Conspecific Calls Research Articles

Sex differences in vocalization are reflected by event-related potential components in the music frog.

Sex differences in vocalization have been commonly found in vocal animals. It remains unclear, however, how animals perceive and discriminate these differences. The amplitudes and latencies of event-related potentials (ERP) components can reflect the auditory processing efficiency and time course. We investigated the neural mechanisms of auditory processing in the Emei music frog (Nidirana daunchina) using an Oddball paradigm with ERP. We recorded and analyzed eletroencephalogram (EEG) signals from the forebrain and midbrain when the subjects listened to white noise (WN) and conspecific sex-specific vocalizations. We found that (1) both amplitudes and latencies of some ERP components evoked by conspecific calls were significantly higher than those by WN, suggesting the music frogs can discriminate conspecific vocalizations from background noise; (2) both amplitudes and latencies of most ERP components evoked by female calls were significantly higher or longer than those by male calls, implying that the ERP components can reflect sex differences in vocalization; and (3) there were significant differences in ERP amplitudes between male and female subjects, suggesting a sexual dimorphism in auditory perception. Together, the present results indicate that the music frog could discriminate conspecific calls from noise, male's calls from female's ones, and sexual dimorphism of auditory perception existed in this species.

The association between evidence of a predator threat and responsiveness to alarm calls in Western Australian magpies (Cracticus tibicen dorsalis).

Alarm calls are a widespread form of antipredator defence and being alerted to the presence of predators by the alarm calls of conspecifics is considered one of the benefits of group living. However, while social information can allow an individual to gain additional information, it can also at times be inaccurate or irrelevant. Such variation in the accuracy of social information is predicted to select for receivers to discriminate between sources of social information. In this study, we used playback experiments to determine whether Western Australian magpies (Cracticus tibicen dorsalis) respond to the predator information associated with alarm calls. Magpies were exposed to the alarm calls of two group members that differed in the threat associated with the alarm call: one call was played in the presence of a predator model while the other was not—in order to establish differences in the predator information provided by each caller. We then played back the alarm calls of the same group members in the absence of the predator model to determine whether magpies responded differently to signallers in response to the previous association between the alarm call and a predator threat. We found that receivers showed significantly greater levels of responsiveness to signallers that previously gave alarm calls in the appropriate context. Thus, the accuracy of threat-based information influenced subsequent receiver response.

Multimodal stimuli regulate reproductive behavior and physiology in male túngara frogs

Unlike in terrestrial animals, the boundary between internal (e.g., hormones) and external (e.g., social) stimulation can be blurred for aquatic and amphibious species. When chemicals such as hormones and glandular secretions leach into the water, they can further interact with other signaling systems, creating multimodal stimuli. It is unclear, however, whether water-borne chemical secretions from courting male frogs affect the physiology and behavior of their rivals. In order to address this question we first established non-invasive, continuous sampling methods for simultaneously measuring both hormones and behavior in amphibious species. Then, we examined whether interactions between water-borne chemical secretions and conspecific calls affect reproductive behavior and physiology (testosterone and corticosterone) of courting male túngara frogs. Our results demonstrate that conspecific acoustic stimulation alone increases locomotor activity, decreases latency to call, and increases calling behavior but does not alter the amount of hormones excreted. In response to water containing chemical secretions from rivals, but in the absence of calls from other males, males excrete more testosterone. Interestingly, the combined acoustic and chemical stimulus causes a multiplicative increase in both calling behavior and hormonal excretion. Taken together, our results suggest that a multimodal chemical-acoustic stimulus physiologically primes males for aggressive behavior.

Whispers on the wind: male cane toads modify mate searching and amplexus tactics based on calls from other males

In many species of anurans, males produce advertisement calls that function to attract reproductively active females. Rival males may use the public information in these calls to optimize their own tactics for acquiring mates. To see whether male cane toads, Rhinella marina, modify their mate-searching and amplexus behaviours in response to conspecific calls, we monitored toads in outdoor enclosures while playing recordings of advertisement calls, a biologically irrelevant stimulus with similar acoustic properties or silence. Male toads were seven times more likely to engage in amplexus and moved twice as much during a toad chorus than during the control sound or silence. Nonacoustic cues also influenced propensity to initiate amplexus, with males five to 16 times more likely to amplect a moving target than a stationary one (regardless of the sex of the animal being amplexed). Our study shows that male toads dramatically alter their behaviour in response to acoustic and visual information from conspecifics, suggesting that this public information holds substantial value to them as they seek to fine-tune their own reproductive tactics.

MEMRI for visualizing brain activity after auditory stimulation in frogs.

Anuran amphibians are common model organisms in bioacoustics and neurobiology. To date, however, most available methods for studying auditory processing in frogs are highly invasive and thus do not allow for longitudinal study designs, nor do they provide a global view of the brain, which substantially limits the questions that can be addressed. The goal of this study was to identify areas in the frog brain that are responsible for auditory processing using in vivo manganese-enhanced MRI (MEMRI). We were interested in determining if the neural processing of socially relevant acoustic stimuli (e.g., species-specific calls) engages a specific pattern of brain activation that differs from patterns elicited by less- or nonrelevant acoustic signals. We thus designed an experiment, in which we presented three different types of acoustic stimuli (species-specific calls, band-limited noise, or silence) to fully awake northern leopard frogs (Rana pipiens) and then conducted MEMRI T1-weighted imaging to investigate differences in signal intensity due to manganese uptake as an indication of brain activity across all three conditions. We found the greatest change in signal intensity within the torus semicircularis (the principal central auditory region), the habenula, and the paraphysis of frogs that had been exposed to conspecific calls compared with noise or silence conditions. Stimulation with noise did not result in the same activation patterns, indicating that signals with contrasting social relevance are differentially processed in these areas of the amphibian brain. MEMRI provides a powerful approach to studying brain activity with high spatial resolution in frogs. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Diverse patterns of temporal selectivity in the evoked vocal responses of a frog from the temperate austral forest, Batrachyla taeniata (Batrachylidae)

ABSTRACT Evoked vocal responses of male frogs Batrachyla taeniata to synthetic advertisement calls and variants having different temporal features altered parametrically were studied to identify patterns of evoked vocal responses (EVRs) that conform with static and dynamic modes of variation and with corresponding selective processes affected by different temporal components of the acoustic signals. Frogs responded with higher call rates and longer call durations to stimuli of 25–100 pulses/s, resembling conspecific calls. This response mode was not related to spectral differences among stimuli, as frogs responded similarly to a series of stimuli built with noise instead of tones. Frogs responded with lower call rates and shorter call durations to a non-pulsed 500-ms tone having the duration of the complete call, a decrement related to the dissimilar spectral composition of the tone, restricted to a single frequency, as frogs responded strongly to a non-pulsed 500-ms stimulus built with noise instead of a 2.1-kHz sinusoidal. Frogs responded with lower call rates and shorter call durations to synthetic calls composed by 3 or less pulses. The EVRs for pulse rate stimuli series are consistent with a stabilizing selectivity pattern, whereas EVRs for pulse duration and call duration stimuli series conform with directional selectivity patterns.

A broad filter between call frequency and peripheral auditory sensitivity in northern grasshopper mice (Onychomys leucogaster).

Acoustic communication is a fundamental component of mate and competitor recognition in a variety of taxa and requires animals to detect and differentiate among acoustic stimuli (Bradbury and Vehrencamp in Principles of animal communication, 2nd edn., Sinauer Associates, Sunderland, 2011). The matched filter hypothesis predicts a correspondence between peripheral auditory tuning of receivers and properties of species-specific acoustic signals, but few studies have assessed this relationship in rodents. We recorded vocalizations and measured auditory brainstem responses (ABRs) in northern grasshopper mice (Onychomys leucogaster), a species that produces long-distance calls to advertise their presence to rivals and potential mates. ABR data indicate the highest sensitivity (28.33 ± 9.07dB SPL re: 20μPa) at 10kHz, roughly corresponding to the fundamental frequency (11.6 ± 0.63kHz) of long-distance calls produced by conspecifics. However, the frequency range of peripheral auditory sensitivity was broad (8-24kHz), indicating the potential to detect both the harmonics of conspecific calls and vocalizations of sympatric heterospecifics. Our findings provide support for the matched filter hypothesis extended to include other ecologically relevant stimuli. Our study contributes important baseline information about the sensory ecology of a unique rodent to the study of sound perception.

Ecological Determinants of Species Richness and Abundance of Endemic and Threatened Owls in the Andaman Islands, India

Factors that influence the distribution and abundance of the endemic and threatened owls of the Andaman Islands have not been assessed, in contrast to those affecting diurnal birds. Such studies would assist in prioritising habitats that have high conservation importance for owls. We evaluated the status and species composition of owls along c. 343km of the Andaman Trunk Road, employing one-time point counts between December 2013 and April 2015. We conducted spontaneous listening, broadcasting of conspecific calls and spotlight searches as survey protocols. The pointcentred quarter method was used to evaluate the habitat at each count site. We recorded five owl species whose mean abundance was 2.09 owls/point. Species richness and abundance were greater in unlogged sites and deciduous forests. Habitat differences between owl species were noted according to land use, cover type and intensity of logging activity. However, these factors had no significant effect on the abundance of Oriental Scops-owl and Hume's Boobook, but were significant for Andaman Boobook and Andaman Scops-owl. Mean understory height, tree height and grass cover positively influenced the owl species richness and abundance. The Andaman Boobook and Andaman Scops-owl appeared stenotopic in habitat use and in contrast to the eurytopic Oriental Scops-owl and Hume's Boobook. A review of the conservation status of Andaman Scops-owl and Andaman Boobook is suggested bearing in mind their low abundance, restricted distribution and less preference for altered habitats.–Babu, S., Sureshmarimuthu, S. & Kumara, H.N. (2019). Ecological determinants of species richness and abundance of endemic and threatened owls in the Andaman Islands, India.Ardeola, 66: 89-100.

Social scavenging by wintering striated caracaras (Phalcoboenus australis) in the Falkland Islands

Avian scavengers perform vital ecosystem services by removing waste and slowing disease, yet few details are known about the process of carcass depletion, or the role of social interactions among groups of scavengers. The striated caracara (Phalcoboenus australis) is a social scavenging falconid of the Falkland Islands, whose boldness and reliance on human settlements as winter foraging grounds make it an ideal species with which to closely examine carcass use over the entire period of a carcass’ availability. By providing and monitoring experimental carcasses, we estimated the mass of food consumed per individual during 5-min intervals and compared the rate of group formation in the presence and absence of conspecific vocalizations. We found (1) that food obtained per individual was greater toward the beginning of carcass availability, when competition was fierce; (2) that vocalizations, by birds at and approaching the carcass, preceded periods of faster group formation; and (3) that on average birds would approach a speaker playing conspecific calls more closely than one playing a control recording. Our observations add to those of social foraging in other scavengers, providing a study of carcass use and vocalization at these ephemeral resources. Currently ranked as Near Threatened by BirdLife International, the remote and restricted range of the striated caracara (Phalcoboenus australis) has made it a difficult study subject, though conservation concerns show it warrants deeper research. A social scavenging falconid of the Falkland Islands, striated caracaras have been persecuted as livestock pests since the 1800s, but their reliance on human settlements as winter foraging grounds makes them an ideal species with which to examine social scavenging behavior. This study was undertaken to investigate group feeding at carcasses by striated caracaras in austral winter, and to better understand the social function of their vocalizations. Furthering our knowledge of avian vocalizations is essential to certain wildlife management strategies, and empirically testing the effects of playbacks on target species is a crucial prior step to the use of any bio-acoustic tool.

Effects of ambient noise on zebra finch vigilance and foraging efficiency.

Ambient noise can affect the availability of acoustic information to animals, altering both foraging and vigilance behaviour. Using captive zebra finches Taeniopygia guttata, we examined the effect of ambient broadband noise on foraging decisions. Birds were given a choice between foraging in a quiet area where conspecific calls could be heard or a noisy area where these calls would be masked. Birds foraging in noisy areas spent a significantly more time vigilant than those in quiet areas, resulting in less efficient foraging. Despite this there was no significant difference in the amount of time spent in the two noise regimes. However there did appear a preference for initially choosing quiet patches during individuals’ second trial. These results emphasise how masking noise can influence the foraging and anti-predation behaviour of animals, which is particularly relevant as anthropogenic noise becomes increasingly prevalent in the natural world.

Timing of the advertisement call of the common tink frog (Diasporus diastema) shifts with the acoustic behaviour of local conspecifics

ABSTRACTWe investigated the temporal dynamics of acoustically interacting common tink frogs (Diasporus diastema), a species in which advertising males maintain large inter-individual distances that may influence call timing behaviours among nearest neighbours. This species produces advertisement calls in temporally structured bouts, with decreasing inter-note intervals that culminate in a ‘burst’ sequence of rapidly emitted notes. We broadcast playbacks of unaltered and temporally manipulated conspecific advertisement calls to focal male individuals vocalizing within triads (comprised of closely neighbouring focal and non-focal males and a more distant, outsider male). Focal males demonstrated rhythmic entrainment and adjusted their calling behaviour to overlap their call sequences with those of their nearest vocalizing neighbour, including the unaltered conspecific playback. When presented with a playback of conspecific calls lacking the natural temporal sequence, focal males reduced the duration of the silent interval between call bouts and reduced the number of notes in the burst phase of their call bout, indicating the significance of the multi-element temporally complex call bout structure in mediating male–male vocal interactions.

Auditory perception exhibits sexual dimorphism and left telencephalic dominance in Xenopus laevis.

ABSTRACTSex differences in both vocalization and auditory processing have been commonly found in vocal animals, although the underlying neural mechanisms associated with sexual dimorphism of auditory processing are not well understood. In this study we investigated whether auditory perception exhibits sexual dimorphism in Xenopus laevis. To do this we measured event-related potentials (ERPs) evoked by white noise (WN) and conspecific calls in the telencephalon, diencephalon and mesencephalon respectively. Results showed that (1) the N1 amplitudes evoked in the right telencephalon and right diencephalon of males by WN are significantly different from those evoked in females; (2) in males the N1 amplitudes evoked by conspecific calls are significantly different from those evoked by WN; (3) in females the N1 amplitude for the left mesencephalon was significantly lower than for other brain areas, while the P2 and P3 amplitudes for the right mesencephalon were the smallest; in contrast these amplitudes for the left mesencephalon were the smallest in males. These results suggest auditory perception is sexually dimorphic. Moreover, the amplitude of each ERP component (N1, P2 and P3) for the left telencephalon was the largest in females and/or males, suggesting that left telencephalic dominance exists for auditory perception in Xenopus.

The effects of anthropogenic noise on feeding behaviour in black-capped chickadees (Poecile atricapillus)

Anthropogenic noise has been shown to impact animal behaviour. Most studies investigating anthropogenic noise, and the detrimental effect it has on behaviour, have been conducted in the field, where a myriad of covariates can make interpretation challenging. In this experiment, we studied the effects of an approximation of anthropogenic noise, simulated with brown noise, on the feeding behaviour of wild-caught black-capped chickadees in a laboratory setting. We measured the amount of time spent eating while subjects heard either conspecific calls, brown noise, or a combination of calls and brown noise. We found that subjects fed more in the silence following playback than during the playback itself for all types of stimuli, suggesting that chickadees may shift their feeding behaviour to avoid feeding during periods of noise. The ability to adapt to changing environments (e.g., varying noise levels) may allow species to thrive in the presence of anthropogenic noise. Our findings outline a laboratory-based method that could be adopted and adapted to examine a variety avian species and of types anthropogenic noise.

Influence of conspecific and heterospecific cues on phonotaxis behavior in a polyandrous treefrog

Although a large proportion of the literature has addressed the direction and preference of female choice in frogs, research about how males locate a breeding site and what strategies are involved in aggregation has been much less explored. By using broadcasting tests on a polyandrous choral treefrog Rhacophorus prasinatus, we examined how male frogs use conspecific and heterospecific signals to locate a chorus by asking the following questions: (1) Do male frogs prefer to join a large or a small chorus? (2) Do male frogs prefer to approach a high-quality or a low-quality male? (3) Do males utilize heterospecific calls to locate the potential breeding sites? (4) Do male frogs orient toward or avoid choruses containing heterospecific calls? Our results indicated that males prefer to join a large rather than small chorus. Low-quality males tend to approach high-quality males, which might be explained as the sneaking behavior of satellite males. Furthermore, males may use heterospecific calls delivered by a noncompetitive sympatric species (a ranid frog) to find potential breeding sites, but not by a sympatric competitor (another rhacophorid frog) that occupies a similar niche. Although the males did not show significant preference between conspecific chorus and mixed-specific chorus in the broadcasting tests, recapture records in the wild indicated that a high ratio of males would leave the mixed-specific choruses and move toward conspecific choruses in the next capture event. Although a large proportion of the literature has addressed the direction and preference of female choice in frogs, research about how males locate a breeding site and what strategies are involved in aggregation has been much less explored. Our study represents one of the first to test the orientation of males during breeding season, when the spatial scale in the experimental design is comparable to the real situation in the wild. Our results supported the prediction that both conspecific and heterospecific cues are used as information for males to assess the quality of breeding sites. Heterospecific calls may play dual functions for the males, which might become interference when coexisting with conspecific calls but may also provide cues for a potential habitat when conspecific calls are absent.

Heterospecific recognition of referential alarm calls in two species of lemur

ABSTRACTAlarm vocalizations are a common feature of the mammalian antipredator response. The meaning and function of these calls vary between species, with some species using calls to reference-specific categories of predators. Species can also use more than just the calls of conspecifics to detect threat, ‘eavesdropping’ on other species’ signalling to avoid predation. However, the evidence to date for both referential signalling and eavesdropping within primates is limited. We investigated two sympatric populations of wild lemur, the Coquerel’s sifaka Propithecus coquereli and the common brown lemur Eulemur fulvus, presenting them with playbacks of predator calls, conspecific alarm calls and heterospecific lemur alarm calls, and recorded their behavioural responses following the playbacks. Results suggest that the Coquerel’s sifaka may have functionally referential alarm calls with high specificity for aerial predators, but there was no evidence for any referential nature of the other call investigated. Brown lemurs appear to have a mixed alarm system, with one call being specific with respect to aerial predators. The other call investigated appeared to reference terrestrial predators. However, it was also used in other contexts, so does not meet the criteria for functional reference. Both species showed evidence for heterospecific alarm call recognition, with both the Coquerel’s sifaka and the brown lemurs responding appropriately to heterospecific aerial alarm calls.

Decoding the ‘zeep’ complex: quantitative analysis of interspecific variation in the nocturnal flight calls of nine wood warbler species (Parulidae spp.)

ABSTRACTThe “zeep” complex consists of nine birds that produce nocturnal flight calls with similar acoustic features. Our inability to distinguish these calls inhibits the acoustic monitoring of these species. We test the hypothesis that flight calls of nine warblers in the “zeep” complex show sufficient acoustic differences to allow differentiation. We investigate divergence in these vocalizations by recording birds held for banding and collecting additional recordings from sound libraries. We used three approaches to compare calls between species: analysis of variance in acoustic properties, discriminant analysis of acoustic properties, and spectrographic cross-correlation. The first approach revealed five species that were different in one or more acoustic properties. The second approach revealed a level of assignment to the correct species (73%) that exceeded levels expected by chance (36%). The third approach revealed calls of seven species to be significantly more similar to conspecific calls than heterospecific calls. Our results suggest the calls of many members of the “zeep” complex exhibit species-specific differences in structure, which may allow differentiation of at least five “zeep” species based on call alone. We advocate for the combined use of these three approaches for the comparison of “zeep” calls in future flight call studies.

Multiple adaptive and non-adaptive processes determine responsiveness to heterospecific alarm calls in African savannah herbivores.

Heterospecific alarm calls may provide crucial survival benefits shaping animal behaviour. Multispecies studies can disentangle the relative importance of the various processes determining these benefits, but previous studies have included too few species for alternative hypotheses to be tested quantitatively in a comprehensive analysis. In a community-wide study of African savannah herbivores, we here, for the first time to our knowledge, partition alarm responses according to distinct aspects of the signaller–receiver relationship and thereby uncover the impact of several concurrent adaptive and non-adaptive processes. Stronger responses were found to callers who were vulnerable to similar predators and who were more consistent in denoting the presence of predators of the receiver. Moreover, alarm calls resembling those of conspecifics elicited stronger responses, pointing to sensory constraints, and increased responsiveness to more abundant callers indicated a role of learning. Finally, responses were stronger in risky environments. Our findings suggest that mammals can respond adaptively to variation in the information provided by heterospecific callers but within the constraints imposed by a sensory bias towards conspecific calls and reduced learning of less familiar calls. The study thereby provides new insights central to understanding the ecological consequences of interspecific communication networks in natural communities.

Ravens adjust their antipredatory responses to con‐ and hetero‐specific alarms to the perceived threat

AbstractHeterospecific alarm calls are typically found in situations where multiple species have a common predator. In birds, they are particularly common in mixed mixed‐species flocks. In species with highly developed social and cognitive abilities like corvids, there is the potential for differential responses to heterospecific vs. conspecific calls according to the riskiness of the habitat. We tested the responses of free‐ranging ravens (Corvus corax) to conspecific alarm calls and compared them to heterospecific alarm calls of jackdaws (Corvus monedula). We observed the proportion of ravens leaving the feeding site after the con‐ or hetero‐specific playback was presented in a situation of low threat (wild boar—Sus scrofa enclosure) and high threat of predation (wolf—Canis lupus enclosure). We show that ravens responded to conspecific calls more intensively at the wolves than at the wild boar, but the response to conspecific calls was in both enclosures stronger than to the control (great tit—Parus major song). The response to the heterospecific alarm was also stronger in the wolves’ enclosure, but it did not differ from control in the wild boar enclosure. These findings suggest that ravens are aware of the meaning of the jackdaw alarm calls, but they respond to it only in a situation of high predatory threat (wolves are present). In the wild boar enclosure, the ravens probably consider jackdaws warning against some other predator, very probably harmless to ravens. This interpretation requires further testing, as both enclosures differ also in respect to other parameters like food quality and shelter availability.

Selective reactions to different killer whale call categories in two delphinid species.

The risk of predation is often invoked as an important factor influencing the evolution of social organization in cetaceans, but little direct information is available about how these aquatic mammals respond to predators or other perceived threats. We used controlled playback experiments to examine the behavioral responses of short-finned pilot whales (Globicephala macrorhynchus) off Cape Hatteras, NC, USA, and Risso's dolphins (Grampus griseus) off the coast of Southern California, USA, to the calls of a potential predator, mammal-eating killer whales. We transmitted calls of mammal-eating killer whales, conspecifics and baleen whales to 10 pilot whales and four Risso's dolphins equipped with multi-sensor archival acoustic recording tags (DTAGs). Only playbacks of killer whale calls resulted in significant changes in tagged animal heading. The strong responses observed in both species occurred only following exposure to a subset of killer whale calls, all of which contained multiple non-linear properties. This finding suggests that these structural features of killer whale calls convey information about predatory risk to pilot whales and Risso's dolphins. The observed responses differed between the two species; pilot whales approached the sound source while Risso's dolphins fled following playbacks. These divergent responses likely reflect differences in anti-predator response mediated by the social structure of the two species.

Brain Activation Patterns in Response to Conspecific and Heterospecific Social Acoustic Signals in Female Plainfin Midshipman Fish, Porichthys notatus

While the peripheral auditory system of fish has been well studied, less is known about how the fish’s brain and central auditory system process complex social acoustic signals. The plainfin midshipman fish, Porichthys notatus, has become a good species for investigating the neural basis of acoustic communication because the production and reception of acoustic signals is paramount for this species’ reproductive success. Nesting males produce long-duration advertisement calls that females detect and localize among the noise in the intertidal zone to successfully find mates and spawn. How female midshipman are able to discriminate male advertisement calls from environmental noise and other acoustic stimuli is unknown. Using the immediate early gene product cFos as a marker for neural activity, we quantified neural activation of the ascending auditory pathway in female midshipman exposed to conspecific advertisement calls, heterospecific white seabass calls, or ambient environment noise. We hypothesized that auditory hindbrain nuclei would be activated by general acoustic stimuli (ambient noise and other biotic acoustic stimuli) whereas auditory neurons in the midbrain and forebrain would be selectively activated by conspecific advertisement calls. We show that neural activation in two regions of the auditory hindbrain, i.e., the rostral intermediate division of the descending octaval nucleus and the ventral division of the secondary octaval nucleus, did not differ via cFos immunoreactive (cFos-ir) activity when exposed to different acoustic stimuli. In contrast, female midshipman exposed to conspecific advertisement calls showed greater cFos-ir in the nucleus centralis of the midbrain torus semicircularis compared to fish exposed only to ambient noise. No difference in cFos-ir was observed in the torus semicircularis of animals exposed to conspecific versus heterospecific calls. However, cFos-ir was greater in two forebrain structures that receive auditory input, i.e., the central posterior nucleus of the thalamus and the anterior tuberal hypothalamus, when exposed to conspecific calls versus either ambient noise or heterospecific calls. Our results suggest that higher-order neurons in the female midshipman midbrain torus semicircularis, thalamic central posterior nucleus, and hypothalamic anterior tuberal nucleus may be necessary for the discrimination of complex social acoustic signals. Furthermore, neurons in the central posterior and anterior tuberal nuclei are differentially activated by exposure to conspecific versus other acoustic stimuli.