"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."

That's according to zoologist Beate Strøm Johansen at the University of Agder (UiA).

In recent years, the hedgehog population has declined. In 2021, they were redlisted. 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.

"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."

Lonely 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 out that mustelids are lonely creatures, or solitary as scientists say.

"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," Johansen says.

Fieldwork in urban areas

The new study involved fieldwork both day and night. Bachelor's students at UiA handled the night work. 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 of Agder in Kristiansand. The university is situated in a residential area close to the forest and the popular Jegersberg recreational area.

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 eleven, they're on their way. That's when they go out to find food.

From our perspective, hedgehogs are not fussy about their menu. Earthworms and centipedes are devoured. This is typical fare for them.

Beetles, slugs and larvae are gnaw-gnaw-gnaw, as well.

Eggs and berries, yum-yum. 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."

Don't 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 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."

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 Kristiansand and this new study were usually home and in bed by five.

Sometimes, night life is about more than food. Sometimes 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 are more common," Johansen says.

If you come across a hedgehog during the day, it's likely a very exhausted mother searching for food. She's starving because she's nursing her young.

After about four weeks, the young start following their mother outside the nest in search of food. Now it progresses quickly. Another one to two weeks, and the young feel ready to fend for themselves. They then embark out on their own.

They leave the mother and find their own places. 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.

Hedgehogs have three types of homes or nests.

They have simple summer nests where they live alone. They use more solid brood nests where the mother stays with her offspring. And in winter, they have durable 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 about ten. They likely choose one over another simply because it's close by.

When they're sleepy, it's convenient to have a hideout here and there. They might also need to find shelter quickly, explains the zoologist.

28 nests for six hedgehogs

The six hedgehogs from the area around the university in Kristiansand had 28 nests in total. 16 of the nests 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 forest. 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 is 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 0 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 as many as 36 times. But none of them used another hedgehog's nest.

They are full of parasites

They generally don't share nests. Hedgehogs are full of parasites and all kinds of critters. Researchers believe this is why they don't 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 those who might consider eating a hedgehog. That's unfortunate for the hedgehog. Equally unfortunate is that the hedgehog isn't very fast on its feet. It's slow even when it tries to speed up. When threatened by a fox or cat, they roll into a ball, extending their spines outward. Then what happens could be like these stories, based on actual events, according to the researcher:

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

The badger couldn't care less. He has his own trick and spins the spine-ball around. The badger grabs onto the gap on the belly side and pulls the hedgehog out. And that's the end of the story.

The fox is more patient. He lies down a bit away from the hedgehog and waits. He waits until the hedgehog feels safe. Then the little animal's nose peeks out from between the spines. Eyes look forward. Then the fox strikes. And the hedgehog is no more.

"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, not real 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 eleven days, often just to confirm that the nest is intact and that spring hasn't arrived yet.

"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. Then they need a more permanent nest. They need a nest that can withstand the winter.

An important finding of 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.

Lars Mørch Korslund, Beate Strøm Johansen et al.: 'Home range, movement, and nest use of hedgehogs (Erinaceus europaeus) in an urban environment prior to hibernation'. Animals, 2024. Doi.org/10.3390/ani14010130