# Analysis of sperm whale (Physeter macrocephalus) dialogues, click by click: an ethoacoustic approach

Lara Berkenbaum, François Sarano, Toinon Flecher, Walter M.X. Zimmer, Olivier Adam, René Heuzey, Axel Preud'Homme, Hervé Glotin

► To cite this version:

Lara Berkenbaum, François Sarano, Toinon Flecher, Walter M.X. Zimmer, Olivier Adam, et al. Analysis of sperm whale (Physeter macrocephalus) dialogues, click by click: an ethoacoustic approach. One Ocean Science Congress, Jun 2025, Nice, France. hal-05281331

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# Analysis of sperm whale (*Physeter macrocephalus*) dialogues, click by click: an ethoacoustic approach

L. Berkenbaum a,b,f, F. Sarano b,f, T. Flecher a,f, W.M.X. Zimmer g, O. Adam c,d,f, R. Heuzey b,e,f, A. Preud'homme b,e,f, H. Glotin a,b,f

a) Univ. de Toulon, Aix Marseille Univ, CNRS, LIS, DYNI team, Marseille, France b) Longitude 181, Valence, France c) Sorbonne Univ., CNRS, Inst. d'Alembert, Paris, France, d) Univ. Paris-Saclay, CNRS, Inst. des Neurosciences Paris-Saclay, Gif/Yvette, France e) Indian Ocean Marine Life Foundation, Mauritius f) CIAN, Centre Int. d'IA en Acoustique Naturelle, Toulon, France, https://cian.univ-tln.fr, g) NATO STO-CMRE, La Spezia, Italy.

lara.berkenbaum@lis-lab.fr, saranofrancois@gmail.com, olivier.adam@sorbonne-universite.fr, glotin@univ-tln.fr

## Introduction & Objective

Sperm whales (Pm) communicate using clicks. Understanding their social exchanges requires assigning each click to its emitter. However, overlapping emissions among similarly sized individuals near the surface make this attributions challenging. **How can each click be reliably assigned despite overlapping click trains ?**

<figure><img src="image_3.png" /></figure>

We developed a method for individual click train identification using a mobile acoustic array coupled with audio-video recordings, to analyse an undocumented socio-acoustic interaction between two juvenile males of the same age.

## Study context & Materials

* **Program:** "La Voix Des Cachalots" (Longitude 181) [2,3,4]. Opportunistic passive underwater observations off Mauritius.

* **Tool:** OPALE antenna: 3 hydrophones + 2 GoPros, high-definition datasets, developed by SMIOT & DYNI [5].

* **Subjects:** Dyadic interactions between juvenile males born the same year, with repeated exchanges.

* **Social behavior observed:**
  'Vocal sparring' between juvenile male sperm whales.

<figure><img src="image_4.png" /><figcaption>Fig.1: OPALE antenna 2023</figcaption></figure>

## Method 1: Source localisation

Objective: Assign each click to the individual

<figure><img src="image_5.png" /><figcaption>Fig.2: Array of three hydrophones used to calculate click arrival times</figcaption></figure>

Steps[6]:

(1) **Signal synchronisation:** between hydrophones and video audio

(2) **Automatic click detection,** followed by **manual correction**

(3) **Time Difference of Arrival (TDoA)** calculations using cross-correlation

(4) **Azimuth and elevation angle** estimation

(5) **Projection** to the GoPro camera visual range

<figure><img src="image_6.png" /><figcaption>Fig.3: Scatter plot of elevation and azimuth angles derived from TDoA on 42 detected clicks</figcaption></figure>

## Method 2: Acoustic identification

Objective: Separate overlapping click trains emissions

<figure><img src="image_7.png" /><figcaption>(2) Click detection/alignment on waveform and Constant-Q Transform (CQT)</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>(4) Inter-click interval constraint: > 0.06 s</figcaption></figure>

<caption>Vectorisation of patches</caption>

<caption>Similarity calculation</caption>

**Features extraction:**

- Maximum amplitude

- Peak-to-peak amplitude

- Centroid frequency

- Mean dB

- dB relative to peak 1

<caption>Fig.4: Processing pipeline for dimensionality reduction and HDBSCAN clustering</caption>

## Preliminary Results

<figure><img src="image_9.png" /><figcaption>Fig.5: Audio signal waveform illustrating overlapping click trains</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Fig.6: Source locations of 7 clicks overlaid, from track 1, on a GoPro video frame. Each dot represents a click; colours indicate the six-year-old juvenile males who produced them: Ali (red) and Daren (green).</figcaption></figure>

**Example analysis:**

14 sec audio-video sequence containing 2 overlapping click trains (tracks 1 & 2, fig.5), totalling 84 clicks.

* **Method 1:** precise attribution of clicks to a visually identified individuals.

* **Method 2:** reliable separation of overlapping clicks.

**Manual post-processing:** clicks not assigned to a cluster were attributed based on ICI continuity.

**Combination of both methods:** successful individual assignment, even in complex overlapping situations.

<figure><img src="image_11.png" /><figcaption>Fig.7: Clustering of 37 clicks from track 2 using UMAP for dimensionality reduction and HDBSCAN, following global z-score normalisation.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig.8: Clustering results visualised on the waveform, with each click assigned to an individual: Ali (red), Daren (green). Blue clicks, initially unclustered, were reassigned to the green cluster based on ICI values [1].</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>Fig.9: CQT patches of nine clicks (9 ms window). Ali: red frame; Daren: green frame, based on clustering results from fig.7,8.</figcaption></figure>

## Discussion & Conclusion

The two methods developed in this study are complementary :

* **Method 1** offers high spatial accuracy but is limited by distance from the array and acoustic reflections near the surface.

* **Method 2** effectively separates overlapping click trains from two individuals but is more sensitive to noise, out-of-water emission, and less stable over long sequences.

**Audio/video cross-analysis** validates clustering results and resolves ambiguities. **ICI tracking** improves the attribution of isolated or unclustered clicks.

This study provides the first documentation of a vocal interaction between two juvenile males of the same age, with a strong social affinity.

The protocol allows **reliable individual attribution**, supporting detailed exploration of social and vocal dynamics in juvenile male Pm. Preliminary findings suggest that click trains **can be acoustically distinct**, even among individuals of the similar age.

This raises research questions:

- Do stable individual acoustic signatures exist?

- Are observed differences solely attributable to click orientation?

**Ethological perspectives:** opens up promising opportunities for studying:

- intra-clan social structure,

- individual specificity in click production,

- the potential communicative functions of certain click patterns.

## Acknowledgments

We thank Longitude 181 and Label Bleu productions. This study was conducted under the official authorization of the Mauritius Authority. We thank SMIoT, V. Gies and V. Barchasz for their help in the OPALE recorder. Fieldwork, video recording, and data analysis were granted by the NGOs, Longitude 181 and 'Un Océan de Vie'. Mauritian public authorities greatly helped the project "La Voix Des Cachalots", in particular the Mauritian Prime Minister's Office, Marine Continental Shelf Exploration and Administration (MCSEA; Dr. Réza Badal & his team), AFRC (Chief Scientific officer Mr. Satish Kadhun), the MFDC (Mr. Sachin Jootun and Miss Eliana Timol), and the Tourism Authority (TA; Miss Khoudijah Boodoo, Director). We thank Navin Boodhonee for his valuable participation in the fieldwork. H.G. received the ANR AID grants AI Chair in bioacoustics ANR-20-CHIA-0014 and ULPCochlea ANR-21-CE04-0020, for hardware and analysis, localisation of cetacean communication.

## References

[1] Baggenstoss, P.M., 2011. Separation of sperm whale click-trains for multipath rejection. *J. Acoust. Soc. Am.*, 129(6), 3598-3609.

[2] Girardet, J. and al., 2022. New Insights Into Genetic Diversity, Kin Relationships and Social Fidelity of Indian Ocean Male Sperm Whales.

[3] Sarano, V. and al., 2022. Underwater photo-identification of sperm whales off Mauritius. *Marine Biology Research*.

[4] Sarano, F. and al., 2023. La Voix des Cachalots, programme recherche Longitude181, https://www.longitude181.org

[5] Glotin, H., and al., DCLDE 2024. OPALE: a super resolution audiovisual mobile antenna for cetacean ethoacoustical researches.

[6] Zimmer, W.M.X. (2013). Range estimation of cetaceans with compact volumetric arrays. *J. Acoust. Soc. Am.*, 134(3), 2610-2618.