Swamp lights and bat sight

[MUSIC] Welcome to Science Sessions, the podcast of the proceedings of the National Academy of Sciences, where we connect you with Academy members, researchers, and policy makers. Join us as we explore the stories behind the science. I'm Paul Gabrielson. And I'm Matthew Hardcastle. In honor of Halloween, we'll be exploring two spooky mysteries in this special episode. Bats are often incorrectly thought to be blind, but these flying mammals possess functional vision systems, despite their nocturnal lifestyle and echolocation abilities. In a recent PNAS article, researchers used bat-born recorders to explore how the animals might integrate multiple senses while hunting. Keeping with the theme of the spooky season will also learn in this episode about a plausible origin for the ghostly will of the wisps. For centuries, people around the world have reported mysterious flickering lights in humid or swampy areas. They go by many names, including will of the wisps. It's well known that organic matter decomposition creates flammable gases in swamps and bogs. But what could ignite the will of the wisps? In a recent PNAS study, Richard Zare of Stanford University and colleagues explored how a surprising energy source might ignite the spooky swamp lights. Richard, have you ever seen will of the wisps in the wild? I wish I had. I have not. What did we already know about will of the wisps before your study? Today we know pretty much that it's related to swamp gas of some sort or another, but there's been a mystery what makes it ignite. We know if you take a match, that's easy, but where's the match? They know that the swamp gas is mostly methane and it contains a little bit of what's called phosphine, pH3, a phosphorus compound. But that doesn't easily combust by itself. And if you do make it combust, it tends to have a green flame. And what we see is really blue. So it's not clear that it's that. People have said, "Well, it must be static electricity, but in wet places you don't have static electricity. Along the go, Volta for Italy, for which the Volta is named, he says, "Ah, it's due to lightning. I think he had the right explanation. It's micro lightning. And the micro lightning is coming from obviously charged droplets that get close together in a spark jumps from the negative smaller droplet to the larger positive droplet. And this spark triggers the combustion, the oxidation of methane to make a cool flame." How could water droplets ignite methane? There's actually a huge difference between water and water droplets. Water's neutral, water's benign, but water droplets are highly reactive. And it has to do with the interface. When you have the water-loving hydrophilic material touching the water-hating hydrophobic air, you develop a very large electric field at the interface. The little droplets get negatively charged. Bigger droplets are left behind, positively charged. Water starts out as neutral. Now you have positive and negative things. And when they snuggle close to each other, bang, zap, we get micro lightning. Tell us about the methods of your study. How did you explore this phenomenon? By using instrumentation, using a photon counter, a photo multiplier, or using a high speed camera. My postdoc, Yusha, was able to actually record this. You can actually see the small flashes of a lightning between droplets. Their porous material is a bubble stone that allows you to put the gas through containing methane and mixture through water. And then the bubbles, of course, rise. They're lighter than water. And they come to the top of the surface and they burst. The light is being emitted not inside the water. It's being emitted at the top of the water and beyond when it sets things off. I've seen it also using hydrogen. You don't have to have methane. Methane is not what makes it happen. What are the broader implications of your findings beyond just will of the wisps? I think you can get chemical reactions at these interfaces. And so for example, we have found that we are able to turn nitrogen into ammonia. We do that at room temperature. And prior to this, the famous Haber Bosch process has been used to make ammonia. And that requires high pressure and high temperatures. And it's hard to do. Whereas what we can do is relatively simple. This could be the answer to how we get building blocks of life on early earth. You can't have life as we know it without carbon nitrogen bonds. So where did they come from? Long ago, Miller and Yury said, oh, they come from lightning. We have found since and published that to spring water droplets into that mixture of simple gases leads to all the same results that Miller and Yury saw. Water sprays are much more ubiquitous found many more places than lightning. What are the caveats or the limitations of the study? For me, the biggest limitation to make this practical is how do we scale this up? Because I really want to be able to do things like make ammonia from it. And so they're now we are facing big engineering challenges and they haven't been done yet. From mysterious lights, we return to the question of bat vision. The flapping of wings in the dark may elicit dread for some, but bats provide a variety of important ecosystem services, including pest control. Laura Stitzholt, a biologist at Arhus University in Denmark, and her colleagues explored how common and notchal bats might use vision to enhance their hunting success in dynamic environments. Laura, what can you tell us about the species you studied? We studied the common and notchal bats, which is a very large and fast flying bat species. We were lucky to study them in the middle of Berlin, where they are living in small bat boxes where we can get access to them. Because they are commonly found in cities, they are light tolerant species, you can say. What instruments did you attach to the bats? The track us we attached to the bats are tiny backpacks with a miniature microchip inside and it has an ultrasonic microphone that can record the echolocation behavior of the bats. So all the sounds that they are meeting into their environment and all the echoes that are coming back. Then they also have some different sensors in them that we also find in our smartphones. For example, a step count at that count how many steps we take that can tell us about their wingbeats, how often do they flap their wings and how strong are their wingbeats. And then we have a light sensor in it as well that can record the ambient light level so we can combine all of this information into one and get a very nice picture of what the bats are doing. How did the bats echolocation behavior compare in dark versus lit environments? When the bats were flying from the roost to their origin grounds, we could see that they were using the same echolocation behavior both when it was stuck and when it was light. The picture changed when we looked into the prey tracking. When they are attacking prey, they are emitting these echolocation calls that are gradually increasing in repetition because they want a faster update rate of their environment when they are doing these tracking of prey. When they do that in the darkness, it sounds like this file. An ample light level for the bats. It sounds differently. What you can hear in the audio file is that they are calling with longer intervals between so they would call less frequently and get less information from their environment. But at the same time, they would approach their prey much faster. It could show us that they are supplementing their central information with vision. What do the results suggest about the benefits of integrating information from multiple senses while hunting prey? Our results suggest that getting information from multiple sensory systems at the same time. In this case, it can contribute to a better decision making for them so they can make a faster prey tracking with more powerful flights. This is the first time this has been shown in a predator in the wild. We know that predators most likely are using several senses if you have a shark that's going for a prey in the open ocean. They will use their smell, for example, to smell the blood and they will use vision to strike actually proving it is difficult because predator prey interactions usually take place on very rapid timescales and it's even more so difficult to study the senses that I involved in these processes. What do the results imply about the potential impact of artificial light on bats? Even though this study could show that they are attacking insects faster in light, it could be a good thing for bats, but it really is not in the sense that artificial light is never a good thing for bats. Bats occupy 20% of mammalian biodiversity, but about a third of the batch species we know are vulnerable and they are under threat from many different things. A lot of them are human activities and light pollution is one of the big factors. We can see that if there's light in an area where they're roosting, they may abandon roosts and they prefer to fly in dark corridors in cities. So it's important to mitigate light pollution both in the cities and also in critical bad habitats. Halloween is a time of mystery, but as we've heard from these examples of hunting bats and ghostly swanflights, exploring unknowns in the natural world can lead to new scientific knowledge. Thanks for tuning in to science sessions. You can subscribe to science sessions on IT. 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