Repositório RCAAP

Vocal signals play a very important role in the life of both birds and echolocating bats, but these two unrelated groups of flying vertebrates have very different vocal systems. They nevertheless must solve many of the same problems in producing sound. This brief review examines avian and microchiropteran motor mechanisms for: 1) coordinating the timing of phonation with the vocal motor pattern that controls its acoustic properties, and 2) achieving respiratory strategies that provide adequate ventilation for pulmonary gas exchange, while also facilitating longer duration songs or trains of sonar pulses.

Many animals use complex communication calls in social behaviors. In some species we know the features in the calls that elicit particular behaviors, but we do not understand how the auditory system encodes the calls. Nor do we understand the mechanisms underlying neural selectivity to calls. Our studies of the auditory midbrain of the Moustached Bat Pteronotus parnellii have revealed a neural mechanism important for generating selective responses to calls. Neurons that integrate information across different frequencies show selectivity to communication calls. "Combination sensitivity" may be a common mechanism for encoding complex sounds because it is also important for encoding echolocation signals.

In the dense vegetation of temperate or tropical forests, communication processes are constrained by propagation-induced modifications of the transmitted sounds. The presence of leaves, trunks and branches induces important sound reverberation and absorption leading to diminution of the signal energy as well as qualitative modifications. The aim of this paper is to briefly review the different strategies used by birds to manage with these constraints. At the emitter's level, an adapted emission behavior which takes into account both the physical heterogeneities of the forest environment and the temporal variations of the acoustic constraints, is especially useful to control the active space of signaling. The coding of information into acoustic parameters that have different susceptibility to propagation constraints is also of great interest. At the receiver's level, an adaptive reception behavior (listening post) and a great tolerance to sound degradation during the decoding process are the keys to an optimal communication process.

The habitat, but also the nest hole of a hole-nesting species, will degrade the song during transmission. We investigated how the sounds degrade in a sound transmission experiment with the song of the Pied Flycatcher Ficedula hypoleuca (Muscicapidae). Ten different song elements were transmitted to microphones placed inside and outside a nest box. On average, song degradation was much greater inside than outside the nest boxes, especially with respect to excess attenuation and blurring of the song elements. Being inside a nest box therefore strongly reduces a Pied Flycatcher's possibility of detecting and recognizing songs or eavesdropping on singing interactions.

A bird needs to keep track not only of social interactions of conspecifics but also of their changing locations in space by determining their directions and distances. Current knowledge of accuracy in the computation of sound source location by birds is still insufficient, partly because physiological mechanisms of few species are studied in well defined laboratory settings, while field studies are performed in a variety of species and complex environments. Velocity gradients and reverberating surfaces may conceivably induce inaccuracy in sound source location (mainly elevation) by distorting the directional cues. However, most birds possess an inherently directional pressure difference receiver, which enhances the directional cues (mainly azimuth), and a computational mechanism in their auditory pathways to suppress echoes of redirected sound.

Most territorial songbirds live in communication networks where eavesdropping on vocal interactions may constitute an important option for gathering information regarding the relative dominance, condition and quality of individuals being eavesdropped upon. The relatively low costs and risks of eavesdropping, together with the obvious advantages of gaining such comparative information about other individuals, predict eavesdropping to be a widespread phenomenon even though it is not necessarily advantageous for the participants to be eavesdropped upon. Special eavesdropper strategies that facilitate eavesdropping (how best to eavesdrop) may therefore have evolved together with strategies for interacting that either co-facilitate (public signaling) or counter eavesdropping directly (private signaling) or indirectly by preventing any subsequent negative consequences of being eavesdropped upon (anonymity). This paper reviews the predictions for the strategies and also gives examples supporting their use by territorial songbirds in connection with vocal interactions.

Penguins identify their mate or chick by an acoustic signal, the display call. This identification is realized in a particularly constraining environment: the noisy world of a colony of thousands of birds. To fully understand how birds solve this problem of communication, we have done observations, acoustic analysis, propagation and playback experiments with 6 species of penguins studied in the field. According to our results, it appears that penguins use a particularly efficient ''anti-confusion'' and ''anti-noise'' coding system, allowing a quick identification and localization of individuals on the move in a noisy crowd.

Vocalizations with an emphasized fundamental are common in many species of animals. Such calls can presumably be sufficiently described by measures of their fundamental shape or 'contour'. Here we describe a software we developed to analyze such vocalizations semi-automatically. The software is particularly designed to cope with vocalizations recorded in a noisy environment. Some of the algorithms implemented (e.g. signal detection, contour detection, contour measurement, validation) and some preliminary applications dealing with calls of different species of birds are presented. Finally, we briefly discuss the possible significance of such vocalizations.

Vocal amplitude, one of the crucial factors for the exchange of acoustic signals, has been neglected in studies of animal communication, but recent studies on song variation in Common Nightingales Luscinia megarhynchos have revealed new insights into its importance in the singing behavior of territorial birds. In nightingales song amplitude is not maximized per se, but is individually regulated according to the level of masking background noise. Also, birds adjust their vocal intensity according to social variables, as in male-male interactions. Moreover, during such interactions, males exploited the directionality of their songs to broadcast them in the direction of the intended receivers ensuring the most effective signal transmission. Studies of the development of this typical long-range signaling suggest that sound level is highly interrelated with overall developmental progression and learning, and thus should be viewed as an integral part of song ontogeny. I conclude that song amplitude is a dynamic feature of the avian signal system, which is individually regulated according to the ecological demands of signal transmission and the social context of communication.

Evolution of dominant frequencies in songs of Eneopterinae crickets was studied with respect to phylogeny. Two characters are optimized on the tree: the first describes the frequency resulting from the vibration of the harp (Fda), and the second is due to the vibration of other tegminal areas (Fdb). Fda was found to be relatively stable through the subfamily. Its low ancestral state is replaced by a high Fda only once, resulting in high-frequency calling in [Cardiodactylus (Lebinthus-Agnotecous)]. A high Fdb component is added to the low ancestral Fda in Eneoptera guyanensis, resulting in frequency modulation. The onset of high Fd in this first subclade is accompanied by a high cladogenesis rate, which supports a hypothesis of adaptive radiation for high frequencies. The effectiveness of high-frequency calling is discussed in relation to the species behavior ecology.

Cricket stridulums and calls are highly stereotyped, except those with greatly modified tegmina and/or vena-tion, or ''unusual'' frequency, duration and/or intensity. This acoustic diversity remained unsuspected until recently, and current models of acoustic evolution in crickets erroneously consider this clade homogeneous for acoustic features. The few phylogenetic studies analyzing acoustic evolution in crickets demonstrated that acoustic behavior could be particularly labile in some clades. The ensuing pattern for cricket evolution is consequently extremely complex. We argue that: (1) phylogeny should always be considered when analyzing acoustic evolution, whatever characters are considered (signals, stridulums or behaviors). Consequently, future studies should be devoted to entire clades, and not consider isolated taxa; character and character state definitions should allow significant reconstructions of character evolutionary transformations; and homologies should be carefully defined for all characters, including behavior. (2) The factors responsible for song effectiveness should be reconsidered and hypotheses on their potential influence on signal evolution tested jointly by phylogenies (for example, to assess correlated transformations of acoustic and ecological features), and population studies (for example, to correlate call range and population structure, or test the predation risk associated with a signal structure). Better understanding these points should help clarifying acoustic evolution in crickets.

Recent bioacoustic investigations have shown that Cicadetta montana Scopoli 1772 is a complex of morphologically similar sister species that are best characterized by their song patterns. At the type locality of C. montana, only mountain cicadas with simple, long lasting song phrases were heard, recorded and collected. Therefore, we have good reasons to suggest that this type of song is characteristic for C. montana s. str. Boulard described a song of C. montana from France with phrases composed of a long and a short echeme; this type of song is characteristic for cicadas morphologically corresponding to C. montana var. brevipennis Fieber 1876; we suggest to raise this taxon to species level. On the basis of specific song, Puissant and Boulard described C. cerdaniensis from Pyrénées. A similar case was the discovery and description of C. montana macedonica Schedl 1999 from Macedonia; since these Macedonian cicadas are sympatric with at least two other cryptic species in the C. montana group and molecular investigations showed substantial genetic differences between C. macedonica and C. montana or C. brevipennis, we conclude that this taxon should also be raised to species level. Songs of closely related C. podolica and Korean mountain cicada are presented as well.

The song of the Blue-black Grassquit Volatinia jacarina is different for every individual and the structural differences between individuals are quite complex. Samples of songs from different Brazilian localities, as well as from Venezuela and Mexico, were studied through a comparative analysis of their sonograms. From the structural point of view, the results show a song composed of a single note that is compacted in a ''window'' between 2 and 13 kHz and rarely occupying more than half of a second. The note is essentially pure and is repeatedly uttered with a high level of fidelity. A global frequency modulation decreases from the beginning to the end of the song. The main song components are referred to as ''Blocks'' and are of three types: ''Vibrations'' (Buzzes or Vibratos), ''Arabesques'' (complex notes) and ''Isolated Modulations'' (simple syllables). Among other characteristics are double voices, which are quite diverse and probably function as codes for individual recognition. This song is considered a special case where a signature system has been developed to a high level of inter-individual variability.

The White-browed Warbler Basileuterus leucoblepharus, a common bird of the BrazilianAtlantic forest, emits only one distinct song type in the context of territorial defense. Individual or neighbor-stranger recognition may be more difficult when birds share similar songs. In fact, the analysis of songs of different individuals reveals slight differences in the temporal and the frequency domains. Effectively, a careful examination of the signals of different individuals (21) by 5 complementary methods of analysis reveals first, that one or two gaps in frequency occur between two successive notes at different moments of the song, and second, that their temporal and frequency positions are stereotyped for each individual. Playback experiments confirm these findings. By propagation experiments, we show that this individual information can be only transmitted at short range (< 100 m) in the forest. In regard to the size and the repartition of territories, this communication process appears efficient and adaptive.

The regional dialects or regiolects of the Rufous-collared Sparrow Zonotrichia capensis were compared between Campinas (47º06'W-22º90'S) and Botucatu (48º44'W-22º88'S), São Paulo State, Southeastern Brazil. Songs of 88 individuals from thirteen localities were recorded. Sonograms showed that two areas presented more homogeneous songs, forming two regiolects. In 11 localities most individuals shared the same song type. At the other two localities, they sang up to 5 different song types. This occurs at the boundaries of the regiolects, and was also where individuals singing more than one song type were found. Similarities between song types were not related to geographic distance between the respective singers. A comparative analysis showed similarities in these regiolects with song of populations from Northeastern Brazil.

This paper deals with acoustic communication in the Red-vented Bulbul Pycnonotus cafer. This species emits a high variety of vocal signals that can be classified on the basis of their acoustical features and context of production. Individuals sang throughout the year and most songs were discrete and stereotyped. The songs were composed of strophes (phrases) with minor structural variations of elements that were preceded and followed by a temporal gap (3 to 12s). Most strophes were composed of 2 to 6 elements that were often dissimilar in structure and ranging from 0.98 to 4.5 kHz. The biological function of the song appeared to be to maintain pair bonds and to synchronize breeding activities. Different types of context-specific calls were identified. Individuals produced Type-I alarm calls (fast and wide-band, 1.03 to 6.36 kHz) under low predation pressure andType-II calls (narrowfrequency range, 1.37 to 3.39 kHz) under high predation pressure. Roosting calls were fast and wide-band signals phonetically similar to Type-I alarm calls. Three types of begging/contact calls were recorded in nestlings/fledglings. Greeting calls and flight calls were composed of complex phrases, like song, but were short and used for proximate functions.

In the Budgerigar Melopsittacus undulatus, the significance of a conspecific alarm call was investigated in two seasons, winter and spring. Two qualitatively different behavioral responses were displayed by the receivers in reply to playbacks: call(s) and/or taking flight(s). The comparative analysis of the number of birds responding to the alarm and to the control signals revealed two major facts: 1) in both seasons, the responses to the alarm signal were only observed for females, not for males, 2) qualitatively, females exhibited a great inter-season variability in their behavioral responses to the hearing of an alarm call. In winter, the females were more predisposed to emit acoustic responses while in spring they mainly took flight.

The respective influence of testosterone and estradiol on the structure of the Common Canary Serinus canaria song was studied by experimentally controlling blood levels of steroid hormones in males and analyzing the consequent effects on acoustic parameters. A detailed acoustic analysis of the songs produced before and after hormonal manipulation revealed that testosterone and estradiol seem to control distinct song parameters independently. The presence of receptors for testosterone and estradiol in the brain neural pathway controlling song production strongly suggests that the observed effects are mediated by a steroid action at the neuronal level.

Guinea Pig Cavia porcellus pups emit high-pitched distress whistles when separated from their mother. In order to assess the influence of the duration of a brief isolation period on whistle acoustic structure, werecorded the distress whistles of six 8-day old pups separated for 15 min from their group in a novel environment and compared the mean values of the first and last 30 whistle notes. Acoustic analysis revealed, throughout the session, a significant decrease in whistle duration, an increase in mean frequency and a tendency for a decrease in number of harmonics in the first part of the note. Results demonstrate that, throughout a brief isolation period, the vocal response of Guinea Pig pups to isolation undergoes structural changes possibly related to time-dependent changes in motivational state.

The song of the Brazilian population of the Humpback Whale Megaptera novaeangliae was studied in its breeding and calving ground, the Abrolhos Bank, Bahia, Brazil, from July to November 2000. Aural and spectral analyses of digital recordings were completed for approximately 20 song cycles, totaling 5 hours of song from 10 different recording events. We identified 24 note types, organized in five themes. All songs presented the same themes and the order in which they were sung did not vary. We registered the appearance of a note type and the disappearance of a phrase ending, which indicate that the song changed as the season progressed. Moreover, we detected individual variation in the way singers performed certain complex note types. As songs are transmitted culturally, it is likely that singers have different abilities to compose and/or learn new notes. If, as it has been previously suggested, 'new' songs are preferred to 'old' ones, these more able singers will be sending out information about their learning abilities that could be used by other whales to decide whether or not to interact with them.