Researchers reveal the secret life of hedgehogs

“I was surprised to find that hedgehogs don't retreat into the forest but instead opt to nest in gardens and near people's homes. However, when it's time to hibernate, they prefer nesting under large tree roots in the forest,” says Beate Strøm Johansen.

She is a zoologist Beate Strøm Johansen at the University of Agder.

In recent years, the hedgehog population has declined. In 2021, they were red-listed. Hedgehogs are a threatened species in Norway and several other European countries.

In a new study, Johansen and her research group have tracked the lives of urban hedgehogs in Kristiansand, southern Norway.

“We've tracked nine hedgehogs, but they aren't exactly a group. They don't live in herds. Hedgehogs, like most other mammals, live solitary lives and have their own home base where they spend the night,” she says. 

A solitary wanderer

“Very few mammals are herd animals. We think they live in herds because lions and wolves get so much attention on TV,” says the zoologist.

She points to the mustelid species, which contains weasels and badgers. These are also solitary animals. 

“Mammals usually wander around alone. Solitary animals only meet when they mate and when raising their young. For female hedgehogs, this means four to six intense weeks with her offspring,” says Johansen.

Fieldwork in urban areas

The new study involved fieldwork conducted both day and night. The night work was carried out by bachelor students at the University of Agder. But during the day, the students also tracked hedgehogs that were resting and sleeping. 

From August to November – just before hibernation – they monitored the lives of nine hedgehogs near the university in Kristiansand. The university is located in a residential area close to the forest and the popular recreational area Jegersberg.

Radio transmitters were attached to the hedgehogs. Six of them retained the transmitters long enough to be included in the study.

Wake up in the evening

Hedgehogs are nocturnal. In the evening, they come to life. Around 11 PM, they're on their way, ready to find food.

Hedgehogs are not picky eaters by human standards. They devour earthworms and centipedes. This is typical fare for them. Beetles, slugs, and larvae? Crunch, chew munch – those too.

Eggs and berries? Delicious. Dead birds, mammals, amphibians, and reptiles? Yum. 

You might think they can tolerate anything. But they can't. The zoologist warns:

“They will drink milk if they come across it, but it causes green, slimy diarrhoea and makes them very sick.”

Do not give them milk

“Don't put out milk for hedgehogs. Instead, leave a bowl of water,” says the researcher.

She reminds us that hedgehogs, badgers, squirrels, birds, and all other animals appreciate having access to water in a bowl. Summers can be dry and sunny. Two to three months can go by without rain.

“This is when food becomes scarce for many animals. Earthworms and slugs retreat underground and encase themselves. They don't emerge at all. It can help these animals to put out water and perhaps leave out dry cat or dog food. Badgers and hedgehogs both enjoy this,” says Johansen. 

They head home in the early morning

Most hedgehogs have had enough by around three in the morning. Some, however, stay out until five or six in the morning. Then they return home to sleep.

The hedgehogs from this new study were usually home and in bed by 5 AM.

Sometimes, their nightly adventures are about more than just food. Occasionally, hedgehogs are out looking for a mate, if it's that time of year.

“They mate in the spring and can have up to eleven young, but four to five is more common,” she says. 

Exhausted hedgehog mother

If you come across a hedgehog during the day, it is most likely an utterly exhausted mother searching for food. She is starving because she is nursing her young.

After about four weeks, the young start following their mother outside the nest in search of food. Things move quickly now. In another one to two weeks, the young feel ready to fend for themselves. They then set off on their own.

They leave their mother and find their own place to live. One might find a spot under the terrace of a neighbouring house. Another finds the woodpile by a different neighbour's garage. There, they build their own nests.

They have multiple places to live

Hedgehogs have three types of homes or nests.

They have simple summer nests where they live alone. They use more solid breeding nests where the mother stays with her offspring. And in winter, they have sturdy hibernation nests, where they sleep through the winter all alone.

In their nests, they can rest and sleep. They can hide and recover. Until nightfall.

They often have several nests at the same time. Usually, they have about ten nests. They likely choose one over another simply because it's close by.

When it's time to sleep, it's convenient to have a hideout here and there. They may also need to seek shelter quickly, explains the zoologist. 

28 nests for six hedgehogs

The six hedgehogs from the area around the university had 28 nests in total.

16 of these were under or inside a building, such as a garage, veranda, or terrace.

12 nests were in gardens and other areas with hedges, bushes, and forests. Most nests were made of grass and leaves.

“People's gardens often have a variety of vegetation such as lawns, flowers, hedges, and some grass and stone under terraces. It's a habitat suitable for hedgehogs. Here, they can search for food and hide in their nests if threatened,” says Johansen.

Males occupied 18 of the 28 nests. Females inhabited 10. Each hedgehog switched nests between zero and 14 times while the students monitored them. Three females changed nests 15 times. Four males changed nests 21 times. In total, the six hedgehogs changed nests 36 times.

But none of them used another hedgehog's nest.

Full of parasites

Hedgehogs generally do not share nests. They are full of parasites and all kinds of critters. Researchers believe this is why they do not share nests.

“These hedgehogs are walking ecosystems. They would likely prefer to be parasite-free. Hedgehogs can also carry ringworm, a fungus that can infect humans if handled without gloves. They may cough and sneeze a lot, which means they probably have lungworms,” says Johansen.

Hedgehogs are also food

There are animals that might consider eating a hedgehog, which is unfortunate for the hedgehog. Equally unfortunate is that hedgehogs are not very fast on their feet. Even when they try to move quickly, they are still slow. 

When threatened by a fox or cat, they roll into a ball, extending their spines outwards. But sometimes, that is not enough, as seen in these real-life scenarios, according to the researcher:

A badger strolls across the lawn. The hedgehog should have run for its life but stays still. It curls up into a ball and extends its spines. 

The badger could not care less. It has its own trick and rolls the spiky ball around. The badger grabs onto the soft spot on the belly and pulls the hedgehog out. And that's the end of the story. 

The fox is more patient. It lies a little distance away and waits. It waits until the hedgehog feels safe. Then, the little animal's nose peeks out from between the spines. Eyes look forward. That is when the fox strikes. And just like that, the hedgehog is gone. 

Hedgehogs hibernate

“People used to believe that bears hibernate through the winter. But they don't. Only small animals like hedgehogs and bats truly hibernate,” the researcher says.

Bears and badgers tend to sleep during winter, but it's a light sleep and not true hibernation. Their bodies are a bit too large to lower their body temperature enough to enter hibernation, the zoologist explains.

“Hedgehogs, on the other hand, do go into hibernation, and it's best for them if they can lie beneath the snow. The issue is frost without snow,” she says.

Hedgehogs sleep through the entire winter but wake up approximately every 11 days, often just to confirm that the nest is intact and that spring has not yet arrived.

“One theory suggests they need to wake up to enter deep REM sleep when entering a new hibernation period,” says Johansen.

Prefer large trees and robust winter nests

Around September, hedgehogs seem to start getting ready for winter.

They prepare to hibernate. At this time, they need a more permanent nest. It has to be strong enough to withstand winter.

An important finding in the study is that hedgehogs prefer to live under large trees, near the roots of pine or deciduous trees.

“They wanted a thicket around their sleeping place under the tree roots. Then they could bring in moss, leaf blades, and long grass stems to build a nest and seal off the entrance. This prevents wild animals from pulling them out. They also want the nest to be a bit tight to guard against the cold,” says Johansen.

Reference:

Korslund et al. Home Range, Movement, and Nest Use of Hedgehogs (Erinaceus europaeus) in an Urban Environment Prior to Hibernation, Animals, 2024. DOI: 10.3390/ani14010130

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Read the Norwegian version of this article on forskning.no

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