Exploring Sound Emission of the Lizard Pristidactylus valeriae.

Lizards, except geckos, are generally considered voiceless organisms, although some species emit oral sounds. For most of these "vocal lizards", however, there is almost no information on the characteristics of the sounds, precluding exploration of the functionality and evolution of the sounds. Pristidactylus are known as "grunter lizards" since individuals emit oral sounds under predation risk. We explored the characteristics of the sounds emitted by P. valeriae, recording 17 adults and 1 juvenile when they were threatened and captured by a predator. Only adults emitted sounds with open mouths and displayed aggressive postures, e.g., biting attempts. These sounds correspond to hisses, which lack amplitude or frequency modulation. The lizards emitted longer hisses when threatened than when captured by the predator, which may provide honest information on individuals' ability to escape. In addition, males may experience higher distress during threats since their hisses had higher aggregate entropy than those of the females. Finally, hissing has been documented in four of the five Leiosauridae genera, the family to which Pristidactylus belongs, suggesting that sound emission is ancestral to the family.

The distress context of social calls evokes a fear response in the bat Pipistrellus abramus.

Bats primarily use sound information, including echolocation, for social communication. Bats under stressful conditions, for example when confronted by a predator, will emit aggressive social calls. The presentation of aggressive social calls, including distress calls (DCs), is known to increase heart rate (fH), but how this change in fH is related to the bat's sound perception and how this evokes behaviors such as the fear response is unknown. Herein, we show that the perception of a distress context induces freezing behavior as a fear response in bats. We found that bats responded by freezing and displayed increased fH when they were presented with a conspecific donor bat in a distress situation evoked by gentle poking with a cotton swab. In addition, when we presented two types of auditory oddball paradigms with different probabilities of DCs and echolocation calls (ECs), the bats' fH increased when DCs were presented as deviant or control stimuli within standard ECs but did not increase when DCs were presented as standard stimuli. These results suggest that the situational context created by the frequency of sound presentation, rather than simply a single sound feature, induces fH increases and freezing as fear responses in bats.

Host parent responses to heterospecific parasite nestling alarm calls are independent of past and current experience with experimental brood parasitism.

Communication between parents and dependent offspring is critical not only during provisioning, but also in antipredator contexts. In altricial birds, a top cause of reproductive failure is nest predation, and alarm calls both by parents and chicks can serve to alert others and increase the likelihood of offspring escaping predation. Understanding the factors that determine the strength of parental antipredator responses to different nestling alarm calls can provide insight into parent-offspring recognition. The prothonotary warbler (Protonotaria citrea), a host of the obligate brood parasite, the brown-headed cowbird (Molothrus ater), never rejects cowbird young and raises the parasite together with its own offspring. To determine whether warbler parents learn cowbird nestling alarm calls, we presented experimentally parasitized or non-parasitized parents with playbacks of conspecific warbler, parasitic cowbird, and a harmless heterospecific control, eastern bluebird (Sialis sialis), nestling alarm calls. We recorded the latency to respond and the number of chips given by members of the resident warbler pair. We found that parents were most likely to respond to warbler nestling alarm calls, least likely to respond to bluebird calls, with a statistically intermediate likelihood of responding to cowbird calls. Critically, current and past parasitism status did not affect the likelihood of response to any playback or the number of chips given, however, currently parasitized parents had greater response latencies to playbacks than non-parasitized parents. These results suggest that warbler parents do not learn cowbird alarm calls from breeding experiences and, in turn, that cowbirds may employ a generalized, bet-hedging alarm call.

Comparing context-dependent call sequences employing machine learning methods: an indication of syntactic structure of greater horseshoe bats.

For analysis of vocal syntax, accurate classification of call sequence structures in different behavioural contexts is essential. However, an effective, intelligent program for classifying call sequences from numerous recorded sound files is still lacking. Here, we employed three machine learning algorithms (logistic regression, support vector machine and decision trees) to classify call sequences of social vocalizations of greater horseshoe bats (Rhinolophus ferrumequinum) in aggressive and distress contexts. The three machine learning algorithms obtained highly accurate classification rates (logistic regression 98%, support vector machine 97% and decision trees 96%). The algorithms also extracted three of the most important features for the classification: the transition between two adjacent syllables, the probability of occurrences of syllables in each position of a sequence, and the characteristics of a sequence. The results of statistical analysis also supported the classification of the algorithms. The study provides the first efficient method for data mining of call sequences and the possibility of linguistic parameters in animal communication. It suggests the presence of song-like syntax in the social vocalizations emitted within a non-breeding context in a bat species.

Vocal patterns of adult females and juveniles Caiman yacare (Crocodilia: Alligatoridae) in Brazilian Pantanal wetland / Patrones de vocalización de jóvenes y hembras adultas de Caiman yacare (Crocodilia: Alligatoridae) en el Pantanal de Brasil

The Paraguayan caiman (Caiman yacare) is the main Caimaninae species occurring in the Brazilian Pantanal Wetland. Despite the relative availability of works focused on biology and conservation of the Paraguayan caiman, almost nothing is known about its vocal structure and behavior. We recorded aggressive calls of adult caiman females guarding nests and, afterwards, the distress calls of the new born juvenile caimans in seasonally flooded areas of the Nhecolândia (Southern Pantanal). The results of both observations and sonographic analyses diverged from studies with other crocodilian species. Aggressive vocalization of adult females of the Paraguayan caiman was longer and more complex than the same vocalization of larger Alligatoridae species. Vocalizations of the young caimans presented interspecific differences with other crocodilian offsprings. Moreover, we found statistically significant intraspecific variation in the distress call structure among different pods, even separated by few kilometers. Differences in distress call structure were tested by Canonical Discriminant Analysis (CDA). We obtained the squared Mahalanobis distances between the acoustic multivariate spaces of each pod provided by the CDA and compared with the geographic distance between the bays of origin of each pod through Mantel Test. The geographic distance by itself did not explain the differences found in the structure of the vocalization of young caimans from different pods. The adult females of Paraguayan caiman positively responded to playbacks of calls from juvenile caimans from pods of other regions, as well as to rough imitations of distress call. Since the adult caimans showed protective responses to quite heterogeneous vocalizations of distress by juveniles, we hypothesized that the variation in the distress call pattern may be associated to a low specificity in sound recognition by adult caimans.

Poco se conoce sobre la estructura vocal del Caiman yacare del Pantanal brasileño. Llamadas agresivas de hembras adultas que cuidaban de los nidos fueron registradas durante enero y febrero y llamadas de socorro de caimanes jóvenes, en abril de 1992. Hembras adultas de C. yacare presentaron una vocalización agresiva más larga y compleja que en otras especies más grandes de Alligatoridae. Las vocalizaciones de los jóvenes caimanes también presentaron diferencias interespecíficas con otros cocodrilos y variaciones intraespecíficas entre grupos separados por pocos kilómetros. Se utilizó la Prueba de Mantel para comparar las distancias de Mahalanobis entre la estructura de las vocalizaciones de los jóvenes de acuerdo con sus grupos y las distancias geográficas donde ellos estaban. La distancia geográfica en sí no explica las diferencias en las vocalizaciones de jóvenes de diferentes grupos. Hembras adultas de C. yacare han respondido a grabaciones de llamadas de caimanes de grupos de otras regiones, así como a imitaciones de llamada de socorro. Se postula que las variaciones en las llamadas de socorro pueden estar asociadas con una baja especificidad en el reconocimiento de sonido por caimanes adultos que han respondido de la misma forma protectora a las más heterogéneas expresiones de peligro de los jóvenes.

Sound production and pectoral spine locking in a Neotropical catfish (Iheringichthys labrosus, Pimelodidae)

Catfishes may have two sonic organs: pectoral spines for stridulation and swimbladder drumming muscles. The aim of this study was to characterize the sound production of the catfish Iheringichthys labrosus. The I. labrosus male and female emits two different types of sounds: stridulatory sounds (655.8 + 230 Hz) consisting of a train of pulses, and drumming sounds (220 + 46 Hz), which are composed of single-pulse harmonic signals. Stridulatory sounds are emitted during abduction of the pectoral spine. At the base of the spine there is a dorsal process that bears a series of ridges on its latero-ventral surface, and by pressing the ridges against the groove (with an unspecialized rough surface) during a fin sweep, the animal produce a series of short pulses. Drumming sound is produced by an extrinsic sonic muscle, originated on a flat tendon of the transverse process of the fourth vertebra and inserted on the rostral and ventral surface of the swimbladder. The sounds emitted by both mechanisms are emitted in distress situation. Distress was induced by manipulating fish in a laboratory tank while sounds were recorded. Our results indicate that the catfish initially emits a stridulatory sound, which is followed by a drumming sound. Simultaneous production of stridulatory and drumming sounds was also observed. The catfish drumming sounds were lower in dominant frequency than stridulatory sounds, and also exhibited a small degree of dominant frequency modulation. Another behaviour observed in this catfish was the pectoral spine locking. This reaction was always observed before the distress sound production. Like other authors outline, our results suggest that in the catfish I. labrosus stridulatory and drumming sounds may function primarily as a distress call.

Bagres podem apresentar dois órgãos sonoros: o espinho peitoral para o som peitoral ou estridulatório e o músculo sonoro da bexiga natatória. O objetivo deste trabalho foi caracterizar a produção de som no bagre Iheringichthys labrosus. Essa espécie emite dois sons diferentes, o som peitoral ou estridulatório (655,8 + 230 Hz) que consiste numa série de pulsos, e o som de tamboril (220 + 46 Hz) que é composto por sinais harmônicos de pulso simples. O som peitoral é emitido com o movimento do espinho da nadadeira peitoral. A base do espinho possui um processo dorsal que suporta uma série de cristas na sua superfície lateroventral, e ao pressionar as cristas contra o sulco (com uma superfície rugosa não especializada) durante o movimento de abertura da nadadeira, se produz uma série de pulsos curtos. O som de tamboril é produzido por um músculo sônico extrínseco, originado em um tendão plano preso ao processo transversal da quarta vértebra e inserido nas superfícies rostral e ventral da bexiga natatória. Os sons são emitidos por ambos os mecanismos em situação de estresse, a qual foi induzida através da manipulação dos peixes em um tanque no laboratório, enquanto os sons eram gravados. Nossos resultados indicam que o bagre emite primeiro o som peitoral e em seguida o som de tamboril. Também foi observada a produção simultânea dos sons estridulatório e de tamboril. O som de tamboril mostra uma frequência dominante mais baixa do que o som peitoral, e também apresenta um grau menor de modulação de frequência dominante. Isso pode estar relacionado com um som de cortejo, como verificado em outros peixes teleósteos. Outro comportamento observado nessa espécie de bagre é a capacidade de travar o espinho peitoral. Essa reação foi observada imediatamente antes da produção do som. Como descrevem outros autores, nossos resultados sugerem que em I. labrosus o som de estridulação e de tamboril funcionam como uma chamada de alarme.