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Here we present an acoustic approach for reliable sexing in four whistling duck species from the genus Dendrocygna and compare it with molecular and cloacal  inspection techniques. In the four examined species, the White-faced Whistling Duck D. viduata, Fulvous Whistling Duck D. bicolor, Cuban Whistling Duck D. arborea and Red-billed Whistling Duck D. autumnalis, sexes are indistinguishable by appearance. However all  the four species show strong sexual differences in the structure of their species-specific loud whistles. For 59 examined birds, an acoustic-based sexing showed 100% accordance to the DNA PCR analysis, while the cloacal inspection showed only 89.8% accuracy. The results demonstrate that acoustic sexing represents a feasible alternative to the two traditional methods as a nonabrasive tool for the distant sexing of the four whistling duck species both in captivity and in the wild.

Australian fur seals are colonial breeding animals that give birth on crowded rookeries. Females leave their pups unattended for extended periods while they forage at sea. On return to the colony, a mother must relocate her pup amongst the hundreds of other pups. Vocal recognition is thought to play a vital role in maintaining the mother-pup bond. In the present study, four sets of 7 different pups were recorded once each at different times throughout the maternal dependence period. The Female Attraction Call was used to determine whether Australian fur seal pups produce individually distinct calls which could be used as a basis for vocal recognition. Results from three different analyses (PIC, DFA and CART) indicated that the fundamental frequency, number of parts per call, duration, quavering and peak frequency changes at the start, mid-point and end of the call (i.e., along PEAK F1) were important to recognition. In 75% of cases using DFA, the Female Attraction Call was classified to the correct caller, suggesting that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition by females.

We examined vocalisations of a solitary subterranean rodent, the Silvery Mole-rat Heliophobius argenteocinereus (Bathyergidae). Seven true vocalisations and one mechanical vocalisation were identified. The main frequencies of the analysed sounds (0.34-13.17 kHz) match to a great extent the frequency range suitable for transmission in underground burrows. Due to the narrow frequency range of vocalisations, motivation is predominantly expressed by the rate of tonality rather than by frequency changes.  The vocal repertoire of the Silvery Mole-rat perfectly matches to Morton's MS rules, i.e. that low-frequency and harsh vocalisations indicate hostility whereas high tonal calls signalize appeasement or fear. In comparison with social species, this solitary bathyergid produces fewer calls. It lacks contact and alarm calls, but has a rich repertoire of mating calls (mating ends with duet vocalization of male and female). Acoustic signals seem to play a major role in lowering natural aggressiveness during the mating period.

Research on African elephant (Loxodonta africana) vocal communication has increased in recent years, yet there has been very little data collected on the vocal production of infant African elephants. Vocalizations were recorded from a group of five adult female African elephants and 3 dependent offspring (1 male and 2 female) at Disney's Animal Kingdom, Florida, U.S.A., using custom-designed audio-recording collars worn by the adult females. We measured both source and filter features of infant ‘rumble’ vocalizations made during affiliative social interactions and after cessation of nursing from adult females. Rumble vocalizations produced in the ‘nurse cessation’ context exhibited an upward shift in formant frequency locations, compared to rumbles produced during the ‘affiliation’ context. Additionally, call duration increased and fundamental frequencies decreased after nurse cessations for the male, but both females showed the opposite acoustic response. When infant rumbles accompanied nurse cessations, nursing was more likely to resume within 30 seconds compared to nurse cessations without vocalizations. These results suggest that infant rumbles associated with cessation of nursing reflect the motivational state of infants and may influence maternal responsiveness.

We review Seewave, new software for analysing and synthesizing sounds. Seewave is free and works on a wide variety of operating systems as an extension of the R operating environment. Its current 67 functions allow the user to achieve time, amplitude and frequency analyses, to estimate quantitative differences between sounds, and to generate new sounds for playback experiments. Thanks to its implementation in the R environment, Seewave is fully modular. All functions can be combined for complex data acquisition and graphical output, they can be part of important scripts for batch processing and they can be modified ad libitum. New functions can also be written, making Seewave a truly open-source tool.  

Spectrograms visualise the time-frequency content of a signal. They are commonly used to analyse animal vocalisations. Here, we analyse how far we can deduce the mechanical origin of sound generation and modulation from the spectrogram. We investigate the relationship between simple mathematical events such as transients, harmonics, amplitude- and frequency modulation and the resulting structures in spectrograms. This approach yields not only convenient statistical description, but also aids in formulating hypotheses about the underlying mathematical mechanisms. We then discuss to what extent it is possible to invert our analysis and relate structures in spectrograms back to the underlying mathematical and mechanical events using two exemplary approaches: (a) we analyse the spectrogram of a vocalisation of the Bearded Vulture and postulate hypotheses on the mathematical origin of the signal. Furthermore, we synthesise the signal using the simple mathematical principles presented earlier; (b) we use a simple mechanical model to generate sounds and relate experimentally observed mechanical events to characteristics of the spectrogram. We conclude that although knowledge of sound producing systems increases the explanatory power of a spectrogram, a spectrogram per se cannot present unambiguous evidence about the underlying mechanical origin of the sound signal.

Here we present the first description of the vocal behaviour of the Tyrrhenian subspecies of Red Deer, the Corsican Deer. Vocalisations from calves, hinds and stags were recorded. Their acoustic characteristics were analysed in order to contrast these with published data characterising central European Red Deer hind and calve contact calls and Scottish Red Deer stag mating calls. We found that the vocal repertoire of Corsican Deer was very comparable with that of central European and Scottish Red Deer, with the exception of one call type, the harsh roar, absent in the Corsican Deer repertoire. Because Corsican Deer are the smallest subspecies of Red Deer, we expected calls to be characterised by higher spectral components. However, while male roars did have higher vocal tract resonances, consistent with a shorter vocal tract, we found that the fundamental frequency (F0) was much lower than predicted, in fact the lowest recorded in any studied Red Deer subspecies. We also found a strong sexual dimorphism in F0, with male calls approximately twice as low as female calls, suggesting that the low F0 observed in Corsican male roars is a result of sexual selection for lower-pitched males. The results of this study emphasise the phenotypic originality of Corsican Deer, and strengthen the case for its conservation. We also argue that future studies should compare the vocal behaviour of Corsican Deer with that of other circum-Mediterranean populations.