Evidence for vocal learning in juvenile male killer whales, Orcinus orca, from an adventitious cross-socializing experiment

Multimodal imitative learning and synchrony in cetaceans: A model for speech and singing evolution

Multimodal imitation of actions, gestures and vocal production is a hallmark of the evolution of human communication, as both, vocal learning and visual-gestural imitation, were crucial factors that facilitated the evolution of speech and singing. Comparative evidence has revealed that humans are an odd case in this respect, as the case for multimodal imitation is barely documented in non-human animals. While there is evidence of vocal learning in birds and in mammals like bats, elephants and marine mammals, evidence in both domains, vocal and gestural, exists for two Psittacine birds (budgerigars and grey parrots) and cetaceans only. Moreover, it draws attention to the apparent absence of vocal imitation (with just a few cases reported for vocal fold control in an orangutan and a gorilla and a prolonged development of vocal plasticity in marmosets) and even for imitation of intransitive actions (not object related) in monkeys and apes in the wild. Even after training, the evidence for productive or "true imitation" (copy of a novel behavior, i.e., not pre-existent in the observer's behavioral repertoire) in both domains is scarce. Here we review the evidence of multimodal imitation in cetaceans, one of the few living mammalian species that have been reported to display multimodal imitative learning besides humans, and their role in sociality, communication and group cultures. We propose that cetacean multimodal imitation was acquired in parallel with the evolution and development of behavioral synchrony and multimodal organization of sensorimotor information, supporting volitional motor control of their vocal system and audio-echoic-visual voices, body posture and movement integration.

Vocal production learning in mammals revisited

Vocal production learning, the ability to modify the structure of vocalizations as a result of hearing those of others, has been studied extensively in birds but less attention has been given to its occurrence in mammals. We summarize the available evidence for vocal learning in mammals from the last 25 years, updating earlier reviews on the subject. The clearest evidence comes from cetaceans, pinnipeds, elephants and bats where species have been found to copy artificial or human language sounds, or match acoustic models of different sound types. Vocal convergence, in which parameter adjustments within one sound type result in similarities between individuals, occurs in a wider range of mammalian orders with additional evidence from primates, mole-rats, goats and mice. Currently, the underlying mechanisms for convergence are unclear with vocal production learning but also usage learning or matching physiological states being possible explanations. For experimental studies, we highlight the importance of quantitative comparisons of seemingly learned sounds with vocal repertoires before learning started or with species repertoires to confirm novelty. Further studies on the mammalian orders presented here as well as others are needed to explore learning skills and limitations in greater detail. This article is part of the theme issue 'Vocal learning in animals and humans'.

Allopatric humpback whales of differing generations share call types between foraging and wintering grounds

Humpback whales (Megaptera novaeangliae) are a cosmopolitan baleen whale species with geographically isolated lineages. Despite last sharing an ancestor ~ 2-3 million years ago, Atlantic and Pacific foraging populations share five call types. Whether these call types are also shared between allopatric breeding and foraging populations is unclear, but would provide further evidence that some call types are ubiquitous and fixed. We investigated whether these five call types were present on a contemporary foraging ground (Newfoundland, 2015-2016) and a historic breeding ground (Hawaii, 1981-1982). Calls were classified using aural/visual (AV) characteristics; 16 relevant acoustic variables were measured and a Principal Component Analysis (PCA) was used to examine within-call and between-population variation. To assess whether between-population variation influenced classification, all 16 variables were included in classification and regression tree (CART) and random forest analyses (RF). All five call types were identified in both populations. Between-population variation in combined acoustic variables (PC1, PC2, PC3) was lower within call types than among call types, and high agreement between AV and quantitative classification (CART: 83% agreement; RF: 77% agreement) suggested that acoustic characteristics were more similar within than among call types. Findings indicate that these five call types are shared across allopatric populations, generations, and behavioural contexts.

Bias and Misrepresentation of Science Undermines Productive Discourse on Animal Welfare Policy: A Case Study

Simple Summary

Creating good animal welfare-related laws, regulations, and policies depends on accurate knowledge. To that end, scientific reviews that explain and contextualize the relevant research can be powerful tools for informing decision-makers, assuming these reviews represent the state of the scientific knowledge accurately and objectively. In this commentary, we examine the major flaws, biases, and misrepresentations of the scientific literature in one such recent review regarding the welfare and care of captive killer whales. Such pervasive problems, in this or any review, make it impossible to determine the true state of knowledge of the relevant issues, and can ultimately result in misinformed, arbitrary, or even harmful decisions about animals and their care.

Abstract

Reliable scientific knowledge is crucial for informing legislative, regulatory, and policy decisions in a variety of areas. To that end, scientific reviews of topical issues can be invaluable tools for informing productive discourse and decision-making, assuming these reviews represent the target body of scientific knowledge as completely, accurately, and objectively as possible. Unfortunately, not all reviews live up to this standard. As a case in point, Marino et al.’s review regarding the welfare of killer whales in captivity contains methodological flaws and misrepresentations of the scientific literature, including problematic referencing, overinterpretation of the data, misleading word choice, and biased argumentation. These errors and misrepresentations undermine the authors’ conclusions and make it impossible to determine the true state of knowledge of the relevant issues. To achieve the goal of properly informing public discourse and policy on this and other issues, it is imperative that scientists and science communicators strive for higher standards of analysis, argumentation, and objectivity, in order to clearly communicate what is known, what is not known, what conclusions are supported by the data, and where we are lacking the data necessary to draw reliable conclusions.

Colonizing the Wild West: Low Diversity of Complete Mitochondrial Genomes in Western North Pacific Killer Whales Suggests a Founder Effect

In the North Pacific, fish-eating R-type "resident" and mammal-eating T-type "transient" killer whales do not interbreed and differ in ecology and behavior. Full-length mitochondrial genomes (about 16.4 kbp) were sequenced and assembled for 12 R-type and 14 T-type killer whale samples from different areas of the western North Pacific. All R-type individuals had the same haplotype, previously described for R-type killer whales from both eastern and western North Pacific. However, haplotype diversity of R-type killer whales was much lower in the western North Pacific than in the Aleutian Islands and the eastern North Pacific. T-type whales had 3 different haplotypes, including one previously undescribed. Haplotype diversity of T-type killer whales in the Okhotsk Sea was also much lower than in the Aleutian Islands and the eastern North Pacific. The highest haplotype diversity for both R- and T-type killer whales was observed in the Aleutian Islands. We discuss how the environmental conditions during the last glacial period might have shaped the history of killer whale populations in the North Pacific. Our results suggest the recent colonization or re-colonization of the western North Pacific by small groups of killer whales originating from the central or eastern North Pacific, possibly due to favorable environmental changes after the Last Glacial Maximum.

SERUM COBALAMIN AND FOLATE CONCENTRATIONS AS INDICATORS OF GASTROINTESTINAL DISEASE IN KILLER WHALES ( ORCINUS ORCA)

Cobalamin and folate are water-soluble vitamins that are useful indicators of chronic gastrointestinal (GI) function in humans and some animal species. Serum cobalamin and folate concentrations in an ex situ population of killer whales ( Orcinus orca) were measured and factors that may affect their serum concentrations were identified. Serum samples ( n = 104) were analyzed from killer whales ( n = 10) both while clinically healthy and during periods of clinical GI disease as defined by clinical signs and fecal cytology. To characterize serum cobalamin and folate concentrations in clinically healthy animals, a mixed-model regression was used, with cobalamin and folate both significantly affected by weight (cobalamin: P < 0.0001, folate: P = 0.006) and season (cobalamin: P < 0.0001, folate: P < 0.0001). The marginal mean concentrations for cobalamin and folate across weight and season were 742 ± 53.6 ng/L and 30.2 ± 2.6 μg/L, respectively. The predicted 95% confidence intervals (CI) for these analytes were then compared with samples collected during periods of GI disease. Across individuals, 22% (2/9) of the folate and 80% (8/10) of the cobalamin samples from the animals with GI disease fell outside the 95% CI for the population. When comparing samples within an individual, a similar pattern presented, with 100% of cobalamin of the observed abnormal samples reduced compared to healthy animal concentration variability. The same was not true for folate. These results suggest that serum concentrations of cobalamin and folate may be useful minimally invasive markers to identify GI disease in killer whales, especially when values are compared within an individual.

Imitation of novel conspecific and human speech sounds in the killer whale (Orcinus orca)

Vocal imitation is a hallmark of human spoken language, which, along with other advanced cognitive skills, has fuelled the evolution of human culture. Comparative evidence has revealed that although the ability to copy sounds from conspecifics is mostly uniquely human among primates, a few distantly related taxa of birds and mammals have also independently evolved this capacity. Remarkably, field observations of killer whales have documented the existence of group-differentiated vocal dialects that are often referred to as traditions or cultures and are hypothesized to be acquired non-genetically. Here we use a do-as-I-do paradigm to study the abilities of a killer whale to imitate novel sounds uttered by conspecific (vocal imitative learning) and human models (vocal mimicry). We found that the subject made recognizable copies of all familiar and novel conspecific and human sounds tested and did so relatively quickly (most during the first 10 trials and three in the first attempt). Our results lend support to the hypothesis that the vocal variants observed in natural populations of this species can be socially learned by imitation. The capacity for vocal imitation shown in this study may scaffold the natural vocal traditions of killer whales in the wild.

Killer whale (Orcinus orca) behavioral audiograms

Killer whales (Orcinus orca) are one of the most cosmopolitan marine mammal species with potential widespread exposure to anthropogenic noise impacts. Previous audiometric data on this species were from two adult females [Szymanski, Bain, Kiehl, Pennington, Wong, and Henry (1999). J. Acoust. Soc. Am. 108, 1322-1326] and one sub-adult male [Hall and Johnson (1972). J. Acoust. Soc. Am. 51, 515-517] with apparent high-frequency hearing loss. All three killer whales had best sensitivity between 15 and 20 kHz, with thresholds lower than any odontocete tested to date, suggesting this species might be particularly sensitive to acoustic disturbance. The current study reports the behavioral audiograms of eight killer whales at two different facilities. Hearing sensitivity was measured from 100 Hz to 160 kHz in killer whales ranging in age from 12 to 52 year. Previously measured low thresholds at 20 kHz were not replicated in any individual. Hearing in the killer whales was generally similar to other delphinids, with lowest threshold (49 dB re 1 μPa) at approximately 34 kHz, good hearing (i.e., within 20 dB of best sensitivity) from 5 to 81 kHz, and low- and high-frequency hearing cutoffs (>100 dB re μPa) of 600 Hz and 114 kHz, respectively.

Acoustic differentiation of Shiho- and Naisa-type short-finned pilot whales in the Pacific Ocean

Divergence in acoustic signals used by different populations of marine mammals can be caused by a variety of environmental, hereditary, or social factors, and can indicate isolation between those populations. Two types of genetically and morphologically distinct short-finned pilot whales, called the Naisa- and Shiho-types when first described off Japan, have been identified in the Pacific Ocean. Acoustic differentiation between these types would support their designation as sub-species or species, and improve the understanding of their distribution in areas where genetic samples are difficult to obtain. Calls from two regions representing the two types were analyzed using 24 recordings from Hawai'i (Naisa-type) and 12 recordings from the eastern Pacific Ocean (Shiho-type). Calls from the two types were significantly differentiated in median start frequency, frequency range, and duration, and were significantly differentiated in the cumulative distribution of start frequency, frequency range, and duration. Gaussian mixture models were used to classify calls from the two different regions with 74% accuracy, which was significantly greater than chance. The results of these analyses indicate that the two types are acoustically distinct, which supports the hypothesis that the two types may be separate sub-species.

Social complexity and cultural transmission of dialects in killer whales

Many social animals have cultural traditions that may shape their societies while the social structure can in turn influence how the culture is acquired. Killer whales possess culturally transmitted dialects. The divergence of dialects was thought to occur simultaneously and consistently with the gradual fission of matrilines. In this paper we compare the social associations across matrilineal units, Bayesian phylogeny of dialects and similarity of particular syllables to test whether dialects affect social structure and whether associations or common origin define similarity of call types. We found that neither phylogeny of dialects nor similarity of syllables was correlated to associations between matrilineal units, but similarity of syllables was correlated to phylogeny of dialects for four of the six syllables analysed. The complexity and fluidity of social ties between matrilineal units and the variation in cultural transmission patterns produce a complex relationship between the social network and the socially learned vocalizations.

Physical constraints of cultural evolution of dialects in killer whales

Odontocete sounds are produced by two pairs of phonic lips situated in soft nares below the blowhole; the right pair is larger and is more likely to produce clicks, while the left pair is more likely to produce whistles. This has important implications for the cultural evolution of delphinid sounds: the greater the physical constraints, the greater the probability of random convergence. In this paper the authors examine the call structure of eight killer whale populations to identify structural constraints and to determine if they are consistent among all populations. Constraints were especially pronounced in two-voiced calls. In the calls of all eight populations, the lower component of two-voiced (biphonic) calls was typically centered below 4 kHz, while the upper component was typically above that value. The lower component of two-voiced calls had a narrower frequency range than single-voiced calls in all populations. This may be because some single-voiced calls are homologous to the lower component, while others are homologous to the higher component of two-voiced calls. Physical constraints on the call structure reduce the possible variation and increase the probability of random convergence, producing similar calls in different populations.

Comparisons of life-history parameters between free-ranging and captive killer whale (Orcinus orca) populations for application toward species management

Data collected on life-history parameters of known-age animals from the northern (NR) and southern resident (SR) killer whales (Orcinus orca) of the eastern North Pacific were compared with life-history traits of killer whales located at SeaWorld (SEA) facilities. For captive-born SEA animals, mean age and body length at 1st estrus was 7.5 years and 483.7cm, respectively. Estimated mean age at 1st conception was different (P < 0.001) for the combined data from both northern and southern resident (NSR) free-ranging populations (12.1 years) compared to SEA (9.8 years), as was the estimated mean age at 1st observed calf (SEA: 11.1 years, NSR: 14.2 years, P < 0.001). Average calf survival rate to 2 years of age for SEA animals (0.966) was significantly greater (P = 0.04) than that for SR (0.799). Annual survival rate (ASR) for SEA increased over approximately 15-year increments with rates in the most recent period (2000-2015 ASR: 0.976) improved (P < 0.05) over the first 2 periods of captivity (1965-1985: 0.906; 1985-2000: 0.941). The SR (0.966) and NR ASR (0.977) were higher (P ≤ 0.05) than that of SEA until 2000, after which there were no inter-population differences. Based on ASR, median and average life expectancy were 28.8 and 41.6 years (SEA: 2000-2015), 20.1 and 29.0 years (SR), and 29.3 and 42.3 years (NR), respectively. The ASR for animals born at SEA (0.979) was higher (P = 0.02) than that of wild-caught SEA animals (0.944) with a median and average life expectancy of 33.1 and 47.7 years, respectively. These data present evidence for similar life-history parameters of free-ranging and captive killer whale populations and the reproductive potential and survivorship patterns established herein have application for use in future research concerning the overall health of both populations.

An agent-based model of dialect evolution in killer whales

The killer whale is one of the few animal species with vocal dialects that arise from socially learned group-specific call repertoires. We describe a new agent-based model of killer whale populations and test a set of vocal-learning rules to assess which mechanisms may lead to the formation of dialect groupings observed in the wild. We tested a null model with genetic transmission and no learning, and ten models with learning rules that differ by template source (mother or matriline), variation type (random errors or innovations) and type of call change (no divergence from kin vs. divergence from kin). The null model without vocal learning did not produce the pattern of group-specific call repertoires we observe in nature. Learning from either mother alone or the entire matriline with calls changing by random errors produced a graded distribution of the call phenotype, without the discrete call types observed in nature. Introducing occasional innovation or random error proportional to matriline variance yielded more or less discrete and stable call types. A tendency to diverge from the calls of related matrilines provided fast divergence of loose call clusters. A pattern resembling the dialect diversity observed in the wild arose only when rules were applied in combinations and similar outputs could arise from different learning rules and their combinations. Our results emphasize the lack of information on quantitative features of wild killer whale dialects and reveal a set of testable questions that can draw insights into the cultural evolution of killer whale dialects.

Disproportionate emission of bubble streams with killer whale biphonic calls: perspectives on production and function

Stereotyped pulsed calls were attributed to 11 killer whales (Orcinus orca) with and without synchronous bubble streams in three datasets collected from two facilities from 1993 to 2012. Calls with and without synchronous bubble streams and divergent overlapping high frequency components ("biphonic" vs "monophonic") were compared. Subjects produced bubbles significantly more often when calls had divergent high frequency components. However, acoustic features in one biphonic call shared by five subjects provided little evidence for an acoustic effect of synchronous bubble flow. Disproportionate bubbling supported other evidence that biphonic calls form a distinct category, but suggested a function in short-range communication.

Cultural evolution of killer whale calls: background, mechanisms and consequences

Cultural evolution is a powerful process shaping behavioural phenotypes of many species including our own. Killer whales are one of the species with relatively well-studied vocal culture. Pods have distinct dialects comprising a mix of unique and shared call types; calves adopt the call repertoire of their matriline through social learning. We review different aspects of killer whale acoustic communication to provide insights into the cultural transmission and gene-culture co-evolution processes that produce the extreme diversity of group and population repertoires. We argue that the cultural evolution of killer whale calls is not a random process driven by steady error accumulation alone: temporal change occurs at different speeds in different components of killer whale repertoires, and constraints in call structure and horizontal transmission often degrade the phylogenetic signal. We discuss the implications from bird song and human linguistic studies, and propose several hypotheses of killer whale dialect evolution.

Animal vocal sequences: not the Markov chains we thought they were

Many animals produce vocal sequences that appear complex. Most researchers assume that these sequences are well characterized as Markov chains (i.e. that the probability of a particular vocal element can be calculated from the history of only a finite number of preceding elements). However, this assumption has never been explicitly tested. Furthermore, it is unclear how language could evolve in a single step from a Markovian origin, as is frequently assumed, as no intermediate forms have been found between animal communication and human language. Here, we assess whether animal taxa produce vocal sequences that are better described by Markov chains, or by non-Markovian dynamics such as the 'renewal process' (RP), characterized by a strong tendency to repeat elements. We examined vocal sequences of seven taxa: Bengalese finches Lonchura striata domestica, Carolina chickadees Poecile carolinensis, free-tailed bats Tadarida brasiliensis, rock hyraxes Procavia capensis, pilot whales Globicephala macrorhynchus, killer whales Orcinus orca and orangutans Pongo spp. The vocal systems of most of these species are more consistent with a non-Markovian RP than with the Markovian models traditionally assumed. Our data suggest that non-Markovian vocal sequences may be more common than Markov sequences, which must be taken into account when evaluating alternative hypotheses for the evolution of signalling complexity, and perhaps human language origins.

Differences in acoustic features of vocalizations produced by killer whales cross-socialized with bottlenose dolphins

Limited previous evidence suggests that killer whales (Orcinus orca) are capable of vocal production learning. However, vocal contextual learning has not been studied, nor the factors promoting learning. Vocalizations were collected from three killer whales with a history of exposure to bottlenose dolphins (Tursiops truncatus) and compared with data from seven killer whales held with conspecifics and nine bottlenose dolphins. The three whales' repertoires were distinguishable by a higher proportion of click trains and whistles. Time-domain features of click trains were intermediate between those of whales held with conspecifics and dolphins. These differences provided evidence for contextual learning. One killer whale spontaneously learned to produce artificial chirps taught to dolphins; acoustic features fell within the range of inter-individual differences among the dolphins. This whale also produced whistles similar to a stereotyped whistle produced by one dolphin. Thus, results provide further support for vocal production learning and show that killer whales are capable of contextual learning. That killer whales produce similar repertoires when associated with another species suggests substantial vocal plasticity and motivation for vocal conformity with social associates.