Attaching a directional microphone to a Wildlife Acoustics ultrasonic recorder?

Luke Quarles

@lukequar
| he/him

I am a PhD student at the University at Buffalo, studying the endangered slow lorises (Nycticebus spp.) of Thailand. Presently, my work focuses on studying the ultrasonic vocalizations of slow lorises and testing out passive acoustic monitoring methods for these cryptic primates.

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Acoustics

Background: I am still new to acoustics research and I am hoping to get some advice on integrating a directional microphone with an ultrasonic recorder. I am trying to collect acoustic data from small, nocturnal, and arboreal primates (both sonic and ultrasonic calls). I want to connect behaviors with vocalizations so it is crucial that I am able to say that my focal individual is the one producing the call.

Query: I want to use a Wildlife Acoustics Song Meter Mini Bat 2AA, since I have used it before for PAM, but I am trying to find a way to make it directional instead of omnidirectional. Does anyone have any experience with or suggestions regarding attaching a directional microphone to a Song Meter Mini bat recorder?

Any and all information would be greatly appreciated! Thank you so much!

Jesse Turner

@jcturn3 | He/Him

Colorado State University

I am a graduate student at Colorado State University working to develop novel acoustic technology for remotely monitoring wildlife.

30 April 2024 4:28pm

Hi Luke, sounds like an interesting project! One thing to note is the ultrasonic Wildlife Acoustics unit you're looking at is already fairly directional. Take a look at the horizontal directionality plot towards the bottom:

You can see that for the relevant frequencies for slow lorises ultrasonic calls (40-60 kHz), there is 25-30 dB difference between 0 and 180 horizontal degrees. It's not perfect, but is close to some directional mics, and if it works well enough for your project it would save a lot of time and testing!

If you do choose to integrate an external directional microphone, be careful with microphone placement to avoid potential ultrasonic reflections from any hard flat surface like a tree trunk, water surface, or the instrument housing itself. Here's an example of some echo calls from reflective surfaces from bat vocalizations:

It would be helpful to hear how you plan on obtaining behavioral information (and what kind) to correlate with vocalizations? Observations, cameras, biologgers, etc.? This could inform responses a bit more.

Luke Quarles

30 April 2024 4:28pm

Hi Jesse,

Thank you so much for your reply and for the fantastic knowledge and resources! I was unfamiliar with the plots, so thank you for providing some interpretation- I will have to work to better understanding them. This may change things (I was going off of experience from field work with the last iteration of this WA recorder which had omnidirectional recording) and I may choose to pilot the recorder without an external microphone this summer.

Regarding my plan for collecting behavioral data, I plan to follow 15 wild individuals in a reserve in Thailand (mostly dry evergreen and dry dipterocarp forest with some human modified areas). I intend to use instantaneous focal sampling to observe lorises in two shifts between 18:00-06:00h. During these focal follows I will record all behaviors at 5-min intervals and use all-occurrences sampling for social and feeding behaviors, using an established slow loris ethogram. Simultaneously, I plan to record vocalizations, with the help of a research assistant and field guide. So we will be carrying the recorder with us during behavioral data collection. I intend to match up the timestamped loris vocalizations with the behavioral data to understand the call's function.

Jesse Turner

30 April 2024 4:28pm

If you have the resources, I would suggest testing the sensitivity and directionality of the system at relevant frequencies both with and without an external mic, and let the results dictate which will be best for your case study.

Another thing to think about since you are manually taking the recordings is if a WA unit is really necessary. You're paying for the technology of a remote system without needing it. Other cheaper handheld recorders (such as Zoom recorders) could free up $$ for a higher quality directional microphone. Although of note is that common Zoom recorders like the H4n only sample up to 96kHz for which the upper frequency limit (48kHz) is getting very close to the frequencies you're likely wanting to measure.