Do shrews echolocate?

 We know that dolphins and bats echolocate, but less is known about the ultrasonic vocalizations of other animals-- including the northern short-tailed shrew. Some suggest they don’t even make ultrasonic vocalizations at all, but instead produce noise when they move. In this episode, Valerie Eddington and Laura Kloepper (both currently at University of New Hampshire and previously at St. Mary’s College) discuss their research into the sound made by these creatures. 

Associated paper: Margaret E. Gleason, Valerie M. Eddington, and Laura N. Kloepper. "Acoustic behavior in the northern short-tailed shrew (Blarina brevicauda): Ultrasonic click production in a novel environment." The Journal of the Acoustical Society of America 154, 411 (2023); https://doi.org/10.1121/10.0020071

Read more from The Journal of the Acoustical Society of America (JASA).
Learn more about Acoustical Society of America Publications.

Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022

Transcript

Kat Setzer  00:06

Welcome to Across Acoustics, the official podcast of the Acoustical Society of America's publications office. On this podcast, we will highlight research from our four publications. I'm your host, Kat Setzer, editorial associate for the ASA. In today's episode, we'll be talking to Valerie Eddington and Laura Kloepper, who performed this research while at St. Mary's College and are now at the University of New Hampshire. They are coauthors on the article, "Acoustic behavior in the norther short-tailed shrew (Blarina brevicauda): Ultrasonic click production in a novel environment," which published in the July 2023 issue of JASA and was also featured in an AIP publishing Scilight. Thanks for taking the time to speak with me today, Valerie and Laura. How are you?

Valerie Eddington  00:51

 I'm great. How are you? 

Kat Setzer  00:52

Good. 

Laura Kloepper  00:53

I'm doing well. Thank you. 

Kat Setzer  00:54

So first, can you tell us a bit about your research backgrounds? 

Valerie Eddington  00:54

Yeah, I can start out. So my background prior to starting graduate school is mainly in animal bioacoustics and behavior. This paper specifically is a result of the first ever research project I worked on as an undergraduate when I was a sophomore in college, but since then, as an undergraduate, I did research on the alarm calling behavior of fox squirrels and I also did some behavioral work with giraffes. And now as a graduate student, I've shifted gears a little bit, and now I'm focusing more on acoustic ecology and population ecology. And I'm looking to develop models to monitor really large aggregations of colonial seabirds and bats using different acoustic methods. That's fun.

Laura Kloepper  01:42

And my background, so I received my PhD from the University of Hawaii at Manoa and I studied odontocete echolocation, so I studied the echolocation of whales and dolphins. And then I shifted gears in my postdoc at Brown University, where I studied bat biosonar. And then I continued my research with biosonar in bats and dolphins when I began working as a professor and have over the years learned to expand to lots of different animals along the way.

Kat Setzer  02:14

Including the shrew! So most people think about echolocation in terms of bats and dolphins, like you were mentioning, but other animals use it as well. Can you give us a little background on terrestrial mammal echolocation?

Laura Kloepper  02:23

Absolutely. So echolocation in its true sense, this is where it gets a little, we'll say, murky a little bit in the literature because there's a fine distinction between-- well, actually not so fine distinction-- between echoranging, which is using sound to detect objects in an environment, which is something that actually a lot of different animals are capable of doing, and I'll come back to that a second. But there's a fine distinction between echoranging versus echolocation. So bats in dolphins have been studied for decades and decades and decades, and they, we know they have a true form of echolocation. We know that based on kind of their their fine spatial resolution and how well they're able to detect objects, you know, they can detect, a bat can detect if an insect is fluttering. Some whales and dolphins can even detect what species of fish it is from the echo signature. So we know that bats and dolphins have a really fine-scale echolocation system. But we also are beginning to learn about other species that use ultrasonic signals to detect objects in their environment, which, because it has not been as well studied as often, is referred to as "echoranging" because we don't fully understand the capabilities of their echolocation or echoranging systems. So, for example, there are some bird species that live in caves, dark caves, that use acoustic signals to navigate. These are cave birds, oil birds, cave swiftlets. There's also been evidence of shrews using ultrasonic signals for navigation, as well as even most recently just a few years ago, a really nice comprehensive study came out showing a group of animals called the soft-fur tree mice that use ultrasonic signals to navigate their environment. So it's exciting, because I think we're still starting to understand, are still continuing to understand how animals are using sound potentially navigate their environment. And you know, as more and more animals use ultrasonic signals, I think that we might find more species using ultrasonic signals to navigate their environment. 

Kat Setzer  04:27

So what are the characteristics of vocalizations that are used for echolocation?

Valerie Eddington  04:31

Yeah, so there are three main characteristics that we look for in a vocalization that would signal to us that maybe this animal is producing these for echolocation or echoorientation or echoranging purposes. So the first one is we expect them to be very short in duration, either micro or milliseconds in duration, so incredibly short calls. We also expect these calls to be ultrasonic, or components of the call to be ultrasonic, meaning above the human range of hearing. So humans hear anywhere in the frequency range from 20 hertz to 20 kilohertz, although that's a little high for most people. And frequency is just the pitch of hearing. So we think of high-pitched noises, those are high-frequency noises. And so we expect echolocation or echoorientation calls to have these ultrasonic components because that helps these signals travel much faster through the environment and get back to that sender a lot faster, so they can get that information quickly. Whereas with a call that's used for communication, for example, we might expect that to be a lot lower in frequency so that they can travel further distances. And lastly, we would expect these calls to be broadband, so have energy consisting in a really large range of frequencies rather than a narrow band of frequencies.

Kat Setzer  05:58

Okay, got it. So why did you decide to look at the northern short-tailed shrew?

Valerie Eddington  06:03

Yeah, so we wanted to do the study, first of all, because the echolocation hypothesis for shrews has been up for debate in the literature for decades now, really. And recently, in 2021, there was a paper published that was kind of questioning whether these vocalizations are even vocalizations produced by the animal or if they're just byproducts of locomotion while the animals are maneuvering an environment. And so that kind of inspired us to do this study to begin with, but specifically, we chose the northern short-tailed shrew because we had them right in our backyard at St. Mary's, and it was "easy." I say that in quotation marks, because it's really not that easy to trap a shrew, but they were available to us. So we set out traps in the college woods area at St. Mary's College. And we trapped some shrew as best we could to try and make our own conclusions about shrews and the ultrasonic vocalizations they produce.

Kat Setzer  07:03

Okay, well, and so that leads into a story that you were telling us as we were preparing for this episode. And you mentioned that you had some trouble getting the shrews. So what happened?

Valerie Eddington  07:14

Oh, what didn't happen? First of all, the first time around when we were working on this part of the project, I think there was a little bit better luck, we were, although we were only able to catch four individuals. But later on as part of my senior thesis, we were hoping to continue this work. So we took to the grass and woods again to try and trap more shrews to expand on this research and didn't have the same luck. I don't know if you can call catching four shrews "luck," because that's still a really small sample size. But regardless, we were not able to catch any shrews our second time around. We had a lot of deer and raccoons and other critters that were just getting to our traps first. The raccoons were literally ripping these metal traps apart to get the goodies inside. We tried doing pit traps. So we spent, you know, a few hours a day digging holes in 90 degree Indiana summer heat (which really wasn't too bad. I'm just giving Laura a hard time) to try and catch these animals. But we did not have success the second time around. So these are certainly tricky to catch, at least where we were trying to catch them.

Laura Kloepper  08:24

And I'm gonna interrupt for a second just because I have to give credit to the team that attempted to catch the shrews because Valerie is not really giving full justice to the story and the incredible effort that these students went through. It was a team of Valerie and two other students who, you know, every day, twice a day, basically, were outside trying to set new traps and dig new traps. And they were in you know, waist-high poison ivy, full sun and day after day after day. And I think when I finally said to them, "Y'all, I think we need to call it. I think we're just not getting any shrews this summer." The look on their face was such a relief. And I think it was just a few days shortly after I was going for a run. And what did I nearly step on with my foot was a dead shrew on the sidewalkm and I said, "We've been foiled by the shrews, man." The Taming of the Whrews did not happen in the summer of 2020, I think, was it, Valerie?

Valerie Eddington  09:24

 2021. 

Laura Kloepper  09:25

That's what it was. I'm gonna blame it on the pandemic.

Kat Setzer  09:28

Yeah, they were, you know, they were social distancing as well. So, tell us a bit about the setup for analyzing their actual vocalizations.

Valerie Eddington  09:40

Yeah, so after we were successful in trapping a shrew, we would bring it into the lab, where we had our experimental chamber setup for these recording sessions. We recorded each shrew for two 10-minute recording periods, and we did this in just an empty plastic container. Prior to recording, we withheld food for an hour to induce exploratory behavior and hopefully get them to produce more of these vocalizations as if they were foraging, for example. And so we recorded ultrasonic acoustic recordings during this time, as well as video recordings that looked down on the shrews so that we could see the motion of their head if they were moving it back and forth, doing what we call "scanning behavior," or simply if they were moving, or if they were not moving.

Kat Setzer  10:30

Okay, cool. So then you have these recordings of the shrew vocalizations. So how do you assess what the shrews were actually using them for?

Valerie Eddington  10:38

Yeah, so once we had those recordings, we looked at three main things. The first thing we did was just extract all of the ultrasonic clicks we could find present in the recordings, and we call these "click trains." And then, from these time periods where they were emitting these click trains, we looked back at that video, and we looked at their behavior while they were producing these clicks to see if they were moving, if they weren't moving, and we also looked to see if they were exhibiting any head-scanning behavior, which is something we see commonly in other echolocating animals like bats. They do this while they're emitting these ultrasonic clicks. So we looked at that. And then lastly, we pulled out what we consider to be really high-quality clicks. So these are clicks, that had a high signal-to-noise ratio, meaning they were a certain degree louder than the environment. And so these clicks were more likely to be a true example of what the calls looked like, because they were likely produced in close proximity to that microphone that we had set up to record these vocalizations. And with those high-quality calls, we look to see what the characteristics were. So again, we were looking, are they broadband? Are they shortened duration? And do they have peak frequencies in the ultrasonic range?

Kat Setzer  11:54

So what did you end up learning about shrew vocalizations?

Valerie Eddington  11:56

Yeah, we learned that shrews produce ultrasonic clicks when they're moving and when they're not moving. So they are not simply a byproduct of locomotion. These are vocalizations animals are producing. And we also learned that when they're producing these clicks, they're often exhibiting that head scanning behavior I mentioned. And then importantly, we found out that these are short-duration, broadband clicks that have peak frequencies in the ultrasonic range, like we see and other echolocating are echoorienting animals.

Kat Setzer  12:29

Okay so they may possibly echolocate.

Valerie Eddington  12:32

 Yeah.

Kat Setzer  12:33

But unclear. 

Valerie Eddington  12:33

Yeah.

Kat Setzer  12:34

Okay. So do you have any future plans related to shrew vocalization research?

Valerie Eddington  12:40

Yeah. So as I've mentioned, we did attempt to continue this research as part of my senior thesis in my undergrad in 2021. But we were very unsuccessful in our trapping effort that time around. But we do have the experimental chambers for the next part of this experiment ready to go. So if there is ever a really eager, undergraduate at the University of New Hampshire who wants to come tackle this project, and try and trap some shrews, I would love to continue it. I just I do not plan to continue as part of my graduate work.

Kat Setzer  13:15

You don't want to spend all of your time digging holes.

Valerie Eddington  13:18

I really don't. Yeah, but I'd be happy to help someone else do it.

Kat Setzer  13:21

That is fair, understandable. So you know, I have to say I do admire your determination and perseverance  when trying to capture the shrews for your research. Abd now we may know that possibly those shrews in our yards could be echolocating! Or it seems like they might be. So thank you again for taking the time to speak with me and I wish you the best of luck in your future shrew and non-shrew related research.

Valerie Eddington  13:44

Yeah, thanks so much for talking with us. 

Laura Kloepper  13:46

Thank you.

Kat Setzer  13:49

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