# Bottlenose Dolphins' Clicks Comply with Three Laws of Efficient Communication
## 1 Introduction
Social Structure: Animals with complex social structures, like dolphins and primates, benefit from efficient communication to maintain social bonds, coordinate group activities, and navigate social hierarchies. 3. Cognitive Abilities: Species with higher cognitive abilities are more likely to develop sophisticated communication systems that follow linguistic laws. This includes the ability to learn, remember, and produce a wide range of sound vocalisations. 4. Environmental Factors: The habitat and environmental conditions can influence the development of communication systems. For example, animals in dense forests may develop shorter, more frequent calls to avoid sound attenuation, while those in open environments may use longer calls. * Phylogenetic Constraints: Some species may have inherent biological limitations that prevent the development of complex vocal systems. These constraints can be anatomical, neurological, or related to the species' evolutionary history. * Functional Needs: The specific needs of a species, such as hunting, mating, or territory defence, can shape their communication systems. Species that rely on vocalisations for these critical functions are more likely to develop efficient and structured communication. In this regard, [PERSON] [15] studied sixteen whale and dolphin species and found that only for eleven of these does the structure of communication align well with [PERSON]'s law and [PERSON]'s law of abbreviation, similarly to human speech. Dolphins produce three primary types of acoustic signals: frequency-modulated whistles for social communication, echolocation clicks for navigation and hunting and burst-pulsed sounds for social interactions [20]. Among these, whistles and clicks are the most extensively studied in bottlen dolphins (_Tursiops truncatus_) [20]. Whistles occur within the human audible range and are closely associated with intraspecies communication [22]. A controlled study has shown that their distribution conforms to [PERSON]'s frequency-rank law [23]. Notably, bottlen dolphins produce individually distinctive signature whistles that function analogously to names, facilitating individual recognition and maintaining group cohesion [24; 25]. These signature whistles are learned early in life and remain stable over time, serving as a key component of their social communication system. Clicks, in contrast, are brief broadband pulses generated by phonic lips located beneath the blowhole. The sound is focused through the lipid-rich melon into a narrow, directional beam projected into the water [26; 27; 28]. These echolocation clicks typically last 40 to 150 microseconds and span a frequency range of approximately 20 to 150 kHz--well beyond human auditory capabilities [29; 30]. They can be emitted as isolated pulses or in sequences known as click trains. Studies on dolphin clicks highlighted the complexity and adaptability of dolphin echolocation, providing insights into their sonar system and communication abilities [19; 20; 21]. The role of clicks in echolocation is well documented [31; 32; 33; 34]. Additionally, emerging research suggests that click sequences may also serve communicative functions among conspecifics at varying distances [11; 12], although this remains to be confirmed by controlled studies. In the realm of dolphin cognition research, various studies [35; 36; 37; 38; 39; 40; 41] used clustering techniques to categorise whistles produced by adult and infant bottlenose dolphins into discrete types. Subsequently, they analysed their distributions concerning [PERSON]'s rank-frequency law. According to these studies, this distribution manifests a linear dependency on a log-log scale with a slope varying from about \(-0.82\) for newborns to up to \(-1.07\) within 2-8 months and converging on the adult value of about \(-0.95\) afterwards. This indicates that dolphins' use of whistles is broadly in line with the predictions of [PERSON]'s law and the functional tension hypothesis [1].