Vocal Display Research Articles

Females counter-sing, but response to male song differs by sex in Alston's singing mouse.

Vocal display behaviours are common throughout the animal kingdom, play important roles in both courtship and aggression, and are frequent subjects of behavioural research. Although females of many species vocalize, an overwhelming fraction of behavioural research has focused on male display. We investigated vocal display behaviours in female singing mice (Scotinomys teguina), small muroid rodents in which both sexes produce songs consisting of trills of rapid, downward frequency sweeps. Previous research established that male singing mice increase song production and engage in precisely timed counter-singing behaviour in response to playback of conspecific male song. We tested whether female singing mice also increased their rate of singing in response to playback of male song, whether they counter-sing, and whether there are sexual dimorphisms in song effort. Our results demonstrate that much like males, female singing mice increase their song effort and counter-sing in response to playback of male song; however, females sing fewer and shorter songs compared to males. This study further informs the understanding of female vocal behaviour and establishes the singing mouse as a valuable model for investigating female vocal display.

Does female choice for song complexity drive sexual selection in humpback whales?

Male humpback whales (Megaptera novaeangliae) sing a long, stereotyped, and culturally transmitted song display. While song likely functions in sexual selection, whether it is primarily directed at females and/or males is still debated. Most males within a single population sing the same, slowly evolving song type. However, multiple humpback whale song revolutions (where a song introduced from a neighboring population rapidly and completely replaces the existing song) have spread across the South Pacific region from the east coast of Australia to French Polynesia. How cultural evolution and sexual selection interact in this complex vocal display is not well understood. We investigated song-mediated female mate choice in humpback whales using 20 years of paternity data and song recordings from individually identified males in the small, South Pacific population of New Caledonia. As mating has never been observed in humpback whales, we assessed male reproductive success (calf paternity) and song complexity (unit repertoire and song length) of individual males. We found that males who successfully sired offspring had on average higher song complexity than males who did not sire offspring. This suggests females may select mates at least partially based on song complexity, and thus, song being primarily directed at females.

Singing more, singing harsher: occurrence of nonlinear phenomena in a primate' song.

Nonlinear phenomena (NLP) in animal vocalizations arise from irregularities in the oscillation of the vocal folds. Various non-mutually exclusive hypotheses have been put forward to explain the occurrence of NLP, from adaptive to physiological ones. Non-human primates often display NLP in their vocalizations, yet the communicative role of these features, if any, is still unclear. We here investigate the occurrence of NLP in the song of a singing primate, the indri (Indri indri),testing for the effect of sex, age, season, and duration of the vocal display on their emission. Our results show that NLP occurrence in indri depends on phonation, i.e., the cumulative duration of all the units emitted by an individual, and that NLP have higher probability to be emitted in the later stages of the song, probably due to the fatigue indris may experience while singing. Furthermore, NLP happen earlier in the vocal display of adult females than in that of the adult males, and this is probably due to the fact that fatigue occurs earlier in the former because of a greater contribution within the song. Our findings suggest, therefore, that indris may be subjected to physiological constraints during the singing process which may impair the production of harmonic sounds. However, indris may still benefit from emitting NLP by strengthening the loudness of their signals for better advertising their presence to the neighboring conspecific groups.

Variability in humpback whale songs reveals how individuals can be distinctive when sharing a complex vocal display.

Individually distinctive acoustic signals in animal vocal communication are taxonomically widespread, however, the investigation of these signal types in marine mammals has focused only on a few species. Humpback whale songs are a stereotyped, hierarchically structured vocal display performed by males, and hence thought to be sexually selected. Within a population, whales conform to a common version of the song despite the song constantly evolving. While humpback songs have been studied extensively at the population level, individual level variation has been rarely described, with inconclusive results. Here, we quantified inter- and intra-individual variability at different levels in the song hierarchy using songs from 25 singers across two song types from the eastern Australian population song of 2002 (12 singers), and the revolutionary song introduced in 2003 (13 singers). Inter-individual variability was found heterogeneously across all hierarchical levels of the song structure. In addition, distinct and individually specific patterns of song production were consistently recorded across song levels, with clear structural differences between the two song types. These results suggest that within the constraints of song conformity, males can produce individually distinctive patterns that could function as an advertisement to females to convey individual qualities.

Behavioral repertoire of the Brazilian spiny-rats, Trinomys setosus and Clyomys laticeps: different levels of sociality.

Behavior is a useful trait for comparative studies that provide the comprehension of phylogenetic relationships among species. Here, we present a description of two spiny-rats species' behavioral repertoire, Clyomys laticeps and Trinomys setosus (Rodentia: Echimyidae). The affiliative and agonistic behavioral patterns were sampled during a three-year study of captive populations of wild animals. Observational data were collected in two phases under different arrangements of individuals in groups. We also compare the behavioral traits of T. setosus and C. laticeps with the known behavioral patterns of Trinomys yonenagae. We add categories to the previous descriptions of T. setosus and a standard ethogram for C. laticeps. Trinomys setosus showed a visual and vocal display we called foot-trembling, which was not described in this form and function for other species studied until now. We discuss the differences in their sociality levels and similarities and differences among behavior patterns and repertoires.

Changes in humpback whale song structure and complexity reveal a rapid evolution on a feeding ground in Northern Norway

Singing behaviour by male humpback whales (Megaptera novaeangliae) has traditionally been associated with low-latitude breeding grounds. However, in recent years, this vocal behaviour has been increasingly reported outside these areas. All singers in a given population sing the same version of a song and this song is continually evolving over time with modifications on different levels within the song structure. Tracing changes in whale song will help to undercover the drivers underlying this vocal display and contribute to the understanding of animal culture and its evolution. To determine the progressive changes in songs found on a subarctic feeding ground and migratory stopover, a detailed analysis of humpback whale song recordings from Northern Norway was conducted. Passive acoustic data from the Lofoten-Vesterålen Ocean Observatory (LoVe), collected using a bottom-moored underwater hydrophone, were used from January - April 2018 and January 2019. Two measures of the song structure were examined: (1) sequence similarities using the Levenshtein distance and (2) song complexity using a principal component analysis (PCA). In total, 21 distinct themes were identified which presented highly directional, structural changes over time. Two themes from 2018 reoccurred in 2019, whereas all other themes in 2019 appeared to be evolved versions of 2018 themes. All songs grouped into three general clusters, reflecting the rapid evolution over the study period. With all sampled animals singing the same version of the song, this might indicate that the singers are either from the same breeding population or that song learning occurred before the study period. Song complexity appeared to follow the trend of song progression; songs became more complex as they evolved over the months in 2018 and decreased in complexity between the years, returning to a more simplified song in 2019. The results confirm that humpback whale song exhibits a rapid progression on a shared subarctic feeding ground, with strong potential for song exchange and opportunities for cultural transmission between populations in the North Atlantic.

Cultural differences in vocal expression analysis: Effects of task, language, and stimulus-related factors.

Cultural context shapes the way that emotions are expressed and socially interpreted. Building on previous research looking at cultural differences in judgements of facial expressions, we examined how listeners recognize speech-embedded emotional expressions and make inferences about a speaker’s feelings in relation to their vocal display. Canadian and Chinese participants categorized vocal expressions of emotions (anger, fear, happiness, sadness) expressed at different intensity levels in three languages (English, Mandarin, Hindi). In two additional tasks, participants rated the intensity of each emotional expression and the intensity of the speaker’s feelings from the same stimuli. Each group was more accurate at recognizing emotions produced in their native language (in-group advantage). However, Canadian and Chinese participants both judged the speaker’s feelings to be equivalent or more intense than their actual display (especially for highly aroused, negative emotions), suggesting that similar inference rules were applied to vocal expressions by the two cultures in this task. Our results provide new insights on how people categorize and interpret speech-embedded vocal expressions versus facial expressions and what cultural factors are at play.

The Yellow-breasted Barbet (Trachyphonus margaritatus) introduces vocal duets and choruses with a specific multimodal signal, during territorial advertisement

Cooperative behaviour is a prominent feature among many group-living species and continues to pose challenges to our understanding about the evolution of social relationships and task coordination between members of the same social group. Individuals who are willing to cooperate to achieve a joined action need to communicate their intentions and somehow make a common agreement. We investigated how a coordinated chorus song is initiated in a cooperative-breeding bird species, The Yellow-Breasted Barbet (Trachyphonus margaritatus). A chorus can be defined as an interactive vocal display involving several individuals who are synchronizing their behaviour to sing in a time coordinated manner. Synchronizing behaviour to sing in chorus might become quite challenging when several individuals are involved. Thus, group members could use a specific signal to induce such collective action. Yet, few studies have investigated the mechanisms of communal display initiation in chorusing bird species. We conducted playback experiments to induce and record territorial defensive reactions from birds with a video camera. We recorded 26 different groups from distinct wild populations in Djibouti which belonged to 17 sites. We found that barbets use a specific vocalization named chewp note to introduce their duet and chorus. Moreover, we found that the individual that initiates such communal displays may broadcast a multimodal signal by combining chewp note series with a typical body posture with the tail raised and fanned. We suggest that the multimodal signal could serve to attract attention and elicit a response from other group members or could enhance the song coordination.

Rutting vocal display in male impala (Aepyceros melampus) and overlap with alarm context

BackgroundThe rutting vocal display of male impala Aepyceros melampus is unique for its complexity among ruminants. This study investigates bouts of rutting calls produced towards potential mates and rival males by free-ranging male impala in Namibia. In particular, a comparison of male rutting and alarm snorts is conducted, inspired by earlier findings of mate guarding by using alarm snorts in male topi Damaliscus lunatus.ResultsRutting male impala produced 4–38 (13.5 ± 6.5) rutting calls per bout. We analyzed 201 bouts, containing in total 2709 rutting calls of five types: continuous roars produced within a single exhalation-inhalation cycle; interrupted roars including few exhalation-inhalation cycles; pant-roars distinctive by a pant-phase with rapidly alternating inhalations and exhalations; usual snorts lacking any roar part; and roar-snorts starting with a short roar part. Bouts mostly started and ended with usual snorts. Continuous roars were the shortest roars. The average duration of the exhalatory phase was longest in the continuous roars and shortest in the pant-roars. The average fundamental frequency (49.7–51.4 Hz) did not differ between roar types. Vocal tract length, calculated by using measurements of the first four vocal tract resonances (formants), ranged within 381–382 mm in all roar types. In the studied male impala, rutting snorts within bouts of rutting calls were longer and had higher values of the upper quartile in the call spectra than alarm snorts produced towards potential danger.ConclusionsAdditional inhalations during the emission of the interrupted and pant-roars prolong their duration compared to the continuous roars but do not affect the fundamental frequency or the degree of larynx retraction while roaring. Alarm snorts are separated from one another by large intervals, whereas the intervals between rutting snorts within bouts are short. Sometimes, rutting snorts alternate with roars, whereas alarm snorts do not. Therefore, it is not the acoustic structure of individual snorts but the temporal sequence and the occasional association with another call type that defines snorts as either rutting or alarm snorts. The rutting snorts of male impala may function to attract the attention of receptive females and delay their departure from a male’s harem or territory.

Cultural Transmission, Evolution, and Revolution in Vocal Displays: Insights From Bird and Whale Song.

Culture, defined as shared behavior or information within a community acquired through some form of social learning from conspecifics, is now suggested to act as a second inheritance system. Cultural processes are important in a wide variety of vertebrate species. Birdsong provides a classic example of cultural processes: cultural transmission, where changes in a shared song are learned from surrounding conspecifics, and cultural evolution, where the patterns of songs change through time. This form of cultural transmission of information has features that are different in speed and form from genetic transmission. More recently, culture, vocal traditions, and an extreme form of song evolution have been documented in cetaceans. Humpback whale song “revolutions,” where the single population-wide shared song type is rapidly replaced by a new, novel song type introduced from a neighboring population, represents an extraordinary example of ocean basin-wide cultural transmission rivaled in its geographic extent only by humans. In this review, we examine the cultural evolutions and revolutions present in some birdsong and whale song, respectively. By taking a comparative approach to these cultural processes, we review the existing evidence to understand the similarities and differences for their patterns of expression and the underlying drivers, including anthropogenic influences, which may shape them. Finally, we encourage future studies to explore the role of innovation vs. production errors in song evolution, the fitness information present in song, and how human-induced changes in population sizes, trajectories, and migratory connections facilitating cultural transmission may be driving song revolutions.

Savannah roars: The vocal anatomy and the impressive rutting calls of male impala (Aepyceros melampus) - highlighting the acoustic correlates of a mobile larynx.

A retractable larynx and adaptations of the vocal folds in the males of several polygynous ruminants serve for the production of rutting calls that acoustically announce larger than actual body size to both rival males and potential female mates. Here, such features of the vocal tract and of the sound source are documented in another species. We investigated the vocal anatomy and laryngeal mobility including its acoustical effects during the rutting vocal display of free‐ranging male impala (Aepyceros melampus melampus) in Namibia. Male impala produced bouts of rutting calls (consisting of oral roars and interspersed explosive nasal snorts) in a low‐stretch posture while guarding a rutting territory or harem. For the duration of the roars, male impala retracted the larynx from its high resting position to a low mid‐neck position involving an extensible pharynx and a resilient connection between the hyoid apparatus and the larynx. Maximal larynx retraction was 108 mm based on estimates in video single frames. This was in good concordance with 91‐mm vocal tract elongation calculated on the basis of differences in formant dispersion between roar portions produced with the larynx still ascended and those produced with maximally retracted larynx. Judged by their morphological traits, the larynx‐retracting muscles of male impala are homologous to those of other larynx‐retracting ruminants. In contrast, the large and massive vocal keels are evolutionary novelties arising by fusion and linear arrangement of the arytenoid cartilage and the canonical vocal fold. These bulky and histologically complex vocal keels produced a low fundamental frequency of 50 Hz. Impala is another ruminant species in which the males are capable of larynx retraction. In addition, male impala vocal folds are spectacularly specialized compared with domestic bovids, allowing the production of impressive, low‐frequency roaring vocalizations as a significant part of their rutting behaviour. Our study expands knowledge on the evolutionary variation of vocal fold morphology in mammals, suggesting that the structure of the mammalian sound source is not always human‐like and should be considered in acoustic analysis and modelling.

Convergence to the tiniest detail: vocal sac structure in torrent-dwelling frogs

Abstract Cascades and fast-flowing streams impose severe restrictions on acoustic communication, with loud broadband background noise hampering signal detection and recognition. In this context, diverse behavioural features, such as ultrasound production and visual displays, have arisen in the evolutionary history of torrent-dwelling amphibians. The importance of the vocal sac in multimodal communication is being increasingly recognized, and recently a new vocal sac visual display has been discovered: unilateral inflation of paired vocal sacs. In the diurnal stream-breeding Hylodidae from the Atlantic forest, where it was first described, this behaviour is likely to be enabled by a unique anatomical configuration of the vocal sacs. To assess whether other taxa share this exceptional structure, we surveyed torrent-dwelling species with paired vocal sacs across the anuran tree of life and examined the vocal sac anatomy of exemplar species across 18 families. We found striking anatomical convergence among hylodids and species of the distantly related basal ranid genera Staurois, Huia, Meristogenys and Amolops. Ancestral character state reconstruction identified three new synapomorphies for Ranidae. Furthermore, we surveyed the vocal sac configuration of other anuran species that perform visual displays and report observations on what appears to be unilateral inflation of paired vocal sacs, in Staurois guttatus – an extremely rare behaviour in anurans.

The devil is in the detail: Quantifying vocal variation in a complex, multi-levelled, and rapidly evolving display.

Identifying and quantifying variation in vocalizations is fundamental to advancing our understanding of processes such as speciation, sexual selection, and cultural evolution. The song of the humpback whale (Megaptera novaeangliae) presents an extreme example of complexity and cultural evolution. It is a long, hierarchically structured vocal display that undergoes constant evolutionary change. Obtaining robust metrics to quantify song variation at multiple scales (from a sound through to population variation across the seascape) is a substantial challenge. Here, the authors present a method to quantify song similarity at multiple levels within the hierarchy. To incorporate the complexity of these multiple levels, the calculation of similarity is weighted by measurements of sound units (lower levels within the display) to bridge the gap in information between upper and lower levels. Results demonstrate that the inclusion of weighting provides a more realistic and robust representation of song similarity at multiple levels within the display. This method permits robust quantification of cultural patterns and processes that will also contribute to the conservation management of endangered humpback whale populations, and is applicable to any hierarchically structured signal sequence.

On the natural history of duetting in White-browed Coucals: sex- and body-size-dependent differences in a collective vocal display

Avian duets have long fascinated biologists, but much remains unknown about what information may be contained in these collective displays and how duet structures vary between taxa. In this study, we describe the structure and performance rules of duets in White-browed Coucals Centropus superciliosus, a tropical non-parasitic Cuckoo. We recorded vocal behaviours of 11 focal pairs and measured temporal, frequency, and amplitude characteristics of their duets. Molecular sexing and radio telemetry revealed that duets were initiated by both sexes, but the majority of them were led by the male. Moreover, we found that duet contributions were sex specific with females producing lower-pitched songs than males, reflecting the general size dimorphism in this species. Finally, we also found that song peak frequencies varied with body size within each sex, suggesting that songs used in duets may act as index signals of body size. We speculate that sexual selection has driven White-browed Coucals to sing as low as possible, a notion that is further supported by our observation of special singing postures that may help in lowering song pitch even further.

Positive association between vocal and facial attractiveness in women but not in men: A cross-cultural study

Various species use multiple sensory modalities in the communication processes. In humans, female facial appearance and vocal display are correlated and it has been suggested that they serve as redundant markers indicating the bearer’s reproductive potential and/or residual fertility. In men, evidence for redundancy of facial and vocal attractiveness is ambiguous. We tested the redundancy/multiple signals hypothesis by correlating perceived facial and vocal attractiveness in men and women from two different populations, Brazil and the Czech Republic. We also investigated whether facial and vocal attractiveness are linked to facial morphology. Standardized facial pictures and vocal samples of 86 women (47 from Brazil) and 81 men (41 from Brazil), aged 18–35, were rated for attractiveness by opposite-sex raters. Facial and vocal attractiveness were found to positively correlate in women but not in men. We further applied geometric morphometrics and regressed facial shape coordinates on facial and vocal attractiveness ratings. In women, facial shape was linked to their facial attractiveness but there was no association between facial shape and vocal attractiveness. In men, none of these associations was significant. Having shown that women with more attractive faces possess also more attractive voices, we thus only partly supported the redundant signal hypothesis.

Elaborate Mimetic Vocal Displays by Female Superb Lyrebirds

Some of the most striking vocalizations in birds are made by males that incorporate vocal mimicry in their sexual displays. Mimetic vocalization in females is largely undescribed, but it is unclear whether this is because of a lack of selection for vocal mimicry in females, or whether the phenomenon has simply been overlooked. These issues are thrown into sharp relief in the superb lyrebird, Menura novaehollandiae, a basal oscine passerine with a lek-like mating system and female uniparental care. The spectacular mimetic song display produced by courting male lyrebirds is a textbook example of a sexually selected trait, but the vocalizations of female lyrebirds are largely unknown. Here, we provide the first analysis of the structure and context of the vocalizations of female lyrebirds. Female lyrebirds were completely silent during courtship; however, females regularly produced sophisticated vocal displays incorporating both lyrebird-specific vocalizations and imitations of sounds within their environment. The structure of female vocalizations varied significantly with context. While foraging, females mostly produced a complex lyrebird-specific song, whereas they gave lyrebird-specific alarm calls most often during nest defense. Within their vocal displays females also included a variety of mimetic vocalizations, including imitations of the calls of dangerous predators, and of alarm calls and song of harmless heterospecifics. Females gave more mimetic vocalizations during nest defense than while foraging, and the types of sounds they imitated varied between these contexts, suggesting that mimetic vocalizations have more than one function. These results are inconsistent with previous portrayals of vocalizations by female lyrebirds as rare, functionless by-products of sexual selection on males. Instead, our results support the hypotheses that complex female vocalizations play a role in nest defense and mediate female-female competition for breeding territories. In sum, this study reveals elaborate female vocal displays in a species widely depicted as an example of sexual selection for male extravagance, and thus highlights the hidden complexity of female vocalizations.

Bioacoustic cues and their relations to dominance rank in Père David’s deer stags

The vocal display of male animals during the breeding season has received particular attention. To find out whether male acoustic signals could be a quality-assessment cue of callers, we conducted a study on Père David’s deer (Elaphurus davidianus) characterised by a polygynous mating system and high male–male competition during the rutting season. We investigated the relationship between the stag’s acoustic properties and the dominance rank as an indication of quality. Results showed that (1) there were two types of calls, the common roar and the chasing bark, (2) there was no significant difference between the call duration of the common roar and the chasing bark among different dominance ranks, (3) in the common roar, the value of the fundamental frequency, formant frequencies and formant spacing decreased significantly with the rise of dominance ranks and (4) vocal intensity of the common roar differed significantly among the three dominance ranks such as the harem master, the challengers and the bachelors. Our results suggested that some acoustic features, such as formant frequencies, formant spacing and vocal intensity of the common roar were closely related to the dominance rank and could be effective indicators of male competitive ability.

The Filth and the Fury: An Essay on Punk Rock Heavy Metal Karaoke

Lauren is a photographer who lives in New York City. The daughter of a urologist, she grew up in Westchester County and graduated cum laude from NYU. Lauren's master's degree in photography has served her well at Punk Rock Heavy Metal Karaoke (PMK), a live band karaoke night in New York City she attends almost every week. (1) The gaze of her camera is frequently trained on friends and strangers as they sing, scream, and pose onstage. With over one hundred of her photos posted online, this is still only a small portion of the thousand-plus PMK photos on the photo-sharing website flickr.com. In documenting this amateur event, Lauren is also joined by a host of videographers, including a number of professionals. PMK has inspired a documentary film that played the independent festival circuit, Punk Rock Heavy Metal Karaoke: The Movie (2001), and videos of individual singers have been uploaded on YouTube. (2) The joy found in looking and being looked at is a big part of PMK's appeal, and, as one might expect, hearing and being heard is also central to the event. Every week the voice is "gazed" upon by listeners much as the body is gazed upon by spectators. A great deal of attention focuses on how individual singers emulate the original vocalist of a song and the degree to which they stake out a vocal identity of their own, as well as how they present themselves in relation (or contrast) to familiar rock star visual codes. The power of this bodily and vocal display is illustrated one Monday night as Lauren prepares to venture into the more aggressive reaches of the punk songlist. Having previously limited herself to a handful of pop-tinged songs--songs that are in keeping with her friendly offstage demeanor--Lauren has taken a bit of ribbing for her ever-present smile and what one PMK regular, Rico, calls her "aura of niceness." So when Rico dares her to sing "something with the words 'fuck,' 'cunt,' or 'abortion,'" whether intended as a joke or not, she decides to accept the challenge. After the emcee calls Lauren's name, she nervously accepts the microphone and the beer-stained plastic-sheathed lyric sheet. As the band launches into a stampeding, overdriven two-note riff Lauren's eyes intensify and she spits out the words: I'VE FUCKED A SHEEP AND I'VE FUCKED A GOAT! I RAMMED MY COCK RIGHT DOWN ITS THROAT! SO WOT?! SO WOT?! SO WOT SO WOT YEW BORING LITTLE CUNT! In the act of singing "So What" by Anti-Nowhere League ([1981] 1996), (3) Lauren's entire demeanor changes. The smile remains but there is a visible gleam of malice in her eye. On the small stage her body is propelled forward as she moves aggressively toward the audience. Likewise her voice is cast out of her body with a shrieking force that twists the simple melody of the song into new shapes. The reaction of the audience to Lauren's new persona is overwhelming positive. Those nearest the stage gaze up and scream the next lines together, ending with an accusatory "WHO CARES ABOUT YOU! YOU! YOU! YOU!" as they point alternately toward the stage and each other. At the song's end, after Lauren has sung about her further adventures "spewing up on a pint of piss," "jacking up until [she] bleed[s]," "suck[ing] an old man's cock," and "fuck[ing] a schoolgirl's crack," the audience breaks out into rapturous applause and approving catcalls. By her own admission, singing "So What" for the first time destabilizes Lauren's sense of discrete selfhood. Afterwards, she describes feeling "momentarily possessed" by her newly discovered "dark side," letting out "a devilish fit of laughter" when she left the stage. Even a couple of years later, in a quote taken from her wedding announcement (she married the karaoke band's drummer), Lauren describes the PMK experience in similar terms: "it unleashed something I never knew existed." Drawing on imagery appropriate to a horror movie, she could just as easily be describing The Exorcist and its depiction of a young girl whose body and voice become instruments of the Devil. …

Information Retention During Competitive Interactions: Siblings Need to Constantly Repeat Vocal Displays

Memory is essential to adjust behaviour according to past experience. In societies where animals interact on numerous occasions, memory of previous social interactions may help optimise investment in competition. How long information about the resource holding potential and motivation to compete of conspecifics is retained depends on how fast the value of this information fades, but also on the cost and benefit of retaining information. Information retention has never been investigated in the context of interactions prevailing within the family and more specifically sibling competition. In the absence of parents, barn owl (Tyto alba) nestlings vocally compete for priority of access to the next indivisible food item brought by a parent. The finding that owlets eavesdrop on vocal interactions between siblings to adjust investment in vocalization once competing with them suggests that they memorize siblings’ vocal interactions. Playback experiments showed that owlets take into account the past siblings’ vocal performance that signals hunger for at least 15 min, but only if the performance was witnessed during a sufficiently long period of time (30 min). Moreover, using natural vocal exchanges in another set of individuals, we showed that sibling signalling was no more taken into account after a few minutes. This suggests that young barn owls need to continuously display their motivation to trigger siblings’ withdrawal from the current competition. Repeating a vocal display may ensure its honesty. Studying the extent to which individuals retain past information is important to understand how individuals adjust their competitive investment over resources.

Source levels of the underwater calls of a male leopard seal.

Leopard seals (Hydrurga leptonyx) are top predators in the Antarctic ecosystem. They produce stereotyped calls as part of a stylized underwater vocal display. Understanding of their acoustic behavior is improved by identifying the amplitude of their calls. The amplitude of five types of calls (n = 50) from a single male seal were measured as broadband source levels and ranged from 153 to 177 dB re 1 μPa at 1 m. The mean source levels differed between call types, the lower frequency calls (L, D, and O) tended to have source levels 10 dB higher than the higher frequency calls (H and M). Information on call-type source levels is important to take into account for passive acoustic studies investigating repertoire usage as calls produced with greater amplitudes are likely to have larger acoustic ranges, especially when these are also the calls with lower frequencies, such as is the case in leopard seals.