Sound or Silence: Call Recognition in the Temporal Domain by the Frog Allobates femoralis

Acoustic communication often mediates agonistic interactions in territorial species. Because both the reaction to potential intruders and the lack thereof are costly, mechanisms that allow recognition of conspecific signals should be evident in intrasexual communication systems. While the spectral domain of the recognition space of the frog Allobates femoralis appears asymmetrically shaped in a way that reduces masking interference by the often syntopic frog Ameerega trivittata, frequency alone does not appear to account for the correct identification of conspecific intruders (Amézquita et al., Animal Behaviour, 70, 2005: 1377). As signal recognition may rely on a combination of spectral and temporal parameters of the signal, we test here the subsequent prediction that the recognition space should be asymmetrical in the temporal domain as well. We conducted playback experiments with 80 synthetic calls on 30 males and modeled all‐or‐none responses to define unidimensional functions of the recognition space for two call parameters: note duration and internote interval. For both parameters, male maximal response matched very well the average values of the conspecific signal and decreased with concomitant deviations from these values. While the response curves exceeded the range of signal variation and were not asymmetrical for either call parameter, they differed in breadth. The highest male permissiveness to variation in internote interval, as evidenced by a broader response curve, coincided with the lower probability of between‐species overlap in this signal parameter. Together with previous studies, our data suggest that a combination of spectral and temporal parameters of the advertisement call is necessary for recognition of calling intruders in A. femoralis. Our results emphasize the importance of multidimensional approaches in understanding signal recognition mechanisms in acoustically complex environments.     

Complex Vocal Responses to Conspecific Calls in Whistling Frogs Eleutherodactylus johnstonei: Playback Experiments in the Field

We simulated the presence of an acoustic competitor by broadcasting conspecific playbacks to males of Johnstone's whistling frog, Eleutherodactylus johnstonei, in the field. We broadcast calls that differed in duration (short, typical, and long), dominant frequency (high, typical, and low), and period (short, typical, and long), and analyzed male vocal responses. We tested the hypothesis that males respond by escalating vocally when they are exposed to female‐attractive calls and by ignoring unattractive ones. At the population level, males responded to playbacks in ways that would potentially increase their attractiveness with regard to solo calling: males increased the duration, reduced the dominant frequency, and increased their calling effort (duty cycle), despite an increase in call period. The modification of call duration occurred only in response to playbacks of low‐frequency calls, long calls, and short‐period calls (selective response), while the modification of the dominant frequency was independent of the characteristic of the playback (fixed response). Contrary to the expected, males did not reduce the call period when they were exposed to attractive playbacks. At the ultimate level, the results suggest energy‐saving strategies. In addition, males seem to trade off call period for the avoidance of acoustic interference with attractive calls as calling effort was typically increased by increasing call duration but only rarely by reducing the call period. Interactive playbacks are necessary to better understand the calling strategies of males of E. johnstonei.     

Masking interference and the evolution of the acoustic communication system in the Amazonian dendrobatid frog Allobates femoralis

The efficacy of communication relies on detection of species-specific signals against the background noise. Features affecting signal detection are thus expected to evolve under selective pressures represented by masking noise. Spectral partitioning between the auditory signals of co-occurring species has been interpreted as the outcome of the selective effects of masking interference. However, masking interference depends not only on signal's frequency but on receiver's range of frequency sensitivity; moreover, selection on signal frequency can be confounded by selection on body size, because these traits are often correlated. To know whether geographic variation in communication traits agrees with predictions about masking interference effects, we tested the hypothesis that variation in the male-male communication system of the Amazonian frog, Allobates femoralis, is correlated with the occurrence of a single species calling within an overlapping frequency range, Epipedobates trivittatus. We studied frogs at eight sites, four where both species co-occur and four where A. femoralis occurs but E. trivittatus does not. To study the sender component of the communication system of A. femoralis and to describe the use of the spectral range, we analyzed the signal's spectral features of all coactive species at each site. To study the receiver component, we derived frequency-response curves from playback experiments conducted on territorial males of A. femoralis under natural conditions. Most geographic variation in studied traits was correlated with either call frequency or with response frequency range. The occurrence of E. trivittatus significantly predicted narrower and asymmetric frequency-response curves in A. femoralis, without concomitant differences in the call or in body size. The number of acoustically coactive species did not significantly predict variation in any of the studied traits. Our results strongly support that the receiver but not the sender component of the communication system changed due to masking interference by a single species.     

Female Preferences for Call Traits and Male Mating Success in the Neotropical Frog Physalaemus enesefae

Female preferences for male call traits may affect male mating success and the evolution of exaggerated secondary sexual traits. We used phonotaxis experiments to examine female preferences in the frog Physalaemus enesefae in relation to variation in male call duration, dominant frequency, intercall interval and amplitude (dB SPL). Females preferred long calls, low and average dominant frequency calls, short intercall intervals and more intense calls. We compared the patterns of female preferences with those of acoustic variation among males to test the prediction that properties with low within‐male variation are associated with stabilizing or weakly directional female preferences, whereas properties with high within‐male variation are associated with directional preferences. Females had weakly directional preferences for the dominant frequency of the call and strongly directional preferences for call duration and call rate. We also determined whether the temporal relationship between calls influenced preferences based on the dominant frequency of the call. Preferences for low‐frequency over high‐frequency calls disappeared when calls partially overlapped. Females preferred the leading call regardless of its dominant frequency. We also investigated mating patterns in the field. There was size‐assortative mating, as male and female body sizes snout‐vent length (SVL) were positively correlated. In addition, differences in the frequency distributions of body length (SVL) between mated and unmated males approached significance; lower SVL classes were underrepresented among mated males. These patterns may reflect female preferences for lower dominant frequency calls, as there is a negative correlation between male mass and the dominant frequency of the call.     

Traffic noise differentially impacts call types in a Japanese treefrog (Buergeria japonica)

Acoustic noise from automobile traffic impedes communication between signaling animals. To overcome the acoustic interference imposed by anthropogenic noise, species across taxa adjust their signaling behavior to increase signal saliency. As most of the spectral energy of anthropogenic noise is concentrated at low acoustic frequencies, species with lower frequency signals are expected to be more affected. Thus, species with low-frequency signals are under stronger pressure to adjust their signaling behaviors to avoid auditory masking than species with higher frequency signals. Similarly, for a species with multiple types of signals that differ in spectral characteristics, different signal types are expected to be differentially masked. We investigate how the different call types of a Japanese stream breeding treefrog (Buergeria japonica) are affected by automobile traffic noise. Male B. japonica produce two call types that differ in their spectral elements, a Type I call with lower dominant frequency and a Type II call with higher dominant frequency. In response to acoustic playbacks of traffic noise, B. japonica reduced the duration of their Type I calls, but not Type II calls. In addition, B. japonica increased the call effort of their Type I calls and decreased the call effort of their Type II calls. This result contrasts with prior studies in other taxa, which suggest that signalers may switch to higher frequency signal types in response to traffic noise. Furthermore, the increase in Type I call effort was only a short-term response to noise, while reduced Type II call effort persisted after the playbacks had ended. Overall, such differential effects on signal types suggest that some social functions will be disrupted more than others. By considering the effects of anthropogenic noise across multiple signal types, these results provide a more in-depth understanding of the behavioral impacts of anthropogenic noise within a species.     

The function of three main call types in common cuckoo

Acoustic signals play a key role in shaping the relationships in birds. Common cuckoos Cuculus canorus are known to produce various call types, but the function of these calls has only been studied recently. Here, we used a combination of field recordings (conducted in 2017) and playback experiments (conducted in 2018) to investigate the functional significance of common cuckoo calls. We found significant differences in the characteristics between male two‐element “cu‐coo” and three‐element “cu‐cu‐coo” calls, with these two call types being used in different contexts. The three‐element male “cu‐cu‐coo” calls were associated with females emitting their “bubbling” call. Playback experiments revealed that both males and females exhibit stronger responses to playing female “bubbling” calls than with the calls of the Eurasian sparrowhawk (Accipter nisus) serving as a control, suggesting a significant intraspecific communication function for this call type. However, we did not find any evidence to support mate attraction in male calls, as females were not stimulated by playback of male calls compared with sparrowhawk calls in the control group.     

Acoustic Properties of Long Calls Given by Flanged Male Orang‐Utans (Pongo pygmaeus wurmbii) Reflect Both Individual Identity and Context

Long calls by flanged male Bornean orang‐utans (Pongo pygmaeus wurmbii) serve as a long‐distance communication signal in this semi‐solitary species and allow individuals to adjust their ranging behavior. Long calls can be heard up to circa 1 km in dense rainforest. Only flanged males emit them, in various contexts: spontaneously (where no disturbances from the environment are perceived by human observers), when highly aroused by another male’s long call or a falling tree nearby, or right after having pushed over a dead tree themselves. In this study, acoustic analyses of orang‐utan long calls at Tuanan in Central Kalimantan not only confirm the discrimination of individual males by their long calls but also demonstrate the discrimination of context based on the long calls’ acoustic structure, which is further supported by the females’ ranging responses according to long call contexts. Females with dependent offspring move away from spontaneous long call sources but appear to ignore long calls elicited by disturbance. Hence, Bornean orang‐utan females perceive measurable differences in acoustic characteristics of long calls given in different contexts. These findings concur with vocal discrimination of contexts in other non‐human primates.     

Vocal cooperation between the sexes in Little Spotted Kiwi Apteryx owenii

Sexual call dimorphism in birds is usually associated with sexual size dimorphism. Departures from this relationship can be used to infer call function, but research into inter‐sexual call differences, as with song function in general, has been restricted by a bias towards male passerines. The nocturnal and flightless New Zealand kiwi (Apterygidae) are acoustically similar but taxonomically and ecologically very different from other birds, so provide a contrast in exploring avian call function and evolution. However, kiwi acoustic ecology is poorly understood, with the calls of only one of the five kiwi species spectrally described, and acoustic differences between the sexes virtually unknown. We conducted the first bioacoustic study of Little Spotted Kiwi Apteryx owenii, and assessed sexual call dimorphism in this species. There were significant inter‐sexual differences in call temporal and frequency characteristics that were not related to size dimorphism. Contribution to duets and variation in temporal structure with call context also differed between the sexes. We suggest that these differences indicate divergent call function, with male calls more suited for territory defence, and female calls for pair contact. There was a striking lack of overlap in the frequency spectrum distributions of male and female calls, which was also unrelated to size and was further emphasized by the presence of formants in female calls. We propose that this provides evidence for inter‐sexual acoustic cooperation in call frequency, of a type which to our knowledge has not previously been described in birds. This may result from selection for enhanced joint resource defence in kiwi.     

The spectral structure of vocalizations match hearing sensitivity but imprecisely in Philautus odontotarsus

It is generally thought that for species using vocal communication the spectral properties of the sender’s calls should match the frequency sensitivity of the receiver’s auditory system. Nevertheless, few studies have investigated both sender and receiver characteristics in anuran species. In the present study, auditory brainstem responses (ABRs) were recorded in the serrate legged treefrog, Philautus odontotarsus, in order to determine if male call spectral structure and hearing sensitivity in males and females have co-evolved in this species. The results showed that the spectral structures of male vocalization match both male and female hearing sensitivity, even though the dominant frequencies of male calls (2.5 kHz) are mismatched with the regions of best frequency sensitivity (1.4 and 2.8 kHz). In addition, the results show that, in contrast with most previous ABR studies in non-human animals, but consistent with human studies, there are noticeable sex differences in peripheral auditory sensitivity in Philautus insofar as females exhibit lower auditory thresholds than males across the entire 1.8–18 kHz frequency range. The results also show that the dominant frequency of male calls is negatively correlated with body size, indicating that call characteristics reflect body size in this species which may be used by females during mate choice.     

Males’ calls carry information about individual identity and morphological characteristics of the caller in burrowing petrels

Acoustic communication in burrowing petrels has been poorly studied. However, as for many other bird species, acoustic communication seems to play an essential role in social interactions during the breeding season of these seabirds. Bachelor males call from their burrow, likely to attract females, but also when vocally challenged by other males. Calling in the breeding colony exposes petrels to high predation risks and thus it should provide an important benefit. The present study focuses on the informative content of males’ calls in the blue petrel Halobaena caerulea and the Antarctic prion Pachyptila desolata, two monogamous petrel species producing a single egg per year. We tested the hypotheses that acoustic parameters of a male's calls 1) reflect phenotypic characteristics, and 2) bear an individual vocal signature. To do so, we first tested on both species the relationships between seven morphometric measurements and 11 acoustic parameters using multivariate analyses. Second, we performed a between‐class analysis and calculated the potential of individuality coding (i.e. the ratio between intra‐ and inter‐individual variabilities) for acoustic parameters in both spectral and temporal domains. Results show acoustic parameters (especially energy quartiles, call duration, and syllable or phrase rate) reflect the caller's body size, bill morphology and wing morphology in both species. Considering the seeming pertinence of wing morphology, we suggest wing area may be a more relevant trait to consider than wing length when studying soaring birds. The results support the idea that energy quartiles, phrase rate and call duration also code for individual identity. Information carried by males’ calls might play a role in social interactions, such as burrow defence (e.g. male‐male competition, neighbour‐stranger discrimination) and/or female mate choice.     

Male–male interactions and male mating success in the leafhopper Aphrodes makarovi

In mating systems based on substrate‐borne vibrations, sexual communication often involves a reciprocal exchange of species‐ and sex‐specific vibrational signals and male is searching for a stationary female. In the leafhopper Aphrodes makarovi, female reply is essential for successful location of the female and its variable duration directly affects male's costs associated with signalling and searching. We studied male and female behaviour in a trio situation (two males and one female), and our results show that male–male competition had important effects on male mating success. Females replied equally to advertisement calls emitted by the winning and losing males and mated with the first male that located them, regardless of his investment in calling effort. Males eavesdropped to male–female duet maintained by the rival, and the winners were better at exploiting female replies to the rival's advertisement calls by silently approaching the female. To interfere with the ongoing male–female duet, males also emitted masking signals overlapping the latter part of the female reply. More overlapped female replies were registered in response to the losers and masking signals most likely delay the rival in reaching the female. Our study shows that a comprehensive understanding of male mating success and female preferences in vibrational duetting systems requires also investigations in more complex settings that more realistically represent the situation in nature.     

Arginine Vasotocin Injection Increases Probability of Calling in Cricket Frogs, but Causes Call Changes Characteristic of Less Aggressive Males

Male cricket frogs,Acris crepitanscommunicate to males and females using advertisement calls, which are arranged into call groups. Calls at the middle and end, but not beginning of the call group, are modified in response to male–male aggressive interactions. We found in this field study of male cricket frogs in natural breeding choruses that the peptide hormone arginine vasotocin (AVT) not only increased the probability that males called after injections, but also caused modifications in middle and end calls to produce calls characteristic of less aggressive males. Moreover, AVT-injected males showed significantly greater increases in call dominant frequency than saline-injected males, again, a characteristic of less aggressive males. Cricket frog calls are used to both repel males and attract females, thus call changes may relate to male–male and/or male–female interactions. Saline-injected males also demonstrated significant changes in several call traits, including changes that occurred in the beginning and middle calls of the call groups, but not the end calls. AVT appeared to block some call changes produced through handling. These data suggest that AVT can influence acoustic communication in frogs in several ways, including effects on call characteristics and dominant frequency, as well as potentially blocking some handling effects.     

Variation in Avian Vocalizations during the Non‐Breeding Season in Response to Traffic Noise

Low‐frequency traffic noise that leads to acoustic masking of vocalizations may cause birds to alter the frequencies or other components of their vocalizations in order to be heard by conspecifics and others. Altering parts of a vocalization may result in poorer vocal performance or the message contained in the vocalization being received incorrectly. During the winters of 2011–2012 and 2012–2013, we recorded and measured the ‘chick‐a‐dee’ call of Black‐capped Chickadees (Poecile atricapillus) and the ‘po‐ta‐to‐chip’ call of American Goldfinches (Spinus tristis) to determine whether components of the calls produced in areas of high traffic noise and low traffic noise differed in any way. We found that both chickadee and goldfinch calls had higher minimum frequencies in areas with high traffic‐noise than in low traffic‐noise areas. The maximum frequencies showed no differences in either species' calls. This suggests that chickadees and goldfinches alter the part of their calls that are acoustically masked by traffic noise in effort to better transmit the vocalization. These differences suggest that increasing anthropogenic noise may influence avian communication and that noise management should be included in conservation planning.     

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.     

Social Correlates of Variation in Male Calling Behavior in Blanchard's Cricket Frog,Acris crepitans blanchardi

I studied variation in male calling behavior and its social correlates in Blanchard's cricket frog, Acris crepitans blanchardi. Calls were produced in distinct call groups, and they increased in duration and complexity from the beginning to end of a call group. Dominant frequency was the only character of 18 quantified consistently correlated with male snout-vent length. Calls from the beginning of a call group varied independently of calls from the middle and end of a call group, and only calls from the beginning of a call group exhibited significant variation among males, thus relative consistency within males. Other characters varied greatly within individual males. Unlike most other anurans, dominant frequency also exhibited tremendous within-male variation. The relative influence of caller density, local caller density, nearest neighbor distance, and nearest neighbor sound pressure level on variation in male calling behavior was examined. Nearest neighbor distance, mediated through the sound-pressure level of neighbor calls, appeared to have the greatest influence on variation in male calling behavior. The most profound changes in calling behavior occurred during aggressive encounters; males altered their calling behavior in a manner suggesting that they respond to competitors with graded aggressive signals. Furthermore, the structure of the communication system suggests that calls are graded not only in response to the level of social competition, but graded over a call group as well.     

Female Preference Intensities on Different Call Characteristics and Symmetry of Preference Above and Below the Mean in the Iberian Midwife Toad Alytes cisternasii

The intensity of female preference for call characteristics is measured in two‐speaker playback tests with female Iberian midwife toads ‘Alytes cisternasii’ using an experimental design that allows quantitative comparisons across characters. Female preferences do not appear to be symmetrical above and below the population mean, female preference being more efficient at discriminating against low quality competing males that at selecting optimum males among good ones. Female preference is significantly more effective selecting males calling at higher call rates (a highly variable call characteristic probably related to the physical state of the male) rather than selecting calls of low dominant frequency (a characteristic of low intra‐individual variation, related to male size and age).     

Communication in a noisy environment: short-term acoustic adjustments and the underlying acoustic niche of a Neotropical stream-breeding frog

Acoustically active animals may show long- and short-term adaptations in acoustic traits for coping with ambient noise. Given the key role of calls in anurans’ life history, long- and short-term adaptations are expected in species inhabiting noisy habitats. However, to disentangle such adaptations is a difficult task, incipiently addressed for Neotropical frogs. We investigated if males of a stream-breeding frog (Crossodactylus schmidti) adjust call traits according to the background noise, and if the signal-to-noise ratio (SNR) varies between call harmonics and along call notes. We measured sound pressure levels of calls and noise in the field and used a fine-scale acoustic analysis to describe the signal and noise structure and test for noise-related call adjustments. The multi-note harmonic call of C. schmidti greatly varied in the spectral structure, including a trend for increasing note amplitude along the call, a wide frequency bandwidth of the 2nd harmonic, a minor call frequency modulation due to a trend for increasing note frequency within the same harmonic, and a major call frequency modulation due to the variable location of the dominant harmonic along the call. Calls had significantly higher frequencies than the noise at the range of the 1st and the 2nd call harmonics, and significantly louder sound pressure than the noise at the range of all harmonics. Males emitted the majority of call notes showing positive SNR, and though males also emitted some notes with negative SNR, when a given harmonic was negative the other harmonics in the same note did not tend to be SNR-negative. Our results indicate that male C. schmidti show short-term acoustic adjustments that make the advertisement call effective for coping with the interference of the stream-generated noise. We suggest that the call spectral plasticity serves for coping with temporary changes in the background noise, whilst we also discuss the possibility that the redundant, harmonic-structured call may have evolved to diminish masking interference on the acoustic signal by the background noise. This is the first study to uncouple noise-related acoustic adjustments and putative long-term acoustic adaptations for a Hylodidae, providing insights on behavioral plasticity and signal evolution of stream-breeding frogs.     

High‐throughput analysis of vocalizations reveals sex‐specific changes in Fmr1 mutant pups

There have been several reports that individuals with Fragile X syndrome (FXS) and animal models of FXS have communication deficits. The present study utilized two different call classification taxonomies to examine the sex‐specificity of ultrasonic vocalization (USV) production on postnatal day (PD8) in the FVB strain of Fmr1 knockout (KO) mice. One classification protocol requires the investigator to score each call by hand, while the other protocol uses an automated algorithm. Results using the hand‐scoring protocol indicated that male Fmr1 KO mice exhibited longer calls (P = .03) than wild types on PD8. Male KOs also produced fewer complex, composite, downward, short and two‐syllable call‐types, as well as more frequency steps and chevron call‐types. Female heterozygotes exhibited no significant changes in acoustic or temporal aspects of calls, yet showed significant changes in call‐type production proportions across two different classification taxonomies (P < .001). They exhibited increased production of harmonic and frequency steps calls, as well as fewer chevron, downward and short calls. According to the second high‐throughput analysis, female heterozygotes produced significantly fewer single‐type and more multiple‐type syllables, unlike male KOs that showed no changes in these aspects of syllable production. Finally, we correlated both scoring methods and found a high level of correlation between the two methods. These results contribute further knowledge of sex differences in USV calling behavior for Fmr1 heterozygote and KO mice and provide a foundation for the use of high‐throughput analysis of neonatal USVs.     

Breeding density affects the honesty of bird vocal displays as possible indicators of male/territory quality

Vocal displays are supposed to be an honest signal of the phenotypic and genetic quality of individuals and their territory. Moreover, signal interactions are nearly always associated with individuals in aggregations, and their function could in part be explained as social behaviour. Conspecific density has been shown to be a particularly strong proximate and ultimate factor acting on several individual/population features; thus, it may be expected to affect vocal behaviour too. Here, I investigate the hypothesis that, in long‐lived, territorial species, density affects the vocal displays of mated males, masking their honesty as a possible signal of male/territory quality. Each month I listened to the dusk calls of 17 breeding male Eurasian Eagle Owls Bubo bubo during their prelaying period. Nine males bred in a low‐density situation, the other eight in a high‐density one. Conspecific density was found to affect the honesty of call features as signals of male and/or territory quality. The call display as a reliable predictor of male fitness measured as productivity persisted only in situations of high breeding owl density, where male–male competition was stronger. Accommodation of call activity allows individuals to minimize the costs of aggressive calling by adjusting the territoriality threshold to local conditions. The results of this study emphasize the importance, when investigating the evolution and maintenance of honest territorial or sexual signals, of considering the environmental and social context experienced by the individual, thereby corroborating the idea that male–male competition contributes to the maintenance of honest signalling.     

INBREEDING AND ADVERTISEMENT CALLING IN THE CRICKET TELEOGRYLLUS COMMODUS: LABORATORY AND FIELD EXPERIMENTS

If sexually selected traits reveal a male's heterozygosity or condition to females, then such traits should exhibit declines with inbreeding. We tested this by examining the effect of inbreeding on advertisement calling in male crickets Teleogryllus commodus. We investigated the effect of one generation of full‐sibling mating on calling effort and fine‐scale call structure. Inbreeding reduced calling effort but had no effect on call structure. We then compared the attractiveness of inbred and outbred calls in the field by monitoring how many wild females were attracted to each call type. From the field data, we conducted a selection analysis to identify the major axes of linear and nonlinear multivariate sexual selection on call structure. A comparison of multivariate attractiveness of inbred and outbred calls along each major axis of selection revealed no difference in attractiveness. Our results suggest that inbred male calls have a fine‐scale structure that is no less attractive to females than that of outbred calls. However, because inbred males call less often, and female T. commodus prefer males with a higher calling effort, inbred males will suffer reductions in mating success. Females who base mate choice on call rate are therefore using a signal correlated with male heterozygosity and/or condition.