hedgehog Street asks people not to clear them, or open up a hedgehog house, over winter, because there may be a hedgehog asleep inside.
• A hedgehog house in a quiet, shady corner gives one somewhere safe to nest. The RHS suggests a design with a tunnel entrance or a baffle inside to keep predators out.
• Build a bonfire on the day you light it, or move the pile first. Hedgehogs tend to crawl into the middle and the bottom two feet, so lift it section by section with a pole or broom to check (never a fork), and light it from one side so anything inside can get out.
• Turn compost with care, because one push of a fork can kill a hedgehog. The BHPS suggests October or November as the safest time to spread a heap.
• Look through long grass before you strim. The RHS says strimmers are one of the biggest causes of hedgehog deaths and injuries.
• Put out meaty cat or dog food, or dry cat or kitten biscuits, with a shallow dish of water. Never milk, as hedgehogs are lactose intolerant, and don't bother with bread, which is almost worthless to them.
• Skip the slug pellets. The BHPS asks people not to use them at all.
• Cut a hole 13 cm by 13 cm at the bottom of your fence. That's big enough for any hedgehog, and they need the room: they travel about a mile a night looking for food and mates.

Why it matters

Hedgehogs are in trouble. The State of Britain's Hedgehogs report from 2022 found numbers had fallen by between a third and three-quarters over two decades. The national conservation strategy launched in 2024 says rural hedgehogs have declined by 30 to 75% since 2000, while towns may be starting to recover. They're listed as Vulnerable on Britain's Red List of mammals.

Gardens are where most of us can help, and most of it is doing less: leave the leaves, and check the bonfire before it's lit.