Acoustic emissions of Sorex unguiculatus (Mammalia: Soricidae): Assessing the echo‐based orientation hypothesis

Shrew species have been proposed to utilize an echo‐based orientation system to obtain additional acoustic information while surveying their environments. This system has been supported by changes in vocal emission rates when shrews encounter different habitats of varying complexity, although detailed acoustic features in this system have not been reported. In this study, behavioral experiments were conducted using the long‐clawed shrew (Sorex unguiculatus) to assess this orientation system. Three experimental conditions were set, two of which contained obstacles. Short‐click, noisy, and different types of tonal calls in the audible‐to‐ultrasonic frequency range were recorded under all experimental conditions. The results indicated that shrews emit calls more frequently when they are facing obstacles or exploring the experimental environment. Shrews emitted clicks and several different types of tonal calls while exploring, and modified the use of different types of calls for varying behavior. Furthermore, shrews modified the dominant frequency and duration of squeak calls for different types of obstacles, that is, plants and acrylic barriers. The vocalizations emitted at short inter‐pulse intervals could not be observed when shrews approached these obstacles. These results are consistent with the echo‐based orientation hypothesis according to which shrews use a simple echo‐orientation system to obtain information from their surrounding environments, although further studies are needed to confirm this hypothesis.     

Call recognition and female choice in a treefrog with a multicomponent call

Acoustic mating signals are typically species‐specific, and often additionally are subject to directional female preferences. Male executioner treefrogs, Dendropsophus carnifex, produce a multicomponent advertisement call composed of an introductory screech note followed by two or more click notes. Here, we tested (i) call recognition by comparing female directed phonotaxis towards individual and combined call components: screech vs. clicks vs. screech + clicks, (ii) female preferences for greater numbers of click notes and (iii) female preferences for faster call rates. The results demonstrated that screeches and clicks, presented either separately or together as a complete call, evoke similar female responses, suggesting that either note was sufficient to elicit a mate‐recognition response. Additionally, females preferred calls with greater numbers of click notes and with faster call rates. We interpret these results within the context of female mate selection in natural choruses.     

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ABSTRACT

In most mammals, adults produce relatively low frequency vocalizations compared to those of juveniles. This rule is not maintained however at least in four species of ground squirrels, whose juveniles call at the adult's fundamental frequency. These findings have been obtained however with separate sets of juveniles and adults and no data is available concerning the ontogeny linked to these differences. Here we analyze the acoustic structure of alarm calls of the same Yellow Spermophilus fulvus and Speckled S. suslicus ground squirrel individuals, recorded as pups and as adults after hibernation. We found the fundamental frequencies of adults within the same frequency ranges as those of pups, in spite of the significant difference in body mass. In ground squirrels, severing the relationship between body size and call frequency removes some vocal cues to age. We discuss some functional hypotheses advanced to explain manipulations with fundamental frequencies in ground squirrels and other animals, and suggest the lack of data for discussing the mechanisms of such vocal tuning.     

人为疼痛刺激下金色中仓鼠幼鼠叫声的发育过程

金色中仓鼠幼鼠可以利用可听声和超声信号与母鼠进行交流,这些声音可以反映个体的寒冷、饥饿、疼痛等不同生理状态和需求。因疼痛诱发的叫声对于维持幼鼠的存活也有着重要意义。本实验通过录制人为疼痛刺激下,不同日龄金色中仓鼠的叫声,分析并比较了5 - 30 日龄金色中仓鼠不同发声信号特征(可听声出现频次、可听声持续时程、可听声主频率、超声出现频次、超声持续时程、超声主频率)的性别差异;同时记录了幼鼠的两种发声随日龄的变化趋势。结果发现:幼鼠两种叫声的各种参数均未表现性二型现象。幼鼠超声发生频次随日龄增加而逐渐减少。而可听声却正相反,随日龄增加而逐渐上升,并在20 日龄时达到最高峰,之后逐渐下降。可听声持续时程也随日龄而增加。综上,在人为疼痛刺激下,随着日龄增加,幼鼠更倾向于使用可听 声而非超声与母兽进行交流。     

Biphonation May Function to Enhance Individual Recognition in the Dhole, Cuon alpinus

Biphonation (two independent fundamental frequencies in a call spectrum) represents one of the most widespread nonlinear phenomena in mammalian vocalizations. Recently, the structure of biphonations was described in detail; however, their functions are poorly understood. For the dhole (Cuon alpinus), biphonic calls represent a prominent feature of vocal activity. In this species, the biphonic call is composed of two frequency components – the high‐frequency squeak and the low‐frequency yap, which also occur alone as separate calls. In this study, we test the hypothesis that the complication of call structure, resulting from the joining of these calls into the biphonic yap–squeak may enhance the potential for individual recognition in the dhole. We randomly selected for analysis 30 high‐frequency squeaks, 30 low‐frequency yaps and 30 biphonic yap–squeaks per animal from five subadult captive dholes (450 calls in total). Discriminant analysis, based on 10 squeak parameter values, showed 80.7% correct assignment to a predicted individual. For 10 yap parameters, the correct assignment was only 44.7%. However, the analysis based on 10 parameters of the biphonic yap–squeak, selected as best contributing to discrimination, showed 96.7% correct assignment to a predicted individual. The results provide strong support for the hypothesis tested showing that the joining of two independent calls into a common vocalization may function to enhance individual recognition in the dhole.     

Vocal behavior of Great Curassows,a vulnerable Neotropical bird

ABSTRACT The Cracidae rank among the most threatened families of Neotropical birds, and studies of their vocal behavior may help guide conservation and monitoring efforts. We describe the vocal behavior of Great Curassows (Crax rubra), a little‐studied Cracid species currently listed as vulnerable. From 2008 to 2010, we recorded curassows in northwest Costa Rica using both handheld and automated digital recorders. Analysis of recordings revealed that Great Curassows had a vocal repertoire of five call types. Yip and bark calls are sex‐specific alarm calls of short duration (0.12 and 0.08 s, respectively). The descending whistle is a longer duration alarm call (2.18 s) produced primarily by males. The snarl is a short call (0.67 s) associated with a threat display produced by adults with dependent young. The boom call was the most common Great Curassow vocalization, and was given only by males. Boom calls are long (8.86 s), low‐frequency (<150 Hz), multisyllable calls comprised of four stereotyped phrases. Great Curassows often uttered boom calls well before dawn, with a peak in activity at dawn and the hours following. Males produced bouts of repeated boom calls that lasted an average of 35 min, but sometimes continued for more than 5 h. Boom calls were given from February to June, with a peak in late April and early May when breeding begins. Discriminant analysis of boom calls of birds from 10 different locations revealed interindividual variation in call structure that may be useful for bioacoustic monitoring of individuals. Our results suggest that automated recorders might provide a way to monitor the abundance of male curassows because their boom calls are given frequently during the period from February to June and can be detected at distances up to 250 m.     

Clicks and Communication: The Behavioural and Social Contexts of Hector's Dolphin Vocalizations

Hector's dolphins (Cephalorhynchus hectori) have a simple vocal repertoire, consisting almost entirely of ultrasonic clicks. They produce no whistles, and very few audible sounds. To examine acoustic communication in this species I analysed the relationship between click types and behaviour. The proportion of complex click types was greater in large groups, suggesting that these sounds have social significance. Clicks having 2 peaks in their time envelope and two frequency peaks were strongly associated with behaviours indicative of feeding. High pulse rate sounds, in which the repetition rate of ultrasonic clicks was audible as a “cry”, were most strongly associated with aerial behaviours. These data suggest that echo-location is not the sole function of Hector's dolphin clicks, and that echo-location and communication are likely to be closely linked. I hypothesize that dolphins may have the ability to gather information from the echoes of each other's sonar pulses. This may reduce the need for a large number of vocal signals, and may explain the apparent simplicity of the acoustic repertoires of some odontocetes.     

Development of echolocation and communication vocalizations in the big brown bat, <Emphasis Type="Italic">Eptesicus fuscus</Emphasis>

Big brown bats form large maternity colonies of up to 200 mothers and their pups. If pups are separated from their mothers, they can locate each other using vocalizations. The goal of this study was to systematically characterize the development of echolocation and communication calls from birth through adulthood to determine whether they develop from a common precursor at the same or different rates, or whether both types are present initially. Three females and their six pups were isolated from our captive breeding colony. We recorded vocal activity from postnatal day 1 to 35, both when the pups were isolated and when they were reunited with their mothers. At birth, pups exclusively emitted isolation calls, with a fundamental frequency range <20 kHz, and duration >30 ms. By the middle of week 1, different types of vocalizations began to emerge. Starting in week 2, pups in the presence of their mothers emitted sounds that resembled adult communication vocalizations, with a lower frequency range and longer durations than isolation calls or echolocation signals. During weeks 2 and 3, these vocalizations were extremely heterogeneous, suggesting that the pups went through a babbling stage before establishing a repertoire of stereotyped adult vocalizations around week 4. By week 4, vocalizations emitted when pups were alone were identical to adult echolocation signals. Echolocation and communication signals both appear to develop from the isolation call, diverging during week 2 and continuing to develop at different rates for several weeks until the adult vocal repertoire is established.     

Discomfort-related changes in pup ultrasonic calls of fat-tailed gerbils Pachyuromys duprasi

Rodent pups vocalize when placed in social isolation. We apply a method of “joint calls” for examining discomfort in rodent pup ultrasonic (>20 kHz) calls. Previously, this method has been developed for audible calls of fur farm mammals. Using a repeated measures design to exclude effects of individual identity and age on the analysed variables, we compared the ultrasonic call variables produced by 8–40-day pups of fat-tailed gerbils Pachyuromys duprasi during two subsequent experimental stages, the Isolation Stage and the Handling Stage. We considered that discomfort-related negative emotional arousal increased towards the Handling Stage compared to the Isolation Stage because of cumulative effects of handling and time of pup isolation from the nest. At the Isolation Stage, the call rate (calls/s) was higher from 10 to 18 days of age, whereas both the maximum amplitude frequency and power quartiles of joint calls were lower than at the Handling Stage from 20 to 32 days of age. At the same time, in audible (<20 kHz) vocalizations of a wide range of mammalian species, both the higher call rate and the upward shift of the maximum amplitude frequency and power quartiles indicate the discomfort-related increase of negative emotional arousal. We discuss the advantages of the method of joint calls for express-analyses of power variables for large sequences of ultrasonic vocalizations of complex acoustic structure during experimental trials.     

Species-specific and shared features in vocal repertoires of three Eurasian ground squirrels (genus <Emphasis Type="Italic">Spermophilus</Emphasis>)

Along to alarm calls, Eurasian ground squirrels of the genus Spermophilus also produce other call types toward potential predators and rival conspecifics. Individually identified 50 speckled (Spermophilus suslicus), 18 European (S. citellus) and 59 yellow (S. fulvus) ground squirrels were examined for interspecies differences in their vocal repertoires. A separate sample of 116 (90 adult and 26 juvenile) S. suslicus was examined for presence of ultrasound in their alarm calls. In addition, all tonal calls in all the three species were checked for presence of nonlinear phenomena. Calls were elicited by approaching animals in live-traps or near burrows; some types of vocalizations were also recorded during handling. Eight call types, three tonal and five wideband ones, were described. Vocal repertoires were remarkably similar between species, excluding the alarm calls, which were species-specific. Alarm calls with ultrasonic components were found in two individuals of S. suslicus. Concerning nonlinear phenomena, biphonation in alarm calls of S. suslicus, frequency jumps and sidebands in screams of S. citellus, frequency jumps and subharmonics in screams of S. fulvus were found. Results are discussed with literature evidence on audible and ultrasonic vocalizations in ground squirrels.     

Repeated call types in short‐finned pilot whales,Globicephala macrorhynchus

Four short‐finned pilot whales, Globicephala macrorhynchus, were tagged with digital acoustic recording tags (DTAGs) for a total of 30 h in the Bahamas during 2007. Spectrograms were made of all audible sounds, which were independently categorized by three observers. Of 4,098 calls, 1,737 (42%) were placed into 173 call types, which were defined as calls that occurred more than once. Of the 173 call types, 51 contained at least 10 calls (= 24), and were termed predominant call types (PCTs), which comprised 1,219 (70%) of categorized calls. PCTs tended to occur in sequences of the same call, which appeared to be produced by a single animal. However, matching interactions consisting of adjacent or overlapping calls of the same type were also observed, and some call types were recorded on more than one tag, suggesting that at least some calls are shared by members of a group or subgroup. These results emphasize the importance of categorizing calls before attempting to draw conclusions about call usage and possible effects of noise on vocal behavior.     

Vocal repertoire ontogeny of the captive Asian house shrew Suncus murinus suggests that the male courtship call develops from the caravanning call of the young

Soricids produce a considerable variety of vocalizations. However, these calls have been studied insufficiently with the exception of echolocation calls. In this study, 1,645 calls from 18 juvenile, ten sub-adult and 36 adult Asian house shrews (Suncus murinus) were acoustically and statistically analyzed to describe this species’ vocal repertoire and its ontogeny. The vocal repertoire of S. murinus includes 17 call types, seven tonal (whistle, chirp, twitter, whimper, squeak, scream and short scream) and ten non-tonal (churr, shriek, babble, click, boom, snort, screech, short screech, sniff and low click), of which ten call types (whimper, squeak, scream, short scream, churr, babble, snort, short screech, sniff and low click) were newly described by this study. This relatively extensive vocal repertoire, including one call type emitted during collective resting, indicates that this species possibly possesses a higher degree of sociality and cohesiveness than previously expected. High structural similarities were observed between calls produced by juveniles and sub-adults during caravanning and those produced by adult males during courtship. Therefore, the results of this study support a previously suggested hypothesis that in shrews, adult courtship calls are derived from calls emitted by the young. The results of this study also showed that the largest changes in the ontogeny of the vocal repertoire occurred at approximately 10 days old and was in close connection to the eyes opening. The results are discussed with available information on the vocal repertoires of other soricids.     

The Vocal Repertoire of Barbary Macaques: A Quantitative Analysis of a Graded Signal System

The vocal behavior of Barbary macaques (Macaca sylvanus) was studied in an outdoor enclosure at Rocamadour, France. Ad libitum recordings were made across a broad array of socioecological contexts from 92 individually identified subjects from all age—sex classes. From the recordings, 8479 calls were sampled and submitted to a Fourier transform. A custom software program was used to determine 35 acoustic parameters describing the call in terms of its frequency and time dynamics. On these parameters a cluster analysis was used to examine the acoustic morphology of the Barbary macaque vocal repertoire. The analysis revealed a highly graded structure with intergraded variations between different clusters (‘call types’). There were clear age-related preferences in usage of different clusters, but animals of all ages were potentially able to produce the whole array of call types. The major sex difference was a differential use of certain call types in specific situations. Despite a clear sex dimorphism in body size no significant sex differences in the acoustic structure of calls in adults was found. There were no unidirectional relationships between the acoustic structure of a call and the context in which it was uttered, although call usage was more specific in some contexts than in others. The results suggest that the major factor underlying the variation in acoustic structure reflect the internal state of the caller.     

Spectrographic Description of Vocalizations in Captive Otolemur garnettii

To advance knowledge of the vocal communication associated with close proximity social interactions in Garnett's greater bush baby (Otolemur garnettii), we measured acoustic and temporal properties of vocalizations from videotaped recordings of captives in two main social contexts: mother-infant interactions and adult male-female pair introductions and reintroductions. We used a real-time sonagraph or software program to display, edit, and analyze vocal waveforms, and to provide wideband and narrowband spectrograms. Vocalization characteristics measured include fundamental frequency (via inspection of harmonics) and spectral features such as formant frequency, intensity, and duration. The vocal repertoire contained 4 major types of vocalizations: 1) barks and complex multiple bark sequences, 2) low frequency flutter/hums and growls, 3) high frequency clicks and spits, and 4) noisy shrieks. We describe several vocalizations for the first time and provide a clear classification of some of them on the basis of call durations (long/short growls). Complex bark sequences, previously described as distant communication calls, were invariant and were not often emitted by individuals when in close proximity. When classified spectrographically, the remaining 3 call types, which occurred when individuals were in close proximity, were less stereotypical, and gradations within call types were apparent. Our results show that although nocturnal and non-gregarious, complex communicatory signals of bush babies constitute a vocal repertoire formerly thought to be characteristic only of diurnal, gregarious primates.     

Individual variation in the isolation calls of Mexican free-tailed bat pups (Tadarida brasiliensis mexicana)

Near-term pregnant females and female-pup nursing pairs of Mexican free-tailed bats (Tadarida brasiliensis mexicana) were captured from large maternity colonies in central Texas. A total of 337 isolation calls from 20 pups were recorded and nine call parameters were measured from each call either sonagraphically or with a spectrum analyser. Univariate and multivariate analyses of the call parameters show that the calls of different pups are structurally distinct. Discriminant function analysis using a random subset of calls correctly categorized 60·4% to the pup emitting them. These results suggest that the pups have individual vocal signatures. Calls also possess qualities which suggest that they are attractive in nature and easy to locate. Regression analyses show that several call parameters increase in frequency as pups age.     

INDIVIDUAL VARIATION OF THE FEMALE ATTRACTION CALL PRODUCED BY AUSTRALIAN FUR SEAL PUPS THROUGHOUT THE MATERNAL DEPENDENCE PERIOD

ABSTRACT

Australian fur seals are colonial breeding animals that give birth on crowded rookeries. Females leave their pups unattended for extended periods while they forage at sea. On return to the colony, a mother must relocate her pup amongst the hundreds of other pups. Vocal recognition is thought to play a vital role in maintaining the mother-pup bond. In the present study, four sets of 7 different pups were recorded once each at different times throughout the maternal dependence period. The Female Attraction Call was used to determine whether Australian fur seal pups produce individually distinct calls which could be used as a basis for vocal recognition. Results from three different analyses (PIC, DFA and CART) indicated that the fundamental frequency, number of parts per call, duration, quavering and peak frequency changes at the start, mid-point and end of the call (i.e., along PEAK Fl) were important to recognition. In 75% of cases using DFA, the Female Attraction Call was classified to the correct caller, suggesting that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition by females.     

Elephant calling patterns as indicators of group size and composition: the basis for an acoustic monitoring system

The paper gives evidence that the vocal activity of elephants varies with group size, composition and reproductive status, and that elephants' calling patterns could therefore provide the basis for a remote monitoring system. We examined a 3‐week set of array‐based audio recordings of savanna elephants (Loxodonta africana), searching for diagnostic acoustic parameters. An acoustic array made it possible to locate recorded sounds and attribute the calls to particular elephants or elephant groups. Simultaneous video recordings made it possible to document visible behaviour and roughly correlate it with vocalizations. We compared several measures of call density in elephant groups containing up to 59 individuals, and found that rates of calling increased with increasing numbers of elephants. We divided all call events into three structural types (single‐voice low‐frequency calls, multiple‐voice clustered low‐frequency calls, and single‐voice high frequency calls), and found that the incidence of these varies predictably with group composition. These results suggest the value of a network of listening systems in remote areas for the collection of information on elephant abundance and population structure.     

Characterization of Australian fur seal vocalizations during the breeding season

The vocal repertoire, structure, and behavioral context of airborne vocalizations produced by Australian fur seals (Arctocephalus pusillus doriferus) are described using recordings made at a breeding colony on Kanowna Island, Bass Strait, Australia. The study identified six different call types: three produced by males (bark, guttural threat, and submissive call); five produced by females (bark, guttural threat, submissive call, growl, and pup attraction call) and the female attraction call produced by pups and yearlings. Vocalizations were compared according to age and sex classes. The overall structure and function of the pup attraction and female attraction call produced by females, yearlings, and pups, was similar. However, while similar in their overall appearance, certain call types have a lower fundamental frequency when compared with other fur seals. In addition, the male bark call alters in rate of production according to the context used, where calls are slower when males are stationary and advertising their territorial status and faster when males are involved in confrontations with other males or actively herding females. Further research is required to investigate changes in environmental conditions and their effects on shaping the call structure and communication in Australian fur seals.