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2015 Field Season: Expanding the boundaries of bat-insect field recording

Posted by Aaron Corcoran on July 31, 2015 at 1:10 AM Comments comments (14)

I just got back from conducting field research on bats and insects at the Southwestern Research Station, my seventh summer in a row conducting research there. There are many reasons I keep going back. The station is home to one of the most diverse communities of bats and moths in North America. There are world-class field courses on both taxonimic groups, and I've been involved with both courses, one as an assitant, one as a guest lecturer. This diversity ensures I won't run out of animals to study any time soon. I also have at my disposal a small army of eager volunteers, ample lab space, a workshop where I can build anything I might need, three meals a day (lunch, dinner, and second dinner), and a community of researchers, volunteers, and staff that eases the burdens of long nights that seem to stretch one into the next.

Volunteers Theo, Julia and Alexa sort insects in the lab. My assistant Orion pretends to eat a sphinx moth

For several years now, I've been developing a field-recording setup for capturing bat-insect interactions on multiple video cameras. I can then use these videos to reconstruct the flight paths of predator and prey in 3-D. By 2011 I had refined the system to be able to capture volumes of about 125 cubic meters, or about half the size of a racketball court. I considered this quite a feat, but the system had limitations. I was able to document predatory events of bats that attack insects close to the ground, such as Myotis bats. However other species, such as Mexican free-tailed bats, fly exclusively in the open, far off the ground and outside the view of my cameras.

This summer I deployed the next version of this setup involving four sets of high-resolution infrared cameras and high-power infrared lights. With our new apparatus we can capture volumes of 1000 cubic meters or more. In other words, we can detect and reconstruct the precise 3-D position of a small moth anywhere within a volume the size of half of a basketball court and up to three times the height of the basket. Each night is a bit like setting up for a rock concert. In the event of rain (we work in the monsoon season) we race frantically to unplug and then cover all the equipment, letting it dry throroughly for at least 24 hours before plugging it back in.

Time-lapse photo of field recording setup, including three cameras and IR lights, and an ultraviolet light to attract insect activity. Traces of bats and insects can be seen in the night sky.

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In order to use videos from multiple cameras to reconstruct flight paths in 3D you need to know the exact positions, orientations, and specifications of your cameras. Fortunately there is now software available that allows you to derive this information through a process called 3-D calibration. Ty Hedrick at UNC and his colleagues have done a great service to science by developing this software and making it freely available. It works better than software I had paid thousands of dollars for, which I've now completely discarded.

To calibrate my cameras in the field I use a method called "Wand Calibration", where two markers fixed at a specific distance are moved in front of the cameras. Traditionally this is done by fixing two objects to the ends of a rod, or "wand". Previously I did this with an 8-foot rod mounted to a 16-foot painter's pole. This turned into what looked like an odd form of interpretive dance, and a sweaty workout. Even more of a problem was that I was limited to calibrating volumes I could physically reach with my calibration device. To calibrate cameras for 3-D reconstruction of high-flying bats and insects, I needed a new method. Enter the drone.

Field 3-D calibration kit, including UDI 818A quadcopter, IR-tape-covered wiffle balls connected by fishing line, water-baloon catapult launcher, and baseball covered in IR tape.

By drone, I mean toy quadcopter. It's amazing what $50 and some YouTube "Mods" will do, including removing the plastic protective cover and camera and attaching an anchor to tow whiffle balls covered in IR tape (OK, I didn't find that last part on YouTube). The trickiest part was finding objects that were heavy enough to ensure a taught line, but light enough that the quadcopter could pick them up. In the end my calibrations appear to be coming out alright (see image below), so I think I found a solution that works. The water-balloon launcher lets me send the IR baseball 100 feet into the air, a necessary step to determine the axis of gravitational acceleration (i.e., what's up). 

Here is the output of the 3-D calibration showing the track of the markers towed by the drone, the ball launch, and the positions and orientations of the cameras:

It's way to early to be publicizing results, but I'm already seeing what looks like some fascinating foraging behavior by Mexican free-tailed bats. Here's a sample:

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Perhaps most exciting is what lies ahead. We now have the technology to capture behavior of wild, freely-behaving bats and insects in large volumes and in spaces untethered to the earth. Oh yeah, and we have drones.

Interview for Today's Science

Posted by Aaron Corcoran on December 25, 2014 at 7:00 PM Comments comments (3)

I recently had the good fortune of being interviewed by Today's Science, an online distributor of educational materials to high-school and college students, for their series Conversations with Scientists. We talked about how I got interested in science, what it is like being a practicing bat biologist, and my recent article on bat jamming. The article is re-printed below (with permission).

“Aaron Corcoran: A Passion for Bats.” Today's Science. Infobase Learning, Dec. 2014. Web. 24 Dec. 2014.

Aaron Corcoran: A Passion for Bats

Aaron Corcoran has been a postdoctoral scholar at the University of Maryland in College Park since June 2013. He earned his bachelor's degree in wildlife in 2003 from Purdue University in Lafayette, Indiana and received his master's degree in biology in 2007 from Humboldt State University in Arcata, California. From 2007 to 2008, Corcoran was a research analyst and lecturer at Humboldt. He completed his Ph.D. in biology in 2013 at Wake Forest University in Winston-Salem, North Carolina.

Corcoran is a "scientist and educator specializing in ecology, evolution and behavior." He draws upon "a technical background in [both] computer science and biology to understand complex behavioral interactions in animals that are traditionally difficult to study (particularly bats and moths)."

Below are Aaron Corcoran's December 8, 2014 responses to questions posed to him by Today's Science. Some of the questions deal with how he became interested in science and began his career in behavorial ecology while others address particular issues raised by the research discussed in Bats Breaking Bad.

Q. When did you realize you wanted to become a scientist?

A. I became a scientist despite my best intentions not to. After studying wildlife biology at Purdue University, I worked for a couple years as a field biologist, which I loved. I spent a lot of time catching little furry animals in small traps, and tracking coyotes and deer through the Montana mountains. But I couldn't pass up an opportunity to study bat echolocation for a master's degree. Once I started doing my own research, I was hooked. There's nothing like the thrill of being the first person ever to discover something, no matter how big or small that finding might be.

Q. How did you choose your field?

A. Me and bats are a natural fit. I've always been curious about how animals behave, especially mammals. And my background in computer science (my first major in college) allowed me to study these animals that without technology are crazy difficult to study. Think about it, bats fly in the air where we can't normally go, are active at night when we can't see, and make sounds we can't hear. But there's a real thrill of unraveling the mysteries about how these animals work.

Q. Are there particular scientists, whether you know them in person or not, that you find inspiring?

A. There are many. But the scientist who inspired me the most was my Ph.D. advisor, Dr. William Conner at Wake Forest University. He taught me how to do science, how to think clearly, how to decide what questions are worth pursuing and how to make my research interesting to others. All the while, he treated me like family.

Q. What do you think is the biggest misconception about your profession?

A. Perhaps that we already know everything. I'm amazed on a regular basis to discover all the things we scientists don't know. We're brought up to think everything is known — just read a textbook. But as you learn more about any subject, you soon find the edge of human knowledge. And when you get to that point, you can start to think of really cool experiments to push that edge just a little farther for everyone else.

Q. Did the abundance of prey have any impact on whether bats resorted to jamming other bats — for example, if there were a lot of insects around, did they not bother?

A. This is actually the basis of one of the projects I'll be working on starting next summer. At this point we don't know, but I suspect the number of bats around and the number of insects around both play an important part in when bats compete for prey by jamming each other.

Q. Do bats jam other bats’ echolocation so that the potential prey will be available to them as food, or are there any other explanations for this behavior that you considered?

A. That appears to be the reason why they do it. Right after jamming a competitor, the jammer bat flies over to where the other bat was hunting and tries to capture the insect. Often what happens next is the bat that got jammed becomes the jammer and they go back and forth until one of them gives up. It's basically aerial warfare.

Q. Your study notes that Mexican free-tailed bats “form the largest known colonies of any active sensing animal, with some caves housing more than one million individuals.” Do you think the jamming behavior is related to this high population density?

A. It makes sense that the two things are related. Some bats live with up to a million other bats, which means that they have to compete with a million other bats to find food. So it makes sense that they would evolve sophisticated ways of competing with other bats.

Q. Where do you spend most of your workday? Who are the people you work with?

A. Nine months out of the year I'm working on a computer, either analyzing video and sound recordings of bats or writing papers and grant proposals. The other three months I get to be outside staying up all night while I study Bats.

Q. What do you find most rewarding about your job?

A. There are two things about my work that I find most rewarding. The first are those eureka moments when I've discovered something new or found evidence I've worked years to attain. The second are those times when I get to share my research with people in person. It keeps the research fresh for me to open people's eyes to the wild world of bats.

Q. What has been the most exciting development in your field in the last 20 years? What do you think will be the most exciting development in your field in the next 20 years?

A. Technological advancements have revolutionized biology in so many ways. Recently and for the first time, scientists have been able to film bats (and their insect prey) in the wild with multiple infrared cameras and later map their flight paths in 3-D. Just this year we're seeing scientists mounting miniature GPS units and miniature microphones on wild bats to track their nightly forays and record all the sounds they make and hear. I think that this technology alone will really change our understanding of how bats behave in the wild. And there are many other emerging technologies.

Q. How does the research in your field affect our daily lives?

A. Discovering the wild ways of foreign critters is like exploring another planet or an alien life form. I hope that when people learn about something like bats jamming each other's echolocation, it opens their mind to something they've never even thought about. In a small way, that can ignite a person's curiosity about the world around them. Curiosity and knowledge are powerful things.

Q. For young people interested in pursuing a career in science, what are some helpful things to do in school? What are some helpful things to do outside of school?

A. First, follow your passion, even if you don't know why it's your passion. If you care deeply about something, you'll find a way to make it part of your life. And with patience, you'll get good at it. Second, find people who can guide you and who care about you. Usually those two things go hand in hand, because when someone sees another person truly following their passion, they want to help them reach their potential.

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International Bat Research Conference 2013 Costa Rica

Posted by Aaron Corcoran on August 19, 2013 at 4:00 PM Comments comments (14)

The largest-ever gathering of bat biologists occurred  last week in San Jose, Costa Rica at the joint meeting of the 16th International Bat Research Conference and 43rd North American Symposium for Bat Research, with 639 people from 55 countries attending, and I was fortunate enough to be present.


There was some wonderful conservation-minded research on white-nosed syndrome and bat mortalities caused by wind turbines. It's becoming increasingly clear that Pseudogynoascus destuctans (the cause of WNS, formerly Geomyces destructans) is an invasive exotic species brought over from Europe by humans. Pd is widespread in Europe and bats there do not show the mass mortality seen in the US and Canada. Sebastian Puechmaille from University College Dublin presented work modeling the habitat occupied by Pd in Europe and used those models to predict where Pd might occur in North America. The sad news is that we should expect it to eventually cover most of the northern half of the US and nearly all of Canada. People are still nowhere near a real solution to one of the biggest wildlife disease epidemics ever reported.


As for wind turbines, people are starting to find ways that turbines can coexist with bats, at least with fewer mortalities than we have seen. Michael Schirmacher from Bat Conservation International presented a summary of around ten studies that have tested whether you can limit bat mortalities by not running wind turbines at low wind speeds, when bat deaths are most common, and energy production is low. All studies found a reduction of mortality, with most showing 50% or fewer deaths at a cost to the companies of only 1% of their profits or less. Now we just need wind companies to start implementing these strategies, something that may require legislation to happen (imo).


                A presentation at IBRC 2013

I was most excited to see the 20 or so studies that related to bat echolocation. Here are some of my favorites.


Arjan Boonman from Tel-Aviv University, Israel has documented multiple unrelated species of fruit bats (Pteropodids, also called flying foxes) that apparently echolocate. While all micro-bats echolocate, it was thought that only one genus of mega-bats echolocate. However this work hints that all bats may use sound for sensing the environment, and the type of echolocation used by fruit bats -- tongue clicking -- may have evolved first, as it is simpler to use. This work, when fleshed out, has the potential to dramatically change our understanding of echolocation in bats.


Klemen Koseij from the Max Planck Institute of Ornithology in Germany provided compelling evidence that bats are able to use echoes from sounds made by other nearby echolocation bats to detect objects. It's been shown by other researchers that big brown bats competing for food in captivity sometimes go silent while following other bats. But are they simply localizing the sounds of the bat they are following or are they also able to get information from the other bat's echoes? Klemen devised a clever experiment to test this involving placing two bats in a square-shaped bat race track. When the leading bat turned one of the corners and tripped a light sensor, Klemen made it such that an object (a frisbee actually) was triggered to move rapidly over a short distance towards the leading bat. This caused the bat to turn sharply away from the object. The interesting part, however, was what the trailing bat did. It too maneuvered away from the object, even though it was trailing around the corner and likely could not see or echolocate the frisbee. Klemen reasoned that the only way the trailing bat could detect the object was by hearing an echo from the sound the leading bat made that reflected  off the moving frisbee. If confirmed, this study demonstrates a previously unknown ability in echolocation animals.


                        Friends wearing bat noseleafs at the banquet

Advancements in technology have brought about a revolution in bat studies over the last ten to fifteen years. Yossi Yovel, also of Tel-Aviv University, proved that those advancements are continuing by being the first to put an ultrasound microphone that records to a data card and a GPS on a free-flying 30-gram bat. This allowed him to make all-night recordings of bat echolocation emissions and tracks of their flights as they foraged, interacted with other bats, and searched for insects. The possible applications of this technology are sure to open many windows into the amazing capabilities of bats.


Finally, I was very impressed by Caroline and Michael Schoner's presentations (Ernst-Moritz-Arndt University, Germany) on the symbiotic relationship between Harwike's wooly bat and the pitcher plant Nepenthes hemsleyana. This pitcher plant has evolved mechanisms to attract Harwicke's wooly bat to roost in its "pitcher", thereby providing good conditions for the bat to roost (as detailed by Caroline) in exchange for nutrient-rich bat guano. This pitcher plant has evolved to reflect a distinctive echo to the bat from a structure just above the pitcher. When Michael experimentally modified this structure to make it reflect stronger or weaker echoes, bats were not attracted to roost in the modified plants, but instead the unmodified plants with their charachteristic echo (which Micahel was able to characterize with a robotic echo-locating machine). These studies and many others at the conference continue to show how intricately bats are connected to ecosystems and the many benefits they provide.


This conference was extremely gratifying to me both personally and professionally. I met several biologists whose work I strongly admire and cemented dozens of relationships with colleagues that I've met over the years. When I multiply my experience, the knowledge I gained and relations developed by 639 I gain a true appreciation of what was accomplished at this meeting.

Filming Micro Monsters 3D

Posted by Aaron Corcoran on January 11, 2013 at 4:30 PM Comments comments (6)

I'm on a plane on my way back from London, England  to Trinidad, California (my home for the spring), finishing what will be 42 hours of travel time for 44 hours in London. I just finished being filmed talking about my research on sonar jamming moths for an upcoming series, Micro Monsters 3D, featuring David Attenborough (no, to my chagrin i did not get to meet him). The nature documentary will be on 3d tv channels and IMAX theaters at certain locations around the world. Yes, that means if you are in one of those locations you will likely be able to see me in full 3d on IMAX. That's kind of a scary thought, and it was the absolute last thing I'd let myself think about while being filmed yesterday for about 8 hours (which I'm guessing will turn into 2-4 minutes of screen time with the high-speed video of bats and moths I provided added in). I had to wait in the morning while the crew filmed a wasp capturing a roach, laying eggs in the roach's body and and dragging it into a hole to bury it (this is called egg parasitism and a large wasp called a tarantula hawk does the same thing to tarantulas). The wasp's eggs will hatch days later and then feed on the still living body of the roach. Apparently the crew had been trying to film this a whole day before I arrived without luck. This morning however, the wasp was ready. I didn't get to see much of the footage, but I could see a large widescreen 3d television showing a live feed of the set. With my 3d glasses on I caught a glimpse of the wasp emerging from the hole where it would soon bury its roach. It was like I was looking straight down on the scene with my head inches from the wasp. The ground alone was fascinating enough that I spent minutes examining each bit of leaf, twig and seed that protruded from the intricate texture of the soil. I hadn't seen 3d video like this since watching the Avatar movie.


This was the same level of detail that would soon be captured of me, explaining the extraordinary adaptations of moths evading hungry bats. In the studio (one that neighbored studios where Bond movies and Harry Potter were shot) they had constructed a highly detailed biology office. My office.

"My" office for a day. Looks pretty real doesn't it?


My desk had two large monitors much like the ones in my real office. Between and around them was clutter galore -- bits of electronics, microphones, audio mixing equipment, used coffee cups and coffee stains and a custom notebook that I happily filled with research notes (for a page at least). Some of the details around the office were uncanny. Reel-to-reel audio tapes just like the ones my PhD advisor recorded moth sounds on two decades ago and still has laying around the lab, an oscilloscope just like the one in my office cabinet, a 10-foot fishing pole that reminded me of one that I had used for dangling moths from a line to entice attacking bats. This was 'my' office, at least for a day. This was a good thing, because as I sat at my office operating familiar programs for visualizing sounds and playing high-speed videos of bats and moths on the two computers, I could almost forget that around me a dozen people including a cameraman, Albert the  sound guy, two producers Tim and Paul, and several support staff, were all watching me. Not to mention the lights, boom mic, and giant 3d camera on a crane that was sometimes brought to what seemed like inches from my face. But those things were imaginary. This was just another day at the office. I just happened to have a visitor (Tim, the main producer) who was very curious about my work, and I was showing him my clips and telling him about a great mystery to science I and my colleagues eventually figured out. This visitor just happened to stay in my office all day and kept telling me how I could say what I was saying in an even more clear and concise fashion.

Breaking down the set minutes after wrapping up

Amazingly, the day flew by. My cold that had me talking like a frog in the morning cleared out of my throat in time to talk on camera. My anti-jet lag diet of the last four days had worked and I felt reasonably refreshed despite an eight hour time change. On the spot and with the help of Tim, I was able to describe the story of discovering  sonar jamming. I flubbed my lines my fair share of times, but somehow I got through it. Next thing I knew we were done and they were tearing down my office to turn it into a set for a mock autopsy that would be done the next day. And I was hopping on a train to downtown London to sightsee and get fish and chips and a pint for a few hours before catching some sleep and a flight, where I am now. And a part of me cant help wonder, was all that a dream? Did I fall asleep in my office and imagine all those people and lights? I guess in about nine months I may be able to go to an IMAX to find out.