Froggy camouflage handheld fans

Project by Anna Carreras. BAU Design College of Barcelona, Spain.

Hand fan (abanico) inspired by a glass frog. Photo by Anna Carreras. Gamboa, Panama.

Rainforests of Panama are some of the world’s most biologically diverse areas. Animals use camouflage tactics to blend in with their surroundings, to disguise their appearance. They mask their location, identity, and movement to avoid predators.

By the other hand in cities in many countries the increased use of surveillance technologies have become part of the public and private landscape. Citizens lack of camouflage tactics to avoid these forms of elevated vigilance. Can we learn and borrow tactics from animals to keep away from this constant monitoring?

The froggy camouflage handheld fans project proposes a playful way to act upon our surveying world while learning from frogs camouflage in Gamboa rainforest, Panama.

Hand fan inspired by a dart frog. Photo by Anna Carreras. Gamboa, Panama.

Nature in Gamboa

Exploring nature, animal watching in Laguna Trail. Photo by Marta Verde. Gamboa, Panama.

Attending the Digital Naturalism Conference (Dinacon) from August 26th to September 1st offered the possibility to do several exploratory walks around Adopta un Bosque station, La Laguna trail in Gamboa and Pipeline road on the border of the Soberania National Park. Animal watching includes birds (thank you Jorge), frogs, mammals and several butterflies and insects.

Bat sleeping place near the Panama Canal. Photo by Marta Verde. Gamboa, Panama.

A species’ camouflage depends on the physical characteristics of the organism, the behavior of the specie and is influenced by the behavior of its predators. Background matching is perhaps the most common camouflage tactic and animals using this tactic are difficult to spot and study. Another camouflage tactic is disruptive coloration that causes predators to misidentify what they are looking at. Other species use coloration tactics that highlight rather than hide their identity. Warning coloration makes predators aware of the organism’s toxic or dangerous characteristics. This type of camouflage is called aposematism or warning coloration.

Animals with different camouflage tactics. Photos by Mónica Rikić, Marta Verde and Tomás Montes. Gamboa, Panama.

Studding camouflage tactics includes animal observation and some readings. Frogs are easier to spot and photograph in Gamboa than insects or snakes. The animal books at Adopta un Bosque station and Dinalab gave the opportunity to classify the different species and gain some knowledge about their colors and skin patterns.

Frog spotted and photographed during Pipeline road walk. Photo by Tomás Montes. Gamboa, Panama.
Frogs spotted and photographed during walks. Photos by Tomás Montes, Päivi Maunu, Jorge Medina and Tomás Montes. Gamboa, Panama.
Frog identification triptych at Dinalab. Photos by Anna Carreras. Gamboa, Panama.
Frog identification book at Adopta un Arbol station. Photos by Anna Carreras. Gamboa, Panama.

Patterns

Different frog skin patterns generated mathematically. Images and code by Anna Carreras.

The skin of some animals show a self-ordered spatial pattern formation. Cell growing and coloration creates some order resulting from the specific differentiation of cell groups. In such complex systems cells are only in contact with their closest neighbors. Which are this morphogenesis mechanisms where some order emerges from individual cells? Which are the mathematical models we can use to achieve this kind of growing patterns and gain some knowledge about them? Can we simulate some frog’s skin visible regularities with a coded system?

The mathematician Alan Turing predicted the mechanisms which give rise to patterns of spots and stripes. The model is quite simple, it places cells in a row that only interact with their adjacent cells. Each cell synthesizes two different types of molecules. And this molecules can diffuse passively to the adjacent cells. The diffusion process makes the system and the whole result more homogeneous. It tends to destroy any ordered structure. Nevertheless the diffusion process with some interaction by the cell molecules drives to macroscopic ordered structures. The mechanism is called reaction–diffusion system. It drives the emergence of order in a chaotic dynamic system.

Steps of a reaction-diffusion model evolving from chaotic randomness to structured patterns. Images by Anna Carreras
Steps of a reaction-diffusion model evolving from chaotic randomness to structured patterns. Images by Anna Carreras.
Steps of a reaction-diffusion model evolving from an organized grid to emergent patterns. Images by Anna Carreras.

Code and interface

Frog pattern generator using a reaction-difussion system. Image and system by Anna Carreras.

A system using the Gray-Scott model and formulas was coded in Processing language. The interface shows the animation of how a frog skin evolves. The GUI also shows the system values that lead to that skin pattern formation. These values and two selected colors generate a unique frog pattern each time the system is started. The spatial feeding system options and the values that can be selected and adjusted are inspired by Gamboa’s frogs. They derive from the observed and photographed species and from the consulted books.

Frog pattern generator using a reaction-difussion system with random feeding. Image and system by Anna Carreras.

Camouflage DIY hand fans

Two different hand fans. Photos by Anna Carreras. Gamboa, Panama.

Frog skin images are used to create light folding hand fans. They are suitable for Gamboa’s hot weather and help to camouflage inside the rainforest. They can easily be taken home and used around the world in several cities.

To build the hand fans two parts are needed: the fan frame and the fan leaf. The designed DIY hand fan is designed as a traditional Spanish hand fan. The frame structure is made of a thin material that can be waved back-and-forth, birch tree or pear tree wood.

Traditional Spanish hand fan structure for laser cut. Designed dxf file by Anna Carreras.

The produced hand fans use 0.8mm thick birch wood to make sure it can bend without breaking. The fabrication starts laser cutting the 16 fan ribs for the frame and printing the camouflage image. Cut the fan leaf, using scissors, as a half circle measuring 210mm the exterior radius and 95mm the inner radius.

Laser cutting the hand fan ribs structure. Photo by Anna Carreras.

When the parts are ready put together the 16 fan ribs, one wide rib at the beginning and one at the end. Fix the fan ribs with a m3 screw and nut, a metric screw with nominal diameter of 3mm or 0.12in. Extend the fan ribs as an opened hand fan. Glue the fan leaf on the thiner exterior part of each rib and allow the glue to dry. Finally, one rib at a time, put it above the previous ones and fold the paper carefully to create the folding shape.

Hand fan in action. Photos by Daniëlle Hoogendijk and Anna Carreras. Gamboa, Panama.
Resulting DIY hand fans. Photos by Anna Carreras. Gamboa, Panama.

Results

Glass frog hand fan. Photo by Anna Carreras. Gamboa, Panama.

Two different models of the Froggy camouflage handheld fans were created. The green one is inspired by the glass frogs and the orange fan is inspired by the pumilio dart frog. Both frogs live in Panama.

Glass frog and Pumilio dart frog. Photos by Anna Carreras and Pavel Kirillov [CC BY-SA 2.0]. Gamboa and Bocas del Toro, Panama.
Glass frog hand fan. Photo by Anna Carreras. Gamboa, Panama
Pumilio dart frog hand fan. Photo by Pavel Kirillov [CC BY-SA 2.0] and Anna Carreras. Gamboa, Panama

The glass frog handheld fan and the pumilio dart frog handheld fan integrated quite well with Gamboa’s surroundings and the rainforest.

Glass frog hand fan. Photo by Anna Carreras. Gamboa, Panama.
Pumilio dart frog hand fan. Photo by Anna Carreras. Gamboa, Panama.
Glass frog hand fan camouflaged between leaves. Photo by Anna Carreras. Gamboa, Panama.

Conclusions and future work

To  act  upon  our  surveying  world camouflage is one of the plans we can play. It rises issues of mimesis, crypsis, perception, privacy and identity. Some artistic projects about fashion and cosmetics have been developed with this idea, like CV Dazzle and HyperFace, among others. The Froggy camouflage handheld fans project sums up in this direction creating hand fans inspired by Panama’s frogs camouflage strategies.

We can gain some knowledge and learn from animals and their hiding techniques. Some animal camouflage skin coloration can be modeled as a quite simple dynamic system that generates complex ordered patterns. We can mathematically model and code the system to simulate the growing process of frogs skin coloration. It helps us to better understand how different frog species have certain particular patterns. Moreover it gives us some insight about how order can emerge from random initial conditions.

Different animal patterns and camouflage tactics can be further investigated. It can help us to achieve different and diverse algorithms and colored results. They can suit in different environments and they can help us camouflage from the increasing number of surveillance systems. A battle between algorithms learned and borrowed from nature against vigilance algorithms.

Exhibition

Dinalab open Saturday exhibition. Photo by Anna Carreras. Gamboa, Panama.
Dinalab open Saturday exhibition. Photo by Anna Carreras. Gamboa, Panama.

Acknowledgments

First I would like to thank Dr. Andrew Quitmeyer for organizing the event and all the participants I met at Dinacon Gamboa. And thanks to Marta, Mónica, Tomás, Jorge, Päivi and Dani to help me documenting the work.

References

Book The Chemical Basis of Morphogenesis. Alan Turing. 1952.

Book Orden y Caos en Sistemas Complejos. Ricard V. Solé, Susanna C. Manrubia. 2000.

Videotutorial Coding challenge #13: Reaction Diffusion Algorithm in p5.js. Daniel Shiffman. 2016.

Project CV Dazzle: Camouflage from face detection. 2010.

Project HyperFace: False-Face Camouflage. 2017.

Audio Synthesis of the Túngara Frog Call

Before the sun had even set on my first day in Gamboa I had already heard excited chattering about the sound of the “Laser Frogs”. Once it got dark there was a seemingly ubiquitous chorus of these laser sounds, an asynchronous melange of descending glissandi. One might mistake this biophony for a retro video-game arcade, but it is in fact the revelry of an amphibious Bacchanalia.

Túngara Frog in a puddle, photo courtesy of Mangtronix
Chorus of Tungara frogs at night in Gamboa
Spectrogram of the frog chorus

First Attempt

I had other plans and project ideas before arriving at DINACON, but I found myself continuously drawn to the sound of these frogs. I was completely ignorant of them at first, having no idea what their actual name was or anything about their behavior or even what they looked like. I just really liked the way they sounded and kept listening. Indeed these frogs sound like a laser beam from a video game, and since I have worked as a sound designer and synthesized laser beam sounds for video games, I thought “I bet I can synthesize these frogs!”.

My first attempt was a very quick patch using the ES2 synthesizer in Logic Pro. I did this based entirely on listening to the frogs before analyzing the spectrogram in detail. It captured the general gesture of the descending tone, but didn’t capture the timbre or slope of the glissando very well.

ES2 Logic Pro Patch for Laser Frog Synthesis
Lazer Frog Synth attempt #1

Making the Whine

Although the first attempt was not convincing enough, it was close enough to encourage me to continue on my quest to synthesize the frogs call. I began by inspecting an isolated call from one frog via the spectrogram in Audacity.

Túngara frog recording with whine and three chucks
Spectrogram of Túngara frog recording with whine and three chucks

There are many noticeable things from this spectrogram that further inform what we hear. The first being that the frogs make not only this “laser” sound, but also have a percussive sound that follows it. At first I referred to these components as the “chirp” and “beep”, but after being clued in by some STRI researchers (thanks Amanda Savage!) I learned to use the terms “whine” and “chuck”. These are much better descriptions in my opinion.

I decided to use the SuperCollider programming language so that I had absolute control over the synthesis of this sound. The first area of focus was on creating a convincing “whine” using a bank of sine wave oscillators.

Looking at the spectrogram above we can see the “whine” portion of the call is a descending tone, starting around 1kHz and ending about an octave below. It also appears to have some harmonic overtones that decrease in intensity (up to about the 5th harmonic) Here is a recording and spectrogram of the first attempt in SuperCollider.

Túngara “whine” synthesized, first attempt in SuperCollider
Spectrogram of synthesized Túngara whine in SuperCollider

This was already sounding better, but by looking at the spectrogram of the synthetic whine some things are obviously still lacking. First, the slope of the glissando is still too linear, it needs to have more on a exponential (perhaps cubic?) curve to it. Additionally the upper harmonics are too strong and need to be attenuated relative to their ordinality. (The higher the harmonic, the less loud it is)

Making the Chuck

After a few more iterations of refining the whine, I moved onto the chuck.

Spectrogram of Túngara frog chucks.

Looking at the chucks in the above spectrogram we can see partials at relatively even spacing. We could perhaps model this by using a harmonic tone with a fundamental frequency of ~200 Hz or ~250 Hz, with the fundamental and first few overtones missing. The chucks seem to have their highest peak around 2.75 kHz. Is this sound produced via some sort of formant resonance? What mechanism makes it seemingly harmonic but with a missing fundamental? This is unclear to me, but I can recreate the sound nonetheless!

This group of three chucks have different durations, and the last one seems to have a downward pitch contour but not nearly as pronounced as the whine. The first two beeps are approximately 50 milliseconds long, and the third is 40ms.

Using the same approach as the whine, I used a bank of sine wave oscillators to recreate the chuck. Below is a recording and spectrogram along with the synthetic whine.

Synthetic whine and chuck of Túngara frog
Recording of synthetic whine and chuck of Túngara frog

While the timing of the chucks is accurate, the tone is not convincing. I continued to iterate on the implementation until settling on the one below.

SuperCollider GUI Application

For presentation at Dinalab I put together a simple GUI application which allows the user to playback a recording of an isolated Túngara call and compare it to the synthetic whine and chuck. Additionally there are knobs to alter the pitch of both the whine and chuck to hear what GIANT or tiny Túngara frog might sound like.

Video of Tungara Frog Synth SuperCollider GUI Application

Here is the audio of the final form the synthesizer took, there is still room for improvement of course.

Version 6 of Túngara frog synthesizer

Playback in the Field

In order to see if my synthesizer was effective at blending in with Túngara frogs in the field, I did some simple, not very well controlled tests on the streets of Gamboa.

Basically, I walked up to a pond where I heard Túngara frogs calling and they would usually stop calling as I approached. Then with my field recorder running I would play the synthesized call from my cell phone and wait to hear a response.

Here is the first trial (that loud percussive sound in the background is a Gladiator frog, I think) The synth is mostly in the left channel while the other frogs are mostly in the right.

Field test 1 of Túngara frog synthesizer

After shuffling around a bit, the frogs got quiet and I tried again.

Field test 2 of Túngara frog synthesizer

Now, can I conclusively say that the frogs responded to my call? I do not know, I am not a field biologist or experienced with phonotaxis studies, but the results of these simple tests seem promising. I think the frogs are buying my synthetic call.

Future Work

I really enjoyed working on this project and am very interested in improving the audio synthesis and application interface so that it is useful to researchers both in the field and the laboratory. If you study frogs, bioacoustics, phonotaxis or have interest in this project please get in touch with me, I would love more feedback.

From my perspective, the synthesis could still use some refinement. First, it could use better filtering of the whine, perhaps via a resonant filter based on accurate resonances of the frogs vocal apparatus? Additionally, more variability in chuck production would be useful. With more analysis of recordings and a bit more reading on the physiology of the chuck production I think I could better refine the synthesis.

Some final questions:

Perhaps I should port this synthesizer for use in a web/mobile app?

Maybe I could synthesize Gladiator (or other) frog calls?

What additional features would be useful?

Do you have comments, criticisms or any feedback?

Acknowledgments

First I would like to thank all the participants I met at Dinacon, and Dr. Andrew Quitmeyer for organizing the event.

Amanda Savage was very generous in talking with me about my project and in introducing me to the vast literature and research available on Túngara frogs.

References and Further Reading

Quick Guide – Túngara Frogs, Rachel A. Page and Ximena E. Bernal

The Túngara Frog: A Study in Sexual Selection and Communication, Michael J. Ryan

Complex Call Production in the Túngara Frog, M. Gridi-Papp

Unlucky túngaras

There are many, many more papers written about these frogs. They are certainly one of the most studied frogs in documented human history.

-Phillip Hermans
Very Good Listening

www.verygoodlistening.com