Signature whistles in free‐ranging populations of Indo‐Pacific bottlenose dolphins,Tursiops aduncus

Common bottlenose dolphins (Tursiops truncatus) use individually distinctive signature whistles which are highly stereotyped and function as contact calls. Here we investigate whether Indo‐Pacific bottlenose dolphins (T. aduncus) use signature whistles. The frequency trace of whistle contours recorded from three genetically distinct free‐ranging populations was extracted and sorted into whistle types of similar shape using automated categorization. A signature whistle identification method based on the temporal patterns in signature whistle sequences of T. truncatus was used to identify signature whistle types (SWTs). We then compared the degree of variability in SWTs for several whistle parameters to determine which parameters are likely to encode identity information. Additional recordings from two temporarily isolated T. aduncus made during natural entrapment events in 2008 and 2009 were analyzed for the occurrence of SWTs. All populations were found to produce SWTs; 34 SWTs were identified from recordings of free‐ranging T. aduncus and one SWT was prevalent in each recording of the two temporarily isolated individuals. Of the parameters considered, mean frequency and maximum frequency were the least variable and therefore most likely to reflect identity information encoded in frequency modulation patterns. Our results suggest that signature whistles are commonly used by T. aduncus.     

Delphinid whistle production and call matching during playback of simulated military sonar

In 2007 and 2008, controlled exposure experiments were performed in the Bahamas to study behavioral responses to simulated mid‐frequency active sonar (MFA) by three groups of odontocetes: false killer whales, Pseudorca crassidens; short‐finned pilot whales, Globicephala macrorhynchus; and melon‐headed whales, Peponocephala electra. An individual in each group was tagged with a Dtag to record acoustic and movement data. During exposures, some individuals produced whistles that seemed similar to the experimental MFA stimulus. Statistical tests were thus applied to investigate whistle‐MFA similarity and the relationship between whistle production rate and MFA reception time. For the false killer whale group, overall whistle rate and production rate of the most MFA‐like whistles decreased with time since last MFA reception. Despite quite low whistle rates overall by the melon‐headed whales, statistical results indicated minor transient silencing after each signal reception. There were no apparent relationships between pilot whale whistle rates and MFA sounds within the exposure period. This variability of responses suggests that changes in whistle production in response to acoustic stimuli depend not only on species and sound source, but also on the social, behavioral, or environmental contexts of exposure.     

Whistle characteristics of common dolphins (Delphinus sp.) in the Hauraki Gulf,New Zealand

Quantifying the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographic variation, and social relevance. However, the vocalizations of free‐ranging common dolphins (Delphinus sp.) have not previously been described from New Zealand waters. We present the first quantitative analysis of whistle characteristics to be undertaken on the New Zealand population. Acoustic data were collected in the Hauraki Gulf, North Island from 28 independent dolphin group encounters. A total of 11,715 whistles were collected from 105.1 min of recordings. Seven whistle contours were identified containing 29 subtypes. Vocalizations spanned from 3.2 to 23 kHz, with most whistles occurring between 11 and 13 kHz. Whistle duration ranged from 0.01 to 4.00 s (mean ± SD; 0.27 ± 0.32). Of the 2,663 whistles analyzed, 82% have previously been identified within U.K. populations. An additional six contours, apparently unique to New Zealand Delphinus were also identified. Data presented here offer a first insight into the whistle characteristics of New Zealand Delphinus. Comparisons with previously studied populations reveal marked differences in the whistle frequency and modulation of the New Zealand population. Interpopulation differences suggest behavior and the local environment likely play a role in shaping the vocal repertoire of this species.     

Identifying signature whistles from recordings of groups of unrestrained bottlenose dolphins (Tursiops truncatus)

Bottlenose dolphins (Tursiops truncatus) have individually distinctive signature whistles. Each individual dolphin develops its own unique frequency modulation pattern and uses it to broadcast its identity. However, underwater sound localization is challenging, and researchers have had difficulties identifying signature whistles. The traditional method to identify them involved isolating individuals. In this context, the signature whistle is the most commonly produced whistle type of an animal. However, most studies on wild dolphins cannot isolate animals. We present a novel method, SIGnature IDentification (SIGID), that can identify signature whistles in recordings of groups of dolphins recorded via a single hydrophone. We found that signature whistles tend to be delivered in bouts with whistles of the same type occurring within 1–10 s of each other. Nonsignature whistles occur with longer or shorter interwhistle intervals, and this distinction can be used to identify signature whistles in a recording. We tested this method on recordings from wild and captive bottlenose dolphins and show thresholds needed to identify signature whistles reliably. SIGID will facilitate the study of signature whistle use in the wild, signature whistle diversity between different populations, and potentially allow signature whistles to be used in mark‐recapture studies.     

Automated identification and clustering of subunits within delphinid vocalizations

Tonal vocalizations or whistles produced by many species of delphinids range from simple tones to complex frequency contours. Whistle structure varies in duration, frequency, and composition between delphinid species, as well as between populations and individuals. Categorization of whistles may be improved by decomposition of complex calls into simpler subunits, much like the use of phonemes in classification of human speech. We identify a potential whistle decomposition scheme and normalization process to facilitate comparison of whistle subunits derived from tonal vocalizations of bottlenose dolphins (Tursiops truncatus), spinner dolphins (Stenella longirostris), and short‐beaked common dolphins (Delphinus delphis). Network analysis is then used to compare subunits within the vocal corpus of each species. By processing whistles through a series of steps including segmentation, normalization, and dynamic time warping, we are able to automatically cluster selected subunits by shape, regardless of differences in absolute frequency or moderate differences in duration. Using the clustered subunits, we demonstrate a preliminary species classification scheme based on rates of subunit occurrence in vocal repertoires. This provides a potential mechanism for comparing the structure of complex vocalizations within and between species.     

Characteristics of arctic ground squirrel alarm calls

Summary Arctic ground squirrels, Citellus undulatus, produce six distinctly different sounds. Each of these sounds may represent a signal in itself, but combinations of these acoustic elements or repetition of a single element produce additional signals. Several of these signals serve as alarm calls. One sound element consists of a short (0.05 sec) broad frequency chat while another is a longer (0.16 to 0.25 sec) descending narrow frequency whistle. Squirrels utter three-note chatter calls when approached by a ground predator, and a series of five or more chatters, which fade in intensity, is given upon the close approach of a ground predator as the squirrel escapes into a burrow. A single whistle, which resembles the alarm call of some birds, is given upon the approach of an aerial predator. This call is repeated at approximately six to eight second intervals if the predator alights near a squirrel and remains nearby.     

SOUND PRODUCTION AND SOUND EMISSION IN SEVEN SPECIES OF EUROPEAN TETTIGONIIDS. PART I. THE DIFFERENT PARAMETERS OF THE SONG; THEIR RELATION TO THE MORPHOLOGY OF THE BUSHCRICKET

Abstract

Comparative studies of sound production and sound emission in seven species of European tettigoniids have been carried out. The species chosen were two Tettigoniines (Tettigonia cantans, Tettigonia viridissima), two Ephippigerines (Ephippiger discoidalis, Ephippiger ephippiger), and three Decticines (Decticus albifrons, Decticus verrucivorus, Psorodonotus illyricus). The factors which determined the choice of species were the different morphology (for example body shape and weight, and wing size) of the three subfamilies. The parameters of the different songs (e.g. dominant frequency, intensity) are normally not correlated to any of the investigated morphological characteristics of the animals. In the brachypterous species intraspecific correlations exist between wing size and the dominant low frequency band of the call. This frequency band is also observable at related higher frequencies in the ultrasonic range (20–60 kHz), the observed band width increasing with frequency. Sound emission in all species is to some extent directional. This directionality is related to body size and wing structure. The song structure of the different species does not appear to be related to any observable characteristic of the habitat of die animals. A possible exception may be the song of Psorodonotus illyricus with a particularly low dominant frequency band. The phylogenetic development of the songs seems to be determined by relationships between the different species rather than to any factors contributed by the habitat.     

Differences in acoustic signals from Delphinids in the western North Atlantic and northern Gulf of Mexico

Whistle characteristics were quantitatively compared between both geographically separated and neighboring populations of Atlantic spotted dolphins (Stenella frontalis), bottlenose dolphins (Tursiops truncatus), and pilot whales (Globicephala spp.) in U.S. waters to evaluate if intraspecific acoustic differences exist between groups. We compared nine whistle characteristics between continental shelf and offshore Atlantic spotted dolphins in the western North Atlantic and between northern Gulf of Mexico and western North Atlantic bottlenose dolphins and pilot whales using discriminant analysis. Offshore Atlantic spotted dolphin whistles were significantly different (Hotelling's T², P= 0.0003) from continental shelf whistles in high frequency, bandwidth, duration, number of steps, and number of inflection points. Atlantic bottlenose dolphin whistles were significantly different (Hotelling's T², P < 0.0001) from those in the Gulf of Mexico in duration, number of steps, and number of inflection points. There was no significant difference between pilot whale whistles in the two basins. The whistle differences indicate acoustic divergence between groups in different areas that may arise from geographic isolation or habitat separation between neighboring but genetically distinct populations of dolphins. This study supports the premise that acoustic differences can be a tool to evaluate the ecological separation between marine mammal groups in field studies.     

Whistling in a noisy ocean: bottlenose dolphins adjust whistle frequencies in response to real-time ambient noise levels

Common bottlenose dolphins (Tursiops truncatus) use complex acoustic behaviours for communication, group cohesion and foraging. Ambient noise from natural and anthropogenic sources has implications for the acoustic behaviour of dolphins, and research shows that average ambient noise levels alter dolphin acoustic behaviour. However, when background noise levels are highly variable, the relationships between noise and acoustic behaviour over short time periods are likely important. This study investigates whether bottlenose dolphins altered the temporal and spectral qualities of their whistles in relation to the ambient noise present at the time the whistles were produced. Dolphin groups were recorded in Tampa Bay (western Florida) between 2008 and 2015. Six whistle parameters were analysed in spectrogram software (minimum frequency, maximum frequency, bandwidth, peak frequency, duration and number of inflection points) and ambient noise levels were calculated immediately prior to each whistle. Linear regression analysis indicated that the minimum, maximum and peak frequencies of whistles had significant positive relationships with the ambient noise levels present at the time of the whistles. These models suggested that for each 1 dB increase in ambient noise, minimum frequency increased by 121 Hz, maximum frequency increased by 108 Hz and peak frequency increased by between 122 and 144 Hz. As ambient noise is typically low frequency, this suggests that bottlenose dolphins increased whistle frequency in response to real-time noise levels to avoid masking. Future research to determine the fitness consequences of noise-induced changes in the communication behaviour of dolphins would be an important contribution to conservation efforts.     

The Kickapoo Whistle System: A Speech Surrogate

Abstract

The Mexican and Oklahoma whistle and flute languages are presented as dual surrogates which have been maintained and utilized as communications systems for over 100 years.     

Distinct patterns of geographic variation for different song components in Daurian Redstarts Phoenicurus auroreus

Capsule: Components of Daurian Redstart Phoenicurus auroreus song have evolved along independent trajectories and show a mix of clinal and dialect patterns of geographic variation.

Aims: To investigate multiple structural components of song in Daurian Redstarts Phoenicurus auroreus as they varied among five locations across South Korea. To test whether different components of the same signal can evolve along independent trajectories, or else are constrained to evolve in correlated fashion.

Methods: Two distinct song components were investigated: the introductory whistle and the complex syllable. For both segments, we made both qualitative and quantitative comparisons of similarity among individuals both within and among populations.

Results: Patterns of geographic variation differed substantially between the two song segment types. Introductory whistles varied widely both within and among individuals, and were distributed across space in a mosaic pattern. Complex syllable parts showed high within-individual similarity and a distinctly clinal pattern of geographic variation, with the exception of a distinct dialect in one population isolated by a high-elevation mountain range.

Conclusions: The results suggest that different components of Daurian Redstart songs have evolved along independent trajectories; that specific song components may show a mix of clinal and dialect patterns of geographic variation; and that different song components might simultaneously transmit distinct patterns of information about individual, dialect or species identity.     

PRELIMINARY OBSERVATIONS ON THE FISH POPULATIONS OF THE RECENTLY-IMPOUNDED KATSE RESERVOIR,LESOTHO

Summary

Katse is a new 35 km long impoundment on the Malibamatso River, a highland tributary of the Orange River in Lesotho. Two fishing surveys in 1996 yielded Barbus aeneus, Labeo capensis, Oncorhynchus mykiss and the occasional Austroglanis sclateri. Length frequency data for the first three species show modes which may represent year classes, although gillnet selectivity also plays a role. Barbus aeneus is abundant throughout the reservoir and could support a subsistence fishery. Labeo capensis is segregated by sex in the breeding season, with males remaining on the spawning grounds at the river mouths while females visit the spawning grounds for a short time to shed their eggs. The absence of small-sized Oncorhynchus mykiss in the catch may be due to pollution from mining and construction affecting the spawning grounds. The catches of larger trout and the outstanding scenery suggest that a tourist sport fishery could be developed on the reservoir based on natural recruitment supplemented, if necessary, by stocking hatchery-reared fish. As the three species are potamodromous, subsistence fishing zones will need to be clearly demarcated to prevent fishing in the vulnerable river mouth areas.     

A description of defensive hiss types in the flat horned hissing cockroach (Aeluropoda insignis)

Acoustic communication can inform studies of behaviour and phylogeny in insect species. Despite there being 4600 described species of cockroach, few studies have focused on their ability to communicate acoustically. Cockroaches have been found to produce sound in a variety of ways. Species within the tribe Gromphadorhini produce sound through modified spiracles, often referred to as hisses. Sound parameters have been described for the species Gromphadorhina portentosa and Elliptorhina chopardi. Aeluropoda insignis, within the same tribe, produces sound and is morphologically similar to these two species, but no research has been published describing its acoustic signals. Our study explores the defensive acoustic signals of this species and indicates that A. insignis is capable of producing three classes of acoustic signals (whistles, whistle–hisses and hisses) associated with defensive behaviour. Sexes differed in the entropy and the frequency of their signals, with males producing signals with lower entropy and at higher frequency than females. Future studies on acoustic communication within Blattodea could give more insight into the complexity of signals and their relationship to behavioural context.     

Communication in bottlenose dolphins: 50 years of signature whistle research

Bottlenose dolphins (Tursiops truncatus) produce individually distinctive signature whistles that broadcast the identity of the caller. Unlike voice cues that affect all calls of an animal, signature whistles are distinct whistle types carrying identity information in their frequency modulation pattern. Signature whistle development is influenced by vocal production learning. Animals use a whistle from their environment as a model, but modify it, and thus invent a novel signal. Dolphins also copy signature whistles of others, effectively addressing the whistle owner. This copying occurs at low rates and the resulting copies are recognizable as such by parameter variations in the copy. Captive dolphins can learn to associate novel whistles with objects and use these whistles to report on the presence or absence of the object. If applied to signature whistles, this ability would make the signature whistle a rare example of a learned referential signal in animals. Here, we review the history of signature whistle research, covering definitions, acoustic features, information content, contextual use, developmental aspects, and species comparisons with mammals and birds. We show how these signals stand out amongst recognition calls in animals and how they contribute to our understanding of complexity in animal communication.     

Whistle variation in Mediterranean common bottlenose dolphin: The role of geographical,anthropogenic, social,and behavioral factors

The studies on the variation of acoustic communication in different species have provided insight that genetics, geographic isolation, and adaptation to ecological and social conditions play important roles in the variability of acoustic signals. The dolphin whistles are communication signals that can vary significantly among and within populations. Although it is known that they are influenced by different environmental and social variables, the factors influencing the variation between populations have received scant attention. In the present study, we investigated the factors associated with the acoustic variability in the whistles of common bottlenose dolphin (Tursiops truncatus), inhabiting two Mediterranean areas (Sardinia and Croatia). We explored which factors, among (a) geographical isolation of populations, (b) different environments in terms of noise and boat presence, and (c) social factors (including group size, behavior, and presence of calves), were associated with whistle characteristics. We first applied a principal component analysis to reduce the number of collinear whistle frequency and temporal characteristics and then generalized linear mixed models on the first two principal components. The study revealed that both geographic distance/isolation and local environment are associated with whistle variations between localities. The prominent differences in the acoustic environments between the two areas, which contributed to the acoustic variability in the first principal component (PC1), were found. The calf's presence and foraging and social behavior were also found to be associated with dolphin whistle variation. The second principal component (PC2) was associated only with locality and group size, showing that longer and more complex tonal sound may facilitate individual recognition and cohesion in social groups. Thus, both social and behavioral context influenced significantly the structure of whistles, and they should be considered when investigating acoustic variability among distant dolphin populations to avoid confounding factors.     

MATING CALLS OF THE IBERIAN MIDWIFE TOADS ALYTES OBSTETRIC ANS BOSCAI AND ALYTES CISTERNASII

ABSTRACT

The mating calls of the Iberian midwife toads, A.o. boscai and A. cisternasii show clear differences. The calls of A.o. boscai have a shorter duration (104.8ms) and a lower fundamental frequency (1.33 kHz) than those of A. cisternasii (172.0 ms and 1.45 kHz), between 12° and 16°C. In both species signal duration was found to be influenced by temperature.     

Identification and Characteristics of Signature Whistles in Wild Bottlenose Dolphins (Tursiops truncatus) from Namibia

A signature whistle type is a learned, individually distinctive whistle type in a dolphin''s acoustic repertoire that broadcasts the identity of the whistle owner. The acquisition and use of signature whistles indicates complex cognitive functioning that requires wider investigation in wild dolphin populations. Here we identify signature whistle types from a population of approximately 100 wild common bottlenose dolphins (Tursiops truncatus) inhabiting Walvis Bay, and describe signature whistle occurrence, acoustic parameters and temporal production. A catalogue of 43 repeatedly emitted whistle types (REWTs) was generated by analysing 79 hrs of acoustic recordings. From this, 28 signature whistle types were identified using a method based on the temporal patterns in whistle sequences. A visual classification task conducted by 5 naïve judges showed high levels of agreement in classification of whistles (Fleiss-Kappa statistic, κ = 0.848, Z = 55.3, P<0.001) and supported our categorisation. Signature whistle structure remained stable over time and location, with most types (82%) recorded in 2 or more years, and 4 identified at Walvis Bay and a second field site approximately 450 km away. Whistle acoustic parameters were consistent with those of signature whistles documented in Sarasota Bay (Florida, USA). We provide evidence of possible two-voice signature whistle production by a common bottlenose dolphin. Although signature whistle types have potential use as a marker for studying individual habitat use, we only identified approximately 28% of those from the Walvis Bay population, despite considerable recording effort. We found that signature whistle type diversity was higher in larger dolphin groups and groups with calves present. This is the first study describing signature whistles in a wild free-ranging T. truncatus population inhabiting African waters and it provides a baseline on which more in depth behavioural studies can be based.     

THE ULTRASONIC SONG OF THE MOTH AMYNA NATALIS (LEPIDOPTERA: NOCTUIDAE: ACONTIINAE)

ABSTRACT

In Malaysia, males of the noctuid moth Amyna natalis were observed producing a continuous ultrasonic song of high intensity (about 102 dB SPL measured at a distance of 10 cm). The frequency spectrum of the sound impulses had its peak between 60 and 80 kHz. During song production the animals were perching on plants and moving their wings up and down quickly. Simultaneously, by twisting the wings it seems likely that a male-specific “bubble” in the forewing functions as a tymbal, resulting in sound production.     

FRESHWATER FISH OF THE ADDO ELEPHANT NATIONAL PARK

Summary

This study aimed to determine the distribution and relative abundance of freshwater fish in the Addo Elephant National Park. A total of 1578 fish specimens of 12 species were collected during surveys carried out in the Sundays River and four tributaries during 1996 and 1997. The redfin minnow Pseudobarbus afer comprised 81.6% of the total catch. Length frequency analysis of P. afer populations indicated recent successful recruitment in several rivers. Differences between rivers in the concentrations of dissolved and suspended solids and pH are possible reasons for different species complements. These surveys show the distribution of P. afer and Barbus aeneus in the Eastern Cape Province to be wider than previously reported. Management action is required to minimise opportunities for further establishment and spread of alien and translocated fish species and to conserve indigenous fish assemblages within the Park.