birds

Measures of six temporal relations in the pigeon's courtship songs from four individual males which differed in age and courtship experience were taken. Intra- and interindividual variation was studied. Individual long term vocal stability is especially found in the whole length of the strophe, the length of the "trill'' phrase and the length of the "coo".

In this paper we document the pattern of geographic variation in song of the Corn Bunting in a marked population in Sussex. Song variation is best described as a system of local dialects with three song types in each dialect. We examine the inheritance of dialects from father to son; sons sing the same dialect as their nearest neighbour, rather than inheriting the dialect of the father. Therefore songs seem to relearned after dispersal. We also compare the dialects of mates and fathers of females; our results suggest that females do not rely on dialects when pairing. These results are discussed in the context of the current controversy surrounding other species with dialects and hypotheses relating dialects to the genetic structure of populations.

Observations made on the behaviour and sound recordings made of the calls chiefly in the early part of the breeding season in the South Ukraine indicate that the Great Black-headed Gull Larus ichthyaetus has a limited vocal repertoire, producing only eight different types of call associated with various behavioural contexts. Sonagraphic analysis of these sounds shows that their harmonic structure is confused, like that of the calls of L. melanocephalus and L. relictus and unlike the stronger harmonic organization of the calls of L.argentatus, L fuscus and L. marinus. Furthermore, there is no signal warning of approaching danger. This acoustic evidence supports the theory that L. ichthyaetus is more closely related to L. relictus and other ''primitive hooded'' gulls than to L. argentatus and other ''large white-headed'' gulls of the genus.

Incomplete song strophes in free-living territorial Chaffinch males can be induced by different experimental as well as natural stimulus situations including replay of species-specific song, approaching of human beings, and aggressive encounters with con-specific males. While the first post-stimulus song strophe is shortest the following ones gradually attain their full number of elements again. The strength of this reaction differs with regard to different stimuli.

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.

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.

Nestling begging behaviour has long been seen as a signal by which nestlings solicit care from parents and most of the existing evidence provides some support for it being an honest signal. Begging is a multicomponent signal in which both sound and vision components are usually important. Although it is known that begging encodes information about nestling hunger the present knowledge about the specific behavioural features that convey the information is still scarce. The aim of this study was to describe begging calls of Iberian Azure-winged Magpie Cyanopica (cyana) cooki nestlings and examine how information on nestling hunger might be encoded in the begging calls. Nestlings were experimentally submitted to different periods of food deprivation and the call variation within individuals was studied. The young were individually tested and stimulated to beg by simulating parental visits. When subject to increasing food deprivation periods, nestlings increased the response level to simulated parental visits. The study also found that for the studied size differences, nestlings did not differ in their response level. Results confirmed that information on nestlings’ hunger might be encoded in parameters of the calling behaviour. When the food deprivation periods increased, nestlings tended to start begging earlier, begged more often, extended their calling bout and increased the call duration, changing both at the level of the call and vocal begging bout. Overall the results support the view of begging as an honest signal, namely that begging should reflect nestling hunger and that only some call features might encode information about hunger.

Methods normally used for acoustic individual identification can only compare a single song type, both within and between individuals, to determine identity, i.e. they are call-dependent. Call-independent identification does not involve direct comparison of a particular song type. It can therefore be carried out regardless of the amount of song sharing between individuals, or changes in an individual’s repertoire over time. This wide applicability radically expands the range of situations in which acoustic individual identification can be used. Text-independent recognition is routinely conducted on human speech and in this paper the same techniques, using mel-frequency cepstral coefficients and multilayer perceptrons, were applied to bird song. Call-independent identification accuracies ranged from 54.3-75.7% in three passerine species. To suit bird song better, we modified the feature extraction methods and neural network architecture, resulting in accuracies of 69.3-97.1%. A comparison of call-dependent and call-independent identification showed little difference in accuracy for two species, while the third species had a lower accuracy for the call-independent identification. Our results demonstrate that individual identification from bird song can occur even when direct comparison of a particular song type is not possible.

The acoustic properties of the environment influence sound propagation. Many previous studies examined whether various species of anurans, birds and mammals adjust usage and / or structure of their vocal signals to limit degradation during propagation in this environment (“acoustic adaptation hypothesis”). The present review examines how widespread such adaptations actually are across taxa. First, evidence or environment-related adjustments in usage of vocal signals is collected from studies in birds and other vertebrates (i.e., anurans and mammals). Second, a meta-analysis conducted by Boncoraglio & Saino (2007) on the influences of the environment on the acoustic structure of avian vocalisations is taken as a reference, and results from additional studies in birds are reviewed and compared to its conclusions. Finally, evidence from similar studies conducted in anurans and mammals is collected and discussed. Concerning the usage of vocal signals, evidence of environment-related adaptations in the few studies found was more widespread in anurans and mammals than in birds. Regarding structure of vocal signals, evidence from additional studies in birds did not completely confirm results of the meta-analysis of Boncoraglio & Saino (2007). Pooling all bird studies together presented minimum frequency, frequency modulations and frequency range as acoustic variables most often adjusted to the environment, in contrast to temporal features, repetition rate and maximum frequency. The few studies conducted in anurans and mammals did not allow the identification of specific acoustic variables that typically show environment-related variations. Overall, evidence for the acoustic adaptation hypothesis was not as widespread as expected across taxa. The different aspects of vocal behaviour adapted to environmental conditions varied according to the species and local habitats. Environment-related adjustments in structure of vocal signals seem to be constrained by call function in anurans and mammals. This effect was not examined in birds, but vocal learning does not appear to be a pre-requisite to environment-related adjustment in this group.