Cold weather and a blanket of snow have left her short of food so she’s been forced to hunt in the day – and now she’s got competition. A kestrel. It’s one of the downsides of hunting during the daylight hours. And even worse, the snow means she can’t see her prey. So how do you find your food when it’s hiding out of sight? Hunger forces the kestrel to take a chance. But his razor-sharp eyesight isn’t enough in these conditions. Luckily for the barn owl, she has another superpower in her armoury. Flying blind won’t stop her eating. Because although she can’t see it, she can hear her prey, even under the snow.
The kestrel simply doesn’t have what it takes. So how does an owl’s extraordinary hearing work? [SOUND OF OWL HOOTING] Some owls have ear tufts but these feathers aren’t used for hearing. They’re more about communicating mood. In fact, the owl’s whole head is designed for listening. Its distinctive round face is shaped like a satellite dish, specifically to detect sound. A ring of stiff feathers channel the sound towards the true ears, which are hidden at the side of the face. Some species of owl have one ear opening higher than the other. This unique adaptation allows the owl to work out what height a sound is coming from, as well as the direction. Sound arriving at the left ear before it reaches the right tells the owl it’s coming from below. At certain frequencies, an owl’s hearing is ten times more sensitive than ours.
This extraordinary skill means this great grey owl can locate its prey even when it’s out of sight. Dogs watch us all the time in a way that no other animal does. He senses whenever we’re going to go out and he knows before we even make a move. They read our body language and that’s how they know we’re going to take them for a walk; before we think we’ve made the decision ourselves. It’s this constant observation that can sometimes appear to give them a sixth sense. Max is a red collie cross, normally full of energy and enthusiasm. But in 2008, his owner, Maureen Burns, noticed that something was wrong. I thought at the time Max was fading – he was nine and a half. And I was preparing myself for losing him because he just wasn’t happy. Wouldn’t come with me, wouldn’t sit by me, wouldn’t sit on my lap. And the odd signs: he would come up and touch my breast with his nose and back off, so desperately unhappy, with such a sad look in his eyes. Maureen had a small lump in her breast but her latest mammogram was clear, so she presumed all was okay. Initially I thought: “Oh, it’s just another lumpy breast, as people get.” But then, I sort of connected it with the dog, with his odd behaviour.
And one day, I was looking in the mirror in the bedroom here and I looked across in the mirror at Max’s eyes – he was on the bed as he is now – and I knew it was cancer. Maureen went to her local hospital, but both a scan and a mammogram came back negative. It took a surgical biopsy to finally detect the cancer. Maureen had it removed and the change in Max’s behaviour was instant. The day I was picked up from the hospital, he was his old, hyper self again. He put his nose across my breast to check where the operation had been and he was wagging his tail and his eyes were happy. It was unbelievable, the change in him – instant. I love Max so much and I owe him so much. And even before I go for a check-up now, I get him to check me out. And if he’s happy and wagging his tail, I’m happy and I know I’m okay. Seek! Seek! Seek! We now know that dogs like Max are smelling the tiny volatile chemicals given off by cancerous tumours. Most dogs can do this; they just don’t know that we’re interested. But with a little training, dogs can accurately pick out a cancerous patient from a selection of urine samples. Good girl! Good girl! They can even be taught to let diabetics, like Steven, know that his blood sugar levels are smelling low, long before he can feel it and definitely before he passes out. Dogs like Steven’s are now transforming lives all over the country. They’re being trained to detect the early warning signals for severe allergic reactions, epileptic fits and narcolepsy. He’s the perfect elephant. Andre Cox has worked with elephants for 25 years. And knows the obvious behaviours that will show the elephants are hearing the infrasound. Andre, even though these are rescued elephants, do you still see a change in behaviour when it thunderstorms approaching like they were in the wild. When they hear a thunderstorm, they will more than likely turn the backsides together face into the thunderstorm, ears out with a spontaneous freeze. That is a secret message or something that happens and they just stand still. After the spontaneous freeze you will the will more likely start chatting among each other, low rumbles. If they respond in that way to our thunderstorm, then that’s proof in a way that they can hear a part of the sound spectrum that we can’t even tell. Absolutely, absolutely without a question of doubt. Although the speaker is positioned close to the elephants, the infrasound it produces will have the intensity of a distant storm. The herd is busy feeding, so Patrick is looking for a definite change in behaviour.
Bruce I think we’re ready to play the speaker. OK Patrick, audio in 2 seconds. It may seem strange, but because the camper van is generating sounds below are hearing threshold, we can’t hear it. But we can certainly see it as air inside the van vibrates with sound energy. the elephants react immediately, turning to the speaker. They’re clearly reacting to the sound. But Patrick can’t hear a thing. That’s incredible, they’ve all stopped and they’ve changed their behaviour as soon as Bruce started playing that sound from the camper van. You can even hear them vocalising. Their ears, fanning out. It’s absolutely amazing how it completely changes their behaviour. Bruce it worked! There’s absolutely no question about it. And their ability to determine the direction the sound was coming from, I was really impressed with that. The elephants are back feeding now, but virtually the entire herd turned and faced infrasonic speaker, listening in to that secret sound of the storm. This hidden channel of infrasound could explain a great mystery of the natural world. How elephants know where to go when they migrate vast distances in search of water. So he’s sniffing around all the time, getting used to the environment. Never a dull moment, they’re always very active. Their metabolism is very high. No such thing really as a fat wolverine. [Laughs] And they don’t hibernate like a bear. So they just keep going all winter. That’s right. They don’t have much time. It’s all about survival, you know. And Mother Nature doesn’t give an animal like this a lot of margin for error. As scavengers, most of the Wolverines diet is dead animals. Creatures that have perished in these extreme conditions. And to find their food, wolverines take advantage of one of nature’s most destructive forces, avalanches. As snow thunders down the mountainside, mammals are often buried beneath. It’s thought wolverines can sniff out frozen carcasses even deep beneath the snow. To test this out, Helen buries some frozen meat deep in the snow. She’ll return in a few hours with Jasper to see if he can find it, just using his sense of smell. Before that, she’s got a demonstration to show how our noses and the Wolverines work. It involves an orange. When I sniff the orange, it’s really strong this one. The scent molecules from the orange are going up my nose and they’re going up to the top here. And there’s a structure up there that’s called the epithelial membrane, and that is where the odour detector’s are. It’s thought smell works like a lock and key.
The scent molecule is the key and will only fit certain locks. The odour detectors. We have four hundred different types of locks. But scent molecules can hit many combinations of these receptors So we can identify thousands of different smells. Most mammals detect scent in the same way, but for wolverines it’s all about sensitivity. Detecting the tiniest traces of scent even deep under the snow.
So let’s see how Jasper gets on finding the buried meat. They start several hundred meters away and let Jasper choose the course. He’s smelling things right now, Helen. And it’s not only what’s on the snow, it’s the air drifting past that he’s smelling. He picks up a scent quickly. But is it the right one? Oh, having a bit of a sniff here. He definitely knows there’s something here. He’s on to some scent there, for sure. His big paws are pretty efficient aren’t they? Yes.
Yes. It looks like nothing would get in his way and he’s shifting a lot of snow. Yeah. Oh, there we go, he’s got it. [Laughs] He’s got it. He found it. Good girl! Look at that. Otis, come over. And now, it’s Kensa’s turn. Kensa! Did you hear it beat? [LAUGHING] Nothing. No, nothing at all. Absolutely quiet. It’s amazing. But what have the microphones picked up? The decibel waveforms show the sound being generated by the birds in flight. Each spike is an individual wingbeat. But with the barn owl there’s almost nothing. Even our array of super-sensitive microphones failed to pick up any sound of Kensa in flight. You see the owl doing exactly the same. Nothing. Nothing at all. I’ll play it again. There’s not a sound here. Yeah. That is really impressive, isn’t it?
Yeah, it shows that they really are silent flyers. So how does a barn owl fly so silently? When air moves, it generates sound. The more movement, the greater the sound. The pigeon’s large body and small wings mean it can’t stay airborne without a lot of fast flapping. This creates turbulence in the feathers below. The peregrine has much larger wings which it uses to build up speed and chase down its prey. The barn owl is far more graceful. Kensa’s large wings and small body make it easier for her to generate lift. So just one gentle wingbeat sees her gliding effortlessly through the air; creating little more than a whisper in the feathers below.
