Instant Genius - Why hedgehog numbers are falling and how we can stop it

Episode Date: January 29, 2024

Whether it’s from reading Beatrix Potter’s Mrs Tiggy-Winkle or from encounters in our own gardens, many of us have a special place in our hearts for hedgehogs. But sadly, the charismatic mammals are having a bit of a hard time of late, with their numbers declining across the globe. So, what can we do to help them? In this episode we catch up with Dr Sophie Lund Rasmussen, a research associate at WildCRU, at the University of Oxford, or as she is otherwise known Dr Hedgehog. She tells us about the current state of hedgehog conservation, what she’s learnt from many years of studying them and how we can make our gardens more hedgehog friendly. To find more about her work studying hedgehogs, follow her on Facebook. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Each week you'll hear world-leading scientists and experts talking about the most fascinating ideas and science and technology today. I'm Jason Goodyear, commissioning editor of BBC Science Focus. Whether it's from reading Beatrix Potter's Mrs Tilly Winkle or from encounters in our own gardens, many of us have a special place in our heart for hedgehogs. But sadly, the charismatic mammals are having a bit of a hard time if late, with their numbers declining across the globe. So what can we do to help them? In this episode, we catch up with Dr. Sophie Lund Rasmussen, a research associate at Wildcru at the University of Oxford, or as she has otherwise known,

Dr. Hedgehog. She tells us about the current state of Hedgehog conservation, what she's learned for many years of studying them, and how we can make our gardens more Hedgehog-friendly. You're a research that studies hedgehogs, and you're also known as Dr. Hedgehog. So how long have you been doing this? And why did you decide to study hedgehogs in the first place? Well, I started studying hedgehogs around 2011. I was a biology student and I was also a volunteer at a wildlife rehabilitation center in Denmark where we took care of sick and injured and orphaned wildlife. And I've always loved hedgehogs. And then I was assigned the task of bottle feeding orphaned hoglets or hedgehog juveniles. And it was just such a wonderful experience. And I started

asking the questions. So what actually happens when we handraise the hedgehogs? Does it really pay to do that? Because it's a lot of work. It was battlefielding every three hours. And would they actually be able to survive out in the wild, not having been with their mothers and not having been taught how to survive out there? And then I was about to write my master's thesis in the wild. And biology and I decided I would try and use hedgehogs as a focus for that thesis. And then I discovered that when reading the literature, the scientific literature about hedgehogs, not many studies had been conducted. I was surprised about that because it's a hugely popular species and I just assumed that it would have been studied a lot. So that's when I decided I was going to focus on hedgehogs and really

make a difference and contribute to science with that. So let's start with the basics then. We're a science brand. So scientifically speaking, when we're talking about the species hedgehog, what are we talking about? What family do they belong to? Things like that. So we do have a total of 19 different species of hedgehogs all over the world.

And it was actually quite interesting because very recently, a new species was discovered in China. So up until a few weeks ago, we only had 18. species. So in the UK, we do have the European hedgehog. That's Elinaceous, Europeans in Latin. And it's a spiny, nocturnal mammal. So it has these spines on, and it's about between 5,000 and 8,000 spines on a hedgehog, depending on the size of the hedgehog. And this is, of course, a feature that protects them against the different species who would want to eat them, such as larger birds of prey or foxes or badges, for example,

here in the UK. So this is their strategy to have the spines to protect themselves. So it's a very characteristic mammal. Everybody could recognize a hedgehog, which is actually a great advantage when you study hedgehog, because then people know what they're dealing with. So if you use citizen science, asking people to get involved in the research, you're pretty sure that they are dealing with the right species. When they said they saw a hedgehog, they actually saw a hedgehog. So let's have a look at their behavior then. What does a typical day look like for a hedgehog? Yeah, so the hedgehog is a nocturnal species. So usually they'll wake up around sunset and become active and they'll leave their day nests and start foraging. And the hedgehogs, they forage

forage forage for forfeit prey. They like snails, slugs, worms, insects, but they also eat carrion, for example. So they browse around people's gardens. This is a typical habitat where you will find them today. And they search for food. And during spring, they of course also search for maids. It's the mating season, and then they mate, and then the juveniles are born in the summertime, and the males are actually not part of that. They only mate, and then they take care of themselves.

So all the raising of juveniles is up to the females. And when the juveniles have left their mothers after around six weeks, seven weeks of care with their mother, then the mother is ready to start preparing for hibernation. So she has to gain a lot of weight because it's really hard for her to nurse all the juveniles and she loses a lot of weight. But then she has to forage and prepare for hibernation because as the hedgehogs feed primarily on invertebrates, the wintertime is not a very good time for them because there's no food left. So the hedgehogs have the strategy of going into hibernation to basically save the energy resources throughout the winter when there's no food available.

So it's like when you set your computer phone to power saving mode. So it's still alive. It's still functioning, but it saves all the energy and only focuses on the vital functions. So for the hedgehogs, it means that, you know, the heart rate goes down. The whole metabolism is just reduced in activity so that they basically save a lot of energy throughout the winter. And when the weather gets warmer again and the food items, the insects start appearing again, they'll become active again. And this, of course, depends on the temperature. So normally you would say that they hibernate until around March-ish in the UK, but it completely depends on the temperature. And we've also seen in recent years that sometimes March is very mild and very nice and then suddenly it starts snowing. And then the hedgehogs may go back into hibernation. My research is a shown that, I mean, we know that the hedgehogs are not sleeping throughout the whole hibernation period. They tend to wake up every 10 days to kickstart the system, but then sometimes they

decide to change nests. Sometimes they wake up because they're sick or perhaps too poorly or too emaciated to survive, so they have to go and search for food. So sometimes you can actually see an active hedgehog during the hibernation period. And sometimes it's because they're in need of help. Sometimes it's just because they had to change nest because the nest was disturbed or it turned out that the nest was not good enough, perhaps not insulated enough. So you can actually encounter a hedgehog during winter time also. So you mentioned there that the males don't help raise the young. So are they typically solitary animals? Yes, they are solitary animals. So they're only actually together when they form a part of a sibling group that's being raised by the mothers. Sometimes

the siblings can actually, when they leave the mother's nest, stay together for a few weeks. Sometimes they prefer to follow each other and stick together during their first, you know, weeks out on their own because it's a dangerous world out there, right? Sometimes we also witness hedgehogs sleeping in the same nests together. It does occur, but officially they are solitary. They're not territorial. So there can be many hedgehogs, you know, roaming around in the garden. There may be aggressive in cancers, especially if you put artificial food out for them,

supplementary feeding. So they may actually fight over the food if there's only one food bowl with cat food and water. And also during the mating season, of course, the males will fight each other over the very nice females. So in the wild, how long do they live? What's their sort of ballpark lifespan? Well, I've actually researched this. So you can count the age of a hedgehog by counting the growth ring. in their jaw bones, just like you would do on trees, you know, earrings and trees.

And that's because the hedgehogs are hibernating. So during the hibernation, they don't grow because they don't get, you know, nutrition. And this actually causes small lines forming in the jawbone. So one hibernation would equal one line in the jawbone. So what I did was through my research project, the Danish hedgehog project, where people collected dead hedgehogs for my research. We had 400 hedgehogs that still had an intact jawbone, which we could use for these studies. So we basically cut out microscopic pieces of the jawbone and dyed them with a purple dye, and put them under the microscope.

And then we can count the growth rings in the jawbones. And we found the world's oldest hedgehog. His name was Torval. He reached the age of 16 years. Wow. And he died in care sadly because he was attacked. by a dog and got infected. And he wasn't found in time for the antibiotics to kick in.

But 16 years of age, it was completely mind-blowing. And I was really touched by it. I remember sitting, looking into the microscope, I was counting like the 17th sample of the day and counting and counting. And then suddenly I just saw all these lines and I thought, whoa, I need more coffee. I'm seeing double here. And I had to step back from the microscope and look in again. And then suddenly I realized, well, that was 16 lines because previous studies had only revealed a maximum age of nine years.

So that was amazing. Of course, we had a sample size of around 400 hedgehogs. The average age was sadly below two years. So, I mean, they don't normally get to become that old, but it was just really great to see that it could actually happen. So is that shorter lifespan due to predation and things like that? Yes, I mean, the hedgehog. live hard lives. They have many threats. Of course, traffic is a major influence, road kill collisions. And depending on who you ask, it's estimated that up to one third of the

population is killed on roads every year. So that's a huge impact. But of course, there are also other threats to the hedgehogs and all the threats are mainly anthropogenic. So they are caused by humans. The habitat quality in the rural area is really decreasing due to to intensified agricultural practices. So first of all, a lot of pesticides are used. So all the insects they would normally feed on slugs and insects are more or less eradicated in the cultivated areas. In the old days, the fields tended to be smaller,

and they had these hedgerows in between them. And this was where the hedgehogs lived. Today, the fields are large and the hedgerows have been removed. So now suddenly the hedgehogs don't really have any places to stay in these areas. And then there's all the machinery, all the large machines that cultivate the areas that may also endure the hedgehogs. And this is a huge issue. So suddenly the amount of good habitats have decreased a lot. So these days you primarily see hedgehogs in residential areas in areas occupied by humans because this is where they can survive.

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So how do they see the world? What senses do they use? So we know they have pretty poor eye vision. So it's the sense of smell and it's the hearing they primarily use. I'm actually going to investigate hedgehog hearing for the first time very soon because we have no idea which frequencies they actually hear. And I'm really interested in whether they communicate. through ultrasound because they do not tend to vocalize a lot. The juveniles can issue sort of a whistle sound when they're calling for their mother. And during aggressive encounters between the adults, there are some different screams they can make, but they don't appear very chatty.

So when they encounter each other, they seem to be communicating, but we can't hear anything. So I'm really curious as to whether they actually use ultrasound. So this is on my to-do list for research coming up. So sort of anecdotally speaking for myself, I grew up in the countryside, but for a long time I've lived in cities. When I was younger, I used to see hedgehogs all the time. And to be honest with you, I can't remember the last time I saw one now. So what is their current conservation status? It's so sad. It's so devastating. The hedgehogs are declining massively. And depending on the methods used to estimate the decline, we're looking at all.

and up to 75% decline. I mean, it's three out of four hedgehogs that have disappeared in the rural areas. It's a serious problem. In the UK, their status on the so-called IUCN Red List is vulnerable. But in the European list, it's actually least concerned. And that's because we've not had the proper data to document this decline. But we do have that now. And I was asked as one of two assessors to reassess their status recently. And it is going to change, but it will be published later this year. So what's causing the decline then? So it's road traffic accidents, lack of suitable habitats,

a lot of human caused trouble. So for example, the hedgehogs tend to live in people's gardens now. We share habitats with the hedgehogs. And they are prone to a lot of injuries in the garden. For example, we see, sadly, a lot of hedgehogs that are attacked by, dogs in the gardens. Hed sharks can fall into puns and swimming pools and drown. They're really excellent swimmers, but if the edges is too steep, they can't get up again and they'll drown. Then there's the use of pesticides, both of course in the agricultural areas, but also in people's gardens.

Because they can actually eat, for example, rat poison and mouse poison if it's just, you know, freely available, if they can access that they'll eat it. But they also eat carrion. So if they found like a rat or a mouse that had been poisoned, they would eat it and then get secondary poisoning. The same goes for the poison you put out for slugs and snails, for example. They can eat the snails and slugs that have been poisoned, but they could also eat the poison directly. So it is an issue. There will soon be research published on this subject, and we do see a high occurrence of pesticides in the hedgehogs we've researched. So when it comes to risks in the garden and sharing habitats with humans, they are also at risk of being injured by

garden tools such as streamers, for example, or some models of robotic lawnmowers. So there are a lot of different threats to the hedgehogs. Also, the lack of suitable nest sites. So people tend these days to have like really simple neat gardens with short grass, no mess and wooden terraces. And that's about it. And there would be no place for a hedgehog to live. because you don't have the bushes, the shrubbery, the piles of garden waste. So the hedgehogs have no place to live. So this is also a problem. And then when people build bonfires, if you have a completely boring garden in terms of biodiversity and everything,

and you suddenly make a bonfire and you put out all these lovely garden waste pieces, you know, all these leaves and branches, then suddenly the hedgehogs go, wow, they build us a home. and they'll move into this pile of leaves, and then suddenly it's slided and the hedgehogs are burned. So this is a huge issue as well. So having said that, is there anything anybody listening can do to make their gardens more hedgehog friendly? Yes, so first of all, there's a tendency, especially in the UK, I think, to have massive fences around your garden. So this doesn't allow the hedgehogs to move around freely in search for food and mates. So it's really important to make sure that the hedgehogs,

can easily access your garden. So if you don't already have a hole for a hedgehog, then please consider making a hedgehog highway. So basically cutting a hole into your fence, allowing the hedgehogs to move around freely in the search for mates and food, and then provide shelter for the hedgehogs. So you could purchase a hedgehog house.

You could make sure they can access, if you have a wooden terrace, for example. If they can live underneath the wooden terrace, they're happy to do so. You could also make sure to plant a lot of different, bushes and create natural habitats for the hedgehogs or just let areas of your garden grow wild to attract a lot of biodiversity because we've all heard how the insects are disappearing and the hedgehogs feed on insects. So how are they supposed to survive that they can't forage probably? So if I am lucky enough to have the hedgehog in my garden, what should I feed it?

The best way to feed a hedgehog is actually to have a wild garden attracting a lot of biodiversity because the insect, slugs, snails are their natural food items. But if you can't really provide that, the alternative would be to provide supplementary food in the shape of cat food and then put water out for the hedgehogs as well. You just have to keep in mind that the hedgehogs may share food bowls because they're not territorial. And they may share food balls with your dog or your cat in the garden.

So please make sure to keep a strict hygiene. Please make sure to wash the food bowl so that they don't infect each other. And it's also a good idea if you have many individuals, many hedge sharks coming into your garden to feed to have several different feeding stations just to reduce the risk of aggressive encounters between them. So I've heard that you shouldn't put milk out for them, is that right? So when they've been weaned from their mother's milk, it's not natural for them to drink milk. And it appears they are lactose intolerant so that they suddenly start producing the enzymes

needed to digest the milk sugar. So this may cause diarrhea in the hedgehogs. So just to avoid that, we just provide cat food and water instead of milk just to be on the safe side. So you mentioned earlier the project that you ran the Danish hedgehog project. And you mentioned that fascinating finding that you found a 16-year-old hedgehog. But what other things did you find? So I basically decided to use the dead hedgehogs to understand the living. So my research is very multifaceted, you could say, because I study all sorts of things relating to the hedgehogs, because I basically want to understand why the hedgehogs are declining,

which causes this decline and what can we do to stop it. So we've also used all these 697 dead hedgehogs collected from all over Denmark to study their end of parasites, for example. sample, their dental health, which bacteria they carry. And this is, of course, with the focus on which pathogens they might carry, what makes them sick, how can we efficiently treat that if they're admitted into care? So we've studied all sorts of things about these hedgehogs, and we get so much exciting knowledge out of this. I also want to use fecal samples from these dead hedgehogs to understand exactly what the hedgehogs eat nowadays. Because 30, 40, 50 years ago, studies were

conducted on the diets of hedgehogs. And these studies were based on a macroscopic examination of the food inside the hedgehog's stomachs, so the food contents of the hedgehog's stomachs. But imagine how to actually determine the species of beetle, hardly digested, you know, found in the stomach of a hedgehog is like you pull out a small leg and go, oh, that's probably a whatever. It's really hard to determine. So I want to use what is known as e-DNA. So basically test the fecal samples for DNA to see exactly what the hedgehogs have eaten because that wouldn't require any legs to be present. So partly digested food items, it's really difficult. So by using the E-D-Na method, we can describe exactly which species the hedgehogs have been eating. So this is also a

a next step for my research. We've also looked at pesticides and hedgehogs to which poisons accumulate in the hedgehogs. And that is really interesting, especially because we share habitats. So when the hedgehogs are exposed to different pesticides, we are also likely exposed to the same ones. So sort of by way of closing then, are you optimistic about the future of hedgehogs? I think education is a way forward. If we can actually inspire people to do something to help the hedgehogs in their everyday lives, we can make a difference for the hedgehogs. Their future lies in the gardens. We share habitats. So if people would make their gardens hedgehog friendly and provide supplementary food for the hedgehogs, make sure to attract a lot of biodiversity into their gardens,

allowing the hedgehogs to search for natural food items, try not to run over the hedgehogs on the roads, and just in general take care of wildlife. They do have a future. We can see. We can see. In the UK, people's trust for endangered species and the British Hedgehog Preservation Society, they run a campaign called Hedgehog Street. And it's been running for over 10 years now. And it appears that all their hard work, all their communication to the public, all their engagement and conservation campaigns have actually contributed to at least stabilizing the decline in the urban areas, it appears.

And that's really, really important. But if we all come together and really try to do our best to help save the hedgehogs, I think they do have a future. Thank you for listening to this episode of Instant Genius. Brought to you from the team behind BBC Science Focus. That was Dr. Sophie Lundrasmison, a research associate at Wildcru at the University of Oxford, or issues otherwise known, Dr. Hedgehog.

The current issue of Science Focus is out now. Pick up a copy wherever you buy your favourite magazines, or download us on your favourite app store. You can also find us online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision

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