Why are some animals black and white?

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1:33What are these things? Are they alpacas? It's mentioned there. Hi, emu. Oh, is emu black and white? No. Welcome to CrowdScience from the BBC World Service, the show that answers your science questions. Oh, wow. Is that a capybara? Yeah, that's a capybara. Definitely not black and white. I'm Caroline Steele and I'm wandering around a zoo in Belgium with my very own guide, Johan Vreis. It's a secretary bird. Wow, they're really... They have more grey tones, so I wouldn't call it black and white. But we can't just stop and admire anything we fancy. Lions, not black. Lions, but we're in a rush and they're not black and white.

2:16Bye lions. Johan is helping me find some very peculiar animals. Debra's! You see them walking. Three zebras. Yes. They are most definitely black and white. And it's all thanks to a question from one of our long-time listeners.

2:35Yes, I am Jude Kirkham, and I'm calling from Williams Lake in British Columbia, Canada. So what's your question for crowd science? Why are some animals black and white? I was thinking about how a few years back there was a paper saying that zebras have black and white stripes to help and deter mosquitoes. And then I thought to myself, well, wait, pandas, also black and white. But not much else out there. You think pretty much everything is plagued by mosquitoes and parasites and flies and such. But it's quite rare in nature for animals to be black and white like that. There are maybe one or two other critters that elude my mind at the moment.

3:24But for the most part, black and white. Sort of atypical. I wonder why. Yeah, thank you so much. Oh, you're very welcome. Well, you're the ones who are looking into my questions. So I'll look forward to hearing what's going on with that.

3:43The animal kingdom is packed full of colour. Shiny blue peacocks, bright green frogs and deep red fish. But some creatures stand out because of their lack of colour. Is there something special about black and white animals? Why have some species evolved to be this way? And do they all have something in common? Now, just like Jude, when I think of black and white animals, one species immediately springs to mind. Oh, hi! Zebras. This one's like, what are you doing here? We're at Paradizer Zoo in Belgium, where Johan and I are joining three zebras for breakfast. I'm trying to see which pattern I like the best.

4:26It feels like almost hand-painted, but it's not because it's too perfect, the lines in a white. Yeah, it feels like someone has taken a horse, sprayed it white, and then painted it very carefully by hand and then dyed its mane. I mean, the fact that the hair on the back of their neck is also black and white striped and it continues from the stripes in their body, so a black stripe goes all the way up into their hair and continues through their hair. It has a very distinctive look. They stand out compared to the other animals. Yeah, they really stand out, don't they? It's like the opposite of camouflage, it feels like.

5:00It makes them stand out more rather than less. I feel like this is the most dedication to a colour patterning that we see in the animal kingdom. Like, they're not being like, oh, we'll have a few stripes. It's like, we are going to be entirely stripey. They definitely commit to a look. Yeah, they've committed to the look. Why do they look like this?

5:24They're fascinating animals. I got really interested in them because there just doesn't seem to be a very logical, obvious reason and why they're so obviously stripy. I mean, they're so conspicuous. You can see them from a long way away. They're obviously not trying to hide in a stripy background, as far as I can tell. And so the function of those stripes has always fascinated me. This is Martin Howe, Associate Professor at the University of Bristol. He specialises in animal vision. There have been lots of theories about why zebras have black and white stripes, and listener Jude mentioned one study in particular to do with insects.

6:00Well, Martin is the scientist that did that experiment. Many of us will have been bitten by horseflies. They are really horrible flies, even when they're not carrying disease. But if they're carrying disease and you get bitten by one on the plains of Africa, it can be a matter of life and death. So these horseflies, they also use vision to find zebras and to land on them. Already the theory was out there that maybe zebra stripes might be that way to try and avoid biting flies. I guess what we could do is we could try some semi-realistic experiments. These semi-realistic experiments involved Martin and his colleagues visiting some stables to test this theory with horses.

6:42Can you see that on your screen? Yes, we've got a normal looking horse, a sort of brown horse, and it's covered in a grey blanket. So I'm going to press play and this is a slowed down video. you'll be able to see coming from the left there's a blue line coming in with a dot on it and this is the trajectory that the fly has come in. In the video Martin is showing me I can see the horsefly fly in from the left. It comes in quite fast and then it slows right down. Flies in a few loops. And then it lands nicely on the rug. It looks like a slow motion horsefly doing its thing. If I now switch over to the equivalent, but zebra.

7:26I love how you say, I'm going to share the zebra. It is a horse dressed like a zebra. You can see it's a horse wearing exactly the same rug, but this time it's got vertical stripes. So it's not exactly like a zebra, but the width of the stripes is chosen to match the average width of a zebra stripe. So we're trying to get as close to a zebra as we can. So the horsefly flies in. A red line that approaches from the right. Just like in the other video. And you can see it comes in, it starts slowing down. But then... And then it turns and it accelerates off to the side. It just flies along the horse's body.

8:00So it just goes straight past. Completely missing the horse. You can almost see it's decision-making, where it comes in and it goes, hang on, that's not what I want, and it carries on. Do we know what it is about the stripes that's putting them off? Is it somehow like visually confusing? We originally set out to test whether maybe there were these optical illusions at play. So we did a whole bunch of tests where we tried different patterns of rugs. But it turned out that practically every high contrast pattern, every black and white pattern we used, as long as the pattern was sort of in the same scale of zebra stripes, so about sort of three centimetres or so kind of blocks of black and white, almost every pattern was really effective at stopping flies.

8:44so I don't think it's a stripe illusion that's that's making this happen instead what I think is happening is that flies have got terrible resolution compared to us so it's like looking through a pixelated television or you know really low resolution and so the flies actually when they're coming in from a distance all they're seeing is a gray blob and when they get to about two meters away the resolution of the eyes starts to pick up the white and the black patterns and And so it switches from being a grey object to being something with pattern in it. And so I think that's throwing the flies off.

9:20So it's not necessarily that they're sort of like, oh, I don't know how to land on this. It might be more that they're like, oh, this doesn't look like food. On we go. Waste of time. Exactly. Yeah. So interesting. So would it be worth, if I really want to avoid getting bitten by flies, maybe mosquitoes, Would it be worth, rather than using repellent, instead buying black and white paint and covering myself in stripes? Sadly, I'm going to have to rule out mosquitoes from this equation because mosquitoes tend to use smell more than vision for finding hosts. We're stuck with smell repellents for mosquitoes.

10:02But for horseflies, they really rely on vision. And so if you're worried about being bitten by horseflies, perhaps you're a horse rider or maybe a mountain biker or hiker who is in an area where there are horseflies, then wearing patterned clothing that's high contrast, black and white patterns, is going to reduce your chances of being bitten. So, listener Jude, you were close. The leading theory suggests zebras have black and white stripes to avoid pesky insects. But not mosquitoes, horseflies. Stripes don't look like good horsefly food close up.

10:43Line back at the zoo with Johan, because there's another black and white animal that listener Jude is curious about. Look, it's a panda! Giant pandas. could they be black and white to deter insects too? I think this is the first time I've seen a panda and it's really sticking its tongue out at us. That's because the caretaker, Robin, is just next to us. Hi! Nice to meet you. Nice to meet you too. Standing behind me is the giant panda's caretaker, Robin. And what food have you got? You've got carrots and... This is a carrot and a panda cake. Oh, nice! And the panda cake is the corn, the rice, the soy and the eggs, oil, is rich in the protein.

11:29Sounds tasty.

11:33When and why do pandas make that noise? They're kind of like... This is for Colmi. He hears me and he weighs more food. He's like, excuse me, I'm still hungry. I'm here, don't forget me. But I've got no time to get distracted by the surprising sounds coming from this panda. I'm here on a mission. He's got a completely white face apart from a black nose, black eye patches and very distinctively black ears. Black arms. Yes. Black legs. Yes. And a white belly. And a white belly and a white back. What an amazing animal.

12:20Well, there haven't actually been many theories about giant panda colouration. And I think that the mistake that we've been making as humans is that we so often see giant pandas close up in zoos or else in the movies. This is Professor Tim Carrow. He's the expert in animal colouration. His university profile picture is literally him wearing a zebra onesie. And he's also at the University of Bristol. Clearly the best place to study colourful or not so colourful animals. And of course, Tim has studied giant pandas. The giveaway for me was that we made contact with Chinese colleagues who studied giant pandas in the wild.

13:07and I asked them to send me 15 photos of giant pandas taken either fairly close up or at a distance. And in two of those photos, I thought that they had sent me the wrong batch of photos because I was unable to see anything in the picture other than rocks and snow. And then later on, I realized that, in fact, there was a giant panda in the center of that picture some distance away. and I kind of immediately that that clicked in my mind. You were sent photos of giant pandas in their natural habitat and you couldn't spot all of them that's how well camouflaged they were. That's correct yeah. Yeah it's hard to picture it being camouflaged because if you look at a photo of a panda or I guess for me seeing a panda against a green backdrop in the zoo it makes it stand out relative to the grass behind it or that kind of thing.

14:04But I guess we're not seeing pandas often in their natural environment. Yeah, that's absolutely right. In the forests of Western China, you've got black and white patches of snow and rocks and tree trunks at certain times of year. And if a slow-moving animal like a giant panda is seen at, say, 50 metres or 100 metres away, it's very difficult to distinguish that as being an animal from the snowy, rocky background in which it's seen. And so, in fact, this very startling colouration is actually a form of camouflage at a distance. So pandas are black and white for camouflage, which is hard to imagine if, like me, you've only seen them in zoos.

14:57But in China's snowy mountain forests, it can be the perfect disguise. But what about other black and white animals? Have they developed their distinct patterns for camouflage, like pandas, or maybe to confuse insects like zebras? We're looking at more black and white animals next. This is summer at its peak. Whole Foods Market Summer Fruit Fest is your invitation to eat the season. Fresh, organic, and bursting with flavor. Start your day with peaches and organic blueberries and yogurt. Build a grazing board with fresh fruit, prosciutto, and artisanal cheese. Then fire up the grill with no antibiotics ever proteins and fresh produce.

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16:18You're listening to CrowdScience from the BBC World Service, the show that sees your questions written in black and white and tries to come up with the answers. I'm Caroline Steele, and in this episode, we're answering a question from listener Jude in Canada, who wants to know why some animals are black and white. To try and find the answer to Jude's question, I'm getting a tour of Paridizer Zoo from Johan. So far, we've seen zebras and pandas. up next a small cat-sized animal. Skunky skunk skunk. Skunk skunk. The skunk. Oh look there's three over there. A very beautiful more white tail I see.

17:02And then like two big white lines that come from the head. And they also have a white line down their face sort of forehead to nose. But the width of their stripes is very different. So see this skunk slightly closer to us has really wide white stripes, whereas the other one has really narrow stripes down its back, so they look quite different from each other. So maybe it's an identification thing. Oh, bye, the skunks are going inside.

17:35You've picked the species of mammal that we probably know an awful lot about, and those are the striped skunks which live in North America. Here's Tim again, our all-round expert for animal colouration. They're using that as an advertisement, a warning advertisement, to other animals like bobcats or coyotes or mountain lions to stay away from them because they're able to spray very directly anal secretions that are absolutely disgustingly smelly, even into the eyes of some of those predators and can blind them. And so they are saying to those predators, look, I'm black and white. You don't want to try and mount an attack on me because I'm too dangerous.

18:19And also, I guess they're unique and sort of distinctive looking. So if it's happened to you once, you're going to be like, oh, no, there's that animal with the white stripes on its back running away. Yeah, that's absolutely right. I mean, you've raised a good question, because across North America, there's huge variation in how wide those black and white stripes are. And in places where there are a lot of predators on skunks, you get really distinct black and white banding. But in places where there are rather fewer predators, and so it's not so dangerous to live the life of a skunk, you have every sort of black and white band there.

19:01Sometimes you have pure black skunks or pure white skunks because they're not under such strong predation pressure. Interesting, but that's sort of really strong evidence that that is the purpose of the stripes. Yes, I think that's correct. So we've got reason number three to be black and white. To warn other species, hey, don't eat me, I'm going to mess with you. Oh my gosh. But our tour of the zoo isn't over yet. Look, there's lemurs sat on the roof. The ring-tailed lemur. Look at them, there's so many of them. Oh my gosh, they're so cute, they're sat so upright. Yeah, their faces are definitely black and white and their tails too.

19:47Yeah, so they've got white faces with black eye patches and black sort of noses. And then they've got these long black and white fluffy striped tails. Oh, but when they walk along, they raise their tail. Yeah, look, as soon as they start walking, they put their tail up. And then their bodies are technically grey, but we're going to allow them? They're very cute, so I'll probably... Maybe we're bending the rules here. Ring-tailed lemurs aren't only black and white, but as Johan says, they are very cute. Plus, they might highlight another reason some animals are monochrome. We haven't done really systematic research on the tails of any mammal.

20:40Here's Tim Carrow again. Our suspicion is because they carry that tail vertically when they're moving off as a group, we would suspect that it's a marker to say, here I am, please follow me. Yes, they really do that. They sort of sit with their tails dangling down and relax with their tails sort of floppy and loose. But then when they go to walk off to another bit of the group, their tails go like ping vertically upwards. Yeah, I think it's sort of let's stick together and please follow me. There are other examples of that in mammals. we think that the white spots on the back of tiger ears may be similarly a mother informing their offspring that I'm here, I'm walking off, look at these two bright signals, please follow me.

21:34And so a minority of these signals in mammals are probably something to do with group cohesion or else family cohesion. So sort of a bit like if you go on a walking tour and the person leading the walking tour has a flag so you know to follow them. Yeah, that's a great analogy. I hadn't thought of that. So reason number four, social signalling. That doesn't have to be waving a flag. Animals also have black and white features to look more attractive or even threatening to their peers. We have one final animal to visit. I hear penguins. The penguin. OK, so we've gone into the penguin enclosure and we are literally surrounded by penguins.

22:24How many penguins are there in here? Over 50. Over 50, yes. Wow.

22:34What kind of penguin is this? This is a Gentoo penguin. Gentoo penguin. Okay, so it has an entirely white belly and an entirely black back. And then the back of its wings are black, but the underside of its wings are white. Its face is black, but its eyes are white. And it's getting very interested in our microphone. I feel like it's moments away from giving it a peck.

22:58So if we look behind us, we're surrounded by water full of swimming penguins. Sometimes it's hard to see them because it's like... Yeah. From above, you really see only black in a way. I mean, they really don't stand out against the rocky bottom, do they? They blend in quite well. And they also move so fast that it's hard to keep up with them.

23:27I sometimes like to think of it as being like their tuxedo. And that's what all penguins, modern penguins that are alive in the world today, all have that same pattern and colouration. This is Hannah Rowland, a senior lecturer in the Department of Evolution, Ecology and Behaviour at the University of Liverpool in the UK. We're lucky as scientists to have discovered fossil penguins from 36 million years ago. So a penguin called Inkayaku paracinensis is a fossil from Peru. And surprisingly, it's not black and white like modern day penguins. It was actually grey and a reddish-brown in its colouration.

24:12So penguins haven't always been black and white. That's like a recent thing. It is in evolutionary terms. So penguins evolved their black and white tuxedos about 14 million years ago. And that's when the climate on the planet started to cool and Antarctic ice sheets started to expand across the planet. and our penguins that we have on the planet today, they started all those years ago to push into these deeper and more harsher marine environments that we know they live in today. Now, you might think, because we know when penguins' colouration evolved, surely we have a clear idea of why they're black and white.

24:54But actually, there are lots of competing theories. Maybe it helps them survive harsh conditions. You've got wind, you've got snow, you've got moving in and out of water. So the black feathers that they have on their backs, these are loaded with this pigment called melanin. And melanin, it makes their feathers much more resistant to mechanical damage. Or it could act as camouflage from above and below. When the animals are seen from below, their light bellies blend in with the bright sky that they're being viewed against. Or when they're viewed from above against a dark background, particularly in the water like a penguin is, that they blend in with the dark background of the sea that they're living in.