Rhythmically repeated patterns of pulsed vocalizations in wild narwhals (Monodon monoceros)

Sequences of vocalizations are indicative of communicative complexity. However, relative to birds and terrestrial mammals, the extent to which marine mammals use vocal sequences is not well understood. I provide the first investigation into vocal sequences in narwhals (Monodon monoceros), a gregarious Arctic cetacean. Eight female narwhals were fitted with animal-borne recording devices, resulting in one of the largest datasets of narwhal acoustic behaviour to date. I used a combination of visual and quantitative classification procedures to rigorously demonstrate stereotyped organizational properties of subjectively defined sequence types. Next, acoustic characteristics were used to generate coarse inferences regarding patterns of sequence use across individuals. Finally, I used generalized linear models (GLMs) to assess the behavioural and acoustic contexts under which sequences were produced. I identified two types of sequences: “paired” patterns, consisting of combinations of two stereotyped click-based calls, the pair of which were often repeated in rapid succession. While these calls were rare, I found multiple subtypes that were predominantly associated with recordings from specific tags. I secondly identified “burst pulse series”, temporally stereotyped sets of short burst-pulses which themselves were combined into repetitive vocalization events. I found few links between sequence use and behaviour, though burst-pulse series were more likely to be produced in periods when other vocalizations were heard, suggesting possible use in social contexts. These findings extend the set of odontocetes which are known to use sequences of vocalizations. Both sequence types show rhythmic repetition of lower-level patterns, suggestive of hierarchical organizational principles. Furthermore, paired patterns constitute the first evidence of multi-unit sequences in the family Monodontidae. I propose that further inquiry into vocal sequences in narwhals and other understudied marine mammals is warranted

Cross-modal perception of identity by sound and taste in bottlenose dolphins

Funding: The study was supported by a Marie Skłodowska-Curie fellowship of the European Commission, grant number 661214 (J.N.B. and V.M.J.)While studies have demonstrated concept formation in animals, only humans are known to label concepts to use them in mental simulations or predictions. To investigate whether other animals use labels comparably, we studied cross-modal, individual recognition in bottlenose dolphins (Tursiops truncatus) that use signature whistles as labels for conspecifics in their own communication. First, we tested whether dolphins could use gustatory stimuli and found that they could distinguish between water and urine samples, as well as between urine from familiar and unfamiliar individuals. Then, we paired playbacks of signature whistles of known animals with urine samples from either the same dolphin or a different, familiar animal. Dolphins investigated the presentation area longer when the acoustic and gustatory sample matched than when they mismatched. This demonstrates that dolphins recognize other individuals by gustation alone and can integrate information from acoustic and taste inputs indicating a modality independent, labeled concept for known conspecifics.Publisher PDFPeer reviewe

Vocal sequences in narwhals (Monodon monoceros)

Sequences are indicative of signal complexity in vocal communication. While vocal sequences are well-described in birds and terrestrial mammals, the extent to which marine mammals use them is less well understood. This study documents the first known examples of sequence use in the narwhal (Monodon monoceros), a gregarious Arctic cetacean. Eight female narwhals were fitted with animal-borne recording devices, resulting in one of the largest datasets of narwhal acoustic behaviour to date. A combination of visual and quantitative classification procedures was used to test whether subjectively defined vocalization patterns were organized into sequences. Next, acoustic characteristics were analyzed to assess whether sequences could disclose group or individual identity. Finally, generalized linear models was used to investigate the behavioural context under which sequences were produced. Two types of sequences, consisting of “paired” patterns and “burst pulse series,” were identified. Sequences of burst pulse series were typically produced in periods of high vocal activity, whereas the opposite was true for sequences of paired patterns, suggesting different functions for each. These findings extend the set of odontocetes which are known to use vocal sequences. Inquiry into vocal sequences in other understudied marine mammals may provide further insights into the evolution of vocal communication.Publisher PDFPeer reviewe

Cross-modal perception of identity by sound and taste in bottlenose dolphins

While studies have demonstrated concept formation in animals, only humans are known to label concepts to use them in mental simulations or predictions. To investigate whether other animals use labels comparably, we studied cross-modal, individual recognition in bottlenose dolphins (Tursiops truncatus) that use signature whistles as labels for conspecifics in their own communication. First, we tested whether dolphins could use gustatory stimuli and found that they could distinguish between water and urine samples, as well as between urine from familiar and unfamiliar individuals. Then, we paired playbacks of signature whistles of known animals with urine samples from either the same dolphin or a different, familiar animal. Dolphins investigated the presentation area longer when the acoustic and gustatory sample matched than when they mismatched. This demonstrates that dolphins recognize other individuals by gustation alone and can integrate information from acoustic and taste inputs indicating a modality independent, labeled concept for known conspecifics

Species information in whistle frequency modulation patterns of common dolphins

Funding for this project was generously provided by the Office of Naval Research Marine Mammals and Biology program.The most flexible communication systems are those of open-ended vocal learners that can acquire new signals throughout their lifetimes. While acoustic signals carry information in general voice features that affect all of an individual's vocalizations, vocal learners can also introduce novel call types to their repertoires. Delphinids are known for using such learned call types in individual recognition, but their role in other contexts is less clear. We investigated the whistles of two closely related, sympatric common dolphin species, Delphinus delphis and Delphinus bairdii, to evaluate species differences in whistle contours. Acoustic recordings of single-species groups were obtained from the Southern California Bight. We used an unsupervised neural network to categorize whistles and compared the resulting whistle types between species. Of the whistle types recorded in more than one encounter, 169 were shared between species and 60 were species-specific (32 D. delphis types, 28 D. bairdii types). Delphinus delphis used 15 whistle types with an oscillatory frequency contour while only one such type was found in D. bairdii. Given the role of vocal learning in delphinid vocalizations, we argue that these differences in whistle production are probably culturally driven and could help facilitate species recognition between Delphinus species.Publisher PDFPeer reviewe

Repeated downsweep vocalizations of the Araguaian river dolphin, Inia araguaiaensis

Funding was provided by the Swarosvki Foundation and World Wide Fund for Nature Brazil.Araguaian botos (Inia araguaiaensis) are known to produce pulsed as well as tonal sounds. This study documents the first evidence for repetitive sequences of downsweep whistles in botos that appear to be shared between individuals, and the context of their occurrence is investigated. Boat surveys were conducted along the Tocantins River located in the Eastern Amazon over a period of 42 days between 2012 and 2018. Eighty-two groups of Araguaian botos were observed, and 43 h of sound recordings were acquired. 632 downsweep whistles were recorded in 10 encounters. Four of these encounters contained downsweep bouts (21 bouts with ≥2 whistles) with short inter-call intervals (bout criterion 50 s) and up to 161 whistles. A statistical relationship was not found between downsweep occurrence and any of the contextual parameters that were investigated, including socializing, travelling, feeding, group size, presence of calves, and socio-sexual displays. The rarity of these signals makes them unlikely candidates for individual or group identification. It is more likely that they are associated with very specific contexts, such as nursing or mating, both of which were rarely observed in this study. Further studies are required to investigate context specificity and elucidate the function of these signals.PostprintPeer reviewe

Dolphin communication during widespread systematic noise reduction-a natural experiment amid COVID-19 lockdowns

Underwater noise from human activities is recognized as a world-wide problem, with important repercussions on the acoustic communication of aquatic mammals. During the COVID-19 pandemic, the government of Panama went into a nationwide lockdown to limit the spread of the virus. This lockdown resulted in the closing of tourism infrastructure and limited mobility in both land and coastal areas. We used this “natural experiment” as an opportunity to study the impact of tour-boat activities on dolphin communication by using passive acoustic monitoring data collected before and during the lockdown at Dolphin Bay, Bocas del Toro, Panama. During the lockdown, tour-boat activity was absent, but boats transporting people and supplies were allowed to circulate. The shift in type of boat activity within the lockdown resulted in lower ambient noise levels and more frequent detections of dolphin sounds. We also detected a more diverse whistle repertoire during the lockdown than in the pre-lockdown period, even when accounting for variation in sample coverage. A Random Forest Analysis classified whistles between the two periods with high accuracy (92.4% accuracy, κ = 0.85) based primarily on whistle modulation and duration. During the lockdown, whistles were longer in duration and less modulated than pre-lockdown. Our study shows that a shift in boat traffic activity can generate significant changes in dolphin habitat, and in their communicative signals, an important consideration given ongoing unregulated ecotourism in the region

Making the case for Temporary Migrant Worker Programmes: Evidence from the UK's rural guestworker (‘SAWS’) scheme

The UK has had a Temporary Migrant Worker Programme (TMWP) for agricultural ‘guestworkers’ since 1943. Most recently referred to as the Seasonal Agricultural Workers Scheme (SAWS), SAWS accommodated 25,000 workers per annum by its 2004 peak. However, the UK government then announced the scheme’s closure (initially for 2011, but then delayed until 2014). This paper examines employers’ response to this closure and, specifically, juxtaposes the academic critiques of TMWPs with the very strong employer preference for them. This preference, the paper concludes, is about the way in which TMWPs allow labour to be more readily and more extensively controlled, and, also allow employers access to ‘better quality’ workers. Considering these benefits of quality and control, alongside the academic critiques, the paper concludes that SAWS should be retained, but with major changes