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Whispers of the Deep

by Laura Mittelman

art by Hailey Kopp


“Sperm whales live in an environment totally different from ours, one with completely different constraints. Where we are visual, they see the world through sound—both the sounds they hear and the sounds they make.” (Whitehead, as cited in Wagner, 2011)


Have you ever wondered what it would be like to “see” the world through sound? I bet you can’t quite imagine it because, unlike sperm whales, humans aren’t equipped with echolocation—a sophisticated biological sonar system that grants sperm whales one of the most powerful acoustic signaling devices in the animal kingdom. Far from whispers, these sound waves are incredibly powerful, producing the highest sound pressure ever measured from an animal. This allows sperm whales to navigate the deep oceans, hunt prey, and communicate by listening for their echos [1, 2].

Within the realm of animal communication research, scientists have explored the nuanced language signals of spiders, pollinators, rodents, birds, primates, and cetaceans [3]. Amidst this diversity, cetaceans—whales, dolphins, and porpoises—exhibit a unique communicative complexity, demonstrating a wide array of essential social skills that parallel many of our own social and linguistic characteristics. Toothed whales, which include sperm whales, are among the few animals that possess the capacity for vocal production learning [3]. Their unique ability to integrate and reproduce novel sounds has allowed toothed whales to develop sound communication repertoires; and, the sophistication with which whales integrate this skill into their social world distinguishes them as an exemplary species of vocal production learning.

The one-of-a-kind social intelligence of whales has captured the intrigue of scientists, who are beginning, now more than ever, to unravel the threads of their social bonds and fleeting encounters, attributing certain communicative vocalizations to a dynamic structure of inter-whale relationships. Importantly, technological advancements in research innovations have been central to recent findings in the field. The logistical difficulties associated with the natural observation of marine life, especially whales, have proven to be a historical obstacle in the development of whale communication theory [3]. But thanks to modern technology and machine learning systems, a more profound understanding of non-human communication is forthcoming [3].


Neurobiology of the Bioacoustic System

“A sperm whale is to my fancy the most uncomely shaped animal that I can think of.” (Ellsworth, 1990)

Have you ever marveled at the sight of whales gracefully navigating the ocean in pods, or considered their harmonious synchronization of movements? This captivating display is not just a random act of nature but a glimpse into the intricate social dynamics and familial structures of sperm whales. In fact, sperm whales have evolved to interact within a highly dynamic society, marked by long-lasting social relationships and frequent stranger interactions [3].

Sperm whales are born into closely bonded matrilineal families, where multiple females and their offspring travel together in a pod, making group decisions related to hunting and foraging [4, 5]. While pods are characterized by females and their young, male whales typically travel solo, breaking apart from their family pods around age five [6, 7]. Within family lineages, female sperm whales exhibit behaviors that provide a strong testament to their high-functioning sociability and commitment to family, such as collectively defending and raising their offspring [8]. For example, female whales will often nurse each others’ calves, forming bonds that evolve into decade-long relationships [8]. Individual pods also come together to form clans—groups of hundreds, even tens of thousands of whales— with shared movement patterns, such as diving synchronization, coordinated foraging, and similar diets, crucial for the clans’ survival [9]. Sperm whales exhibit diversity among these characteristics between clans, and despite overlapping ocean territory, clans remain socially segregated [3]. This resemblance of community building is remarkable for non-human species and speaks strongly to their advanced communication abilities.

To really appreciate and understand the awe-inspiring social architecture that spans the world’s oceans, we must consider the neuroscience of sperm whales, which has amassed an impressive array of neurophysiological traits through 50 million years of aquatic evolution. After all, their fascinating social behavior, cognitive prowess, and sonar capabilities are direct reflections of their sophisticated brain structure [10].

The most profound neurophysiological development in sperm whales is their echolocation capacity, which allows them to navigate, detect objects, and communicate in a three-dimensional auditory world. Sperm whales also possess advanced auditory processing skills and communicative abilities, which ultimately allow for an advanced network of inter-whale socialization [10]. This unique combination of neurobiological features shapes their complex behavior and communication systems, making sperm whales highly cultural creatures, much like ourselves. Thus, when comparing the evolutionary routes of whales and human brain development, we can see a common path toward achieving neurobiological and cognitive sophistication in two completely distinct species in widely different habitats [11]. This parallelism is what captivates the fascination of scientists, motivating them to further study and develop our understanding of whale sociocultural dynamics.

Their brain—one of the largest brains of all animals on Earth— harnesses a rich neurological capacity, bestowing on sperm whales a sophisticated intellectual and social power [12, 13]. In fact, their brain is six times heavier than a human brain, with complex

cerebral structures indicative of advanced cognition [14]. Much like our brain, which has different brain regions designated for specific functions, toothed whale brains exhibit similar segmentation. In fact, the toothed whale brain (which includes that of the sperm whale) surpasses the human brain in gyrification, the number of folds and convolutions on its surface [14]. Increased gyrification is associated with increased intelligence and cognitive ability in humans [15]. Therefore, although the brain circuitry of sperm whales differs significantly from that of humans, it is likely that their social and intellectual capacity is on a similar level to ours [14].

Zooming out to the overall head-to-body ratio of the sperm whale, their massive head—which houses not only their sophisticated brain but also their enormous nose—is a hallmark feature of sperm whales [16]. Claiming one-third of their entire body length and weight, you may be surprised to learn that their nasal complex is not designed to house a robust olfactory (smell) system [12]. Rather, their olfactory system is completely absent. In fact, the regression of the sperm whale olfactory system begins during the early fetal period of neurodevelopment, when the olfactory bulb (the main receiving center for sensory input relating to smell) and the olfactory nerve (which transmits smell information from the olfactory bulb to the brain) completely vanish [10]. However, despite the absence of smell, adult sperm whales are not left short of five senses. Echolocation, the biological sonar system used by whales to navigate, forage, and communicate via the production of sound waves and their echos, assumes the role of their fifth sense [12, 17]. Scientists have coined this phenomenon the echolocation priority hypothesis, which states that the evolutionary acquisition of echolocation in cetaceans catalyzed the reduction, or in the case of sperm whales, the complete disappearance of, the olfactory system [17, 18]. Thus, the evolution of echolocation and the sperm whale biosonar system illustrates a fascinating tradeoff, where smell was sacrificed for the advanced ability to perceive their environment through sound.

The evolution of echolocation also allowed sperm whales to meet the specific sensory demands of the deep blue. They developed the ability to locate prey, communicate, and navigate within the darkness of the mesopelagic zone: the layer of ocean ranging from 200 to 1,000 meters below the surface, where sunlight is barely detectable [19, 20]. The evolution of such a powerful biosonar system epitomizes sperm whales as “animals of extremes” and enables them to produce the most powerful sounds in the animal kingdom [3, 4, 20]. In fact, their large head serves as the origin of their biological name: Physeter macrocephalus–macrocephalus, translating to “large head” [3]. Encased within their biosonar system are various interconnected biological structures, consisting of soft organs weaved within air sacs and nasal passages, all contributing to their remarkable sense of echolocation. Interestingly, the nasal cavity of sperm whales is asymmetrical, with the left side allotted for the respiratory system, and the right specialized for sound production [21].

Focusing on the right side, we find two of the sperm whale’s most important soft organs: the ‘spermaceti’ and ‘junk’ organs. The spermaceti organ is a massive, cone-shaped structural sac in the nose filled with about 1,900 liters of oil, known as spermaceti oil—which was the once-prized oil harvested for making spermaceti candles and illuminating oils during the historical American whaling era [21, 22]. Behind the spermaceti organ, we find the frontal air sac. Together, these two structures — the spermaceti organ and the frontal air sac — work as an exceptional sound mirror within their nose [21]. At the foremost region of the spermaceti organ, a lipped structure of connective tissue forms the monkey lips, which produce sounds through a pneumatic process, much like human vocal cords [23, 24]. The second of the two organs is the junk organ, located below the spermaceti organ. Altogether, the junk and spermaceti organs, the surrounding air sacs and passageways, and the clapper system of the monkey lips make up the biosonar system, which allows for sound energy to focus into extremely powerful vocalizations [13, 21]. The sophisticated arrangement of the sperm whale’s biosonar system represents a case of remarkable evolutionary adaptation, which has enabled these gentle giants to navigate, communicate, and hunt the dark expanses of the ocean solely through echolocation.


Acoustic Communication of Sperm Whales

“...if an animal spends all morning in non-productive socializing, he must be at least twice as efficient a producer in the afternoon.” (Humphrey, 1976)

Though developed as a means to navigate the dark waters of the deep, sperm whales have adapted their bioacoustic system for complex, inter-whale communication. The sperm whale produces a distinctive brief acoustic signal that serves as the basis for all its vocalizations and is commonly referred to as a click [3]. Sometimes, but rarely, other vocalizations—squeals and trumpets—are made, but clicks serve as the primary linguistic mechanism for echolocation and communication in sperm whales [13]. Each click is constituted by a brief, highly directional, broadband soundwave, composed of an initial powerful pulse, and followed by additional pulses of decreasing ampli - tude [13]. Within the whale’s nose, the spermaceti organ and its associated structures are responsible for generating a click [25].

The intricacies of the sperm whale’s bioacoustic system have fa - cilitated their survival through the usage of clicks for navigation and hunting. Yet, across evolution, clicks have transcended their evolutionary origin to weave the complex fabric of social bondsand societal structures among sperm whales. Clicks have even been established as the foundation of sperm whales’ language system, much like the alphabets of human languages [16]. Sperm whale communication utilizes short bursts of clicks (less than 2 seconds each) as their basic language framework, string - ing multiple clicks into a stereotyped pattern recognizable by other whales. Such patterns of clicks are termed codas and are typically made up of 2-40 clicks. Codas are comparable to words used in human languages, and each clan of sperm whales may have its unique usage of these codas for communication— termed dialect—which typically contains around 20 distinct coda types. Interestingly, different sperm whale dialects have been detected in different oceans, between the Pacific, Indian, and Atlantic [16]. And, on a more local level, individual whales of a specific family share a natal dialect of approximately 10 coda types, which provides insight into potential family-spe - cific language acquisition patterns [26]. Researchers have also observed that codas appear to be rich in information about the caller’s identity [3]. This would indicate that sperm whales can recognize each other, from great distances, by their individual clicks and codas. These findings might suggest that codas contain a certain depth of meaning that contributes greatly to the formation of whale societies, paralleling the sophisticated capabilities of human linguistics [3]. Furthermore, calves ex - hibit a learning curve in language production, much like young children, producing unrecognizable coda types (“babble”) until around two years old, when they start developing a larger rep - ertoire of call types [26]. As they mature, their call repertoire narrows to the codas produced only by their natal family [26]. These ‘language’ acquisition observations parallel the brain de - velopment of young calves: their babbling reflects an immature language area in their brain, which matures as they grow, allow - ing them to gain cognitive sophistication and hone their call repertoire, much like humans.

As we look deeper into the intricate symphony of codas that sperm whales engage in, we can reveal a fascinating glimpse into their advanced language system. Sperm whales exchange codas in harmonized patterns, between two or more whales at a time [27]. Within such a ‘conversation,’ there appears to be turn-taking between each whale’s vocalizations, with response codas generated within 2 seconds of each other, sometimes overlapping and producing identical calls [27]. Remarkably, not only do these echolocation pulses travel close, within meters of nearby whales, but also travel kilometers, reaching whales far away [11, 13]. It may be wise, now, to reconsider calling these vocalizations “whispers of the deep,” as they are incredibly powerful—the most powerful sound in the animal kingdom.


From the Ocean to Understanding

“The goal is to turn data into information, and information into insight.” (Carly Fiorina, 2004) You might be wondering how researchers have started to piece together this communication puzzle, which we are just begin - ning to truly understand while studying such an elusive and inaccessible (and breathtaking) species. The schematic of the sperm whale bioacoustic data collection process paints quite a complicated picture. With multiple data sources and several techniques of data acquisition, researchers must analyze and interweave these assets towards the goal of understanding the communication of sperm whales. Outlined simply, the data acquisition process involves researchers collecting a diverse range of data: social, video, environmental, behavioral, and audio [3]. The technology used to gather these data includes (1) aerial drones, which are used to survey large areas of ocean inhabitedby sperm whales; (2) aquatic drones, also known as underwater robots and drifters, which collect audio and video recordings to analyze behavioral and communication patterns within a group of whales; (3) tethered buoy arrays, which record bioacoustic signals from several hundred meters below sea level, where sperm whales are known to hunt; and (4) tags, which are recording devices attached directly to whales [3]. Tags are the most innovative research device, providing highly detailed insight into daily behaviors and interactions between sperm whales, especially when associating activity patterns with bioacoustic recordings from tethered buoy arrays [28].

Researchers then take their observations and begin building a model to decode sperm whale communication. Let’s first consider the human language, which has a hierarchically organized phonological structure: the smallest speech unit that changes the meaning of a

word in our language is a phoneme, represented by alphabetical letters in the English language, as in reef vs. beef [29]. Our brains process phonemes according to their fundamental acoustic features in a brain area called the superior temporal gyrus (STG), also known as Wernicke’s area [30]. In the sperm whale, researchers have conjectured that codas act as the fundamental communicative unit (like a phoneme) in a similar hierarchical language structure [3]. Therefore, researchers use machine learning techniques to determine how different coda types are distinguished from one another, if features of coda clicks carry any phonotactic rules, and if sperm whales utilize formal grammatical structures when communicating [3]. These questions have yet to be fully explored and are currently the driving force behind sperm whale communication projects.

Another pressing question researchers have: do any individual coda clicks carry information or functional meaning? To answer this question, researchers are interrogating the syntax and semantics of the bioacoustic recordings they collect. Considering human language once again, we have the capacity to produce complex sentences from basic units according to linguistic rules—the syntax of our language. By applying machine learning techniques, researchers hope to form further hypotheses about the hierarchical usage of codas for inter-whale vocalization—the syntax of sperm whale communication [3].

Overall, the key question concerns the meaning behind all sperm whale vocalizations. What are these magnificent creatures saying to each other? To answer this, researchers want to identify the minimal meaning-carrying unit of whale vocalizations—the semantics of whale communication. It is already known that individual, familial, and historical information is contained within individual codas, but the majority of recorded codas remain poorly understood, as well as the inherent differences between individual clicks and coda patterns [3, 26, 31]. Nevertheless, the quest to decode the sperm whale communication system is ongoing, and everyday researchers are getting closer to unraveling the sophisticated vocalizations of these awe-inspiring mammals. Amidst this intricate exploration, we can imagine a future where sperm whale conversations rise to the surface.


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