mammals

Italian wolf howls are described for the first time from observations between 2003–2008 of a population living in eastern Tuscany, central Italy. A sample of 37 howls selected among single responses and 128 howls included in the choruses of 7 free ranging packs was recorded and analysed. The mean fundamental frequency of the howls ranged between 274–908 Hz. Two main structures recognised by means of multivariate explorative analysis, in particular Principal Component and Cluster Analysis, were ascribed to breaking and flat howls. Discriminant Function Analysis was applied to the recognised groups with the aim to find a general rule for classification. Howls with different features were correctly assigned to the groups obtained by explorative analysis in 95.8% of cases. The analysis of the variables characterising the structure of the howls suggests that maximum frequency and range of fundamental frequency are the most important parameters for classification, while duration does not appear to play any significant role.

Although ultrasonic vocalizations (USVs) have been recorded in many species of rodent and in various contexts, e.g. sexual behaviour and aggression, it has not been demonstrated for the endangered Turkish Spiny Mouse Acomys cilicius Spitzenberger. This study investigated whether A. cilicius emits USVs and, if so, how these USVs associated with non-vocalization behaviour. Ultrasonic recording equipment was set up for 12 days in an off-exhibit enclosure of A. cilicius at Bristol Zoo. At least seven different types of USV were recorded. For eight of the 12 study days, ultrasonic and video recording equipment were run concurrently. From these observations it was found that emission of USVs were associated with sexual behaviour, aggression and social investigation. The results of this study show for the first time that captive A. cilicius produce USVs that resemble those produced by other rodent species, including its close relative the Egyptian Spiny Mouse A. cahirinus Desmarest. As these findings apply only to a captive Turkish Spiny Mouse population, additional work should be carried out to investigate the behaviour and USV production in the wild in addition to further research on captive populations investigating the apparent communicative function of these vocalizations.

The pulsed calls of Long-finned Pilot Whales Globicephala melas have received little study, and their structure and function remain unclear. We examined the pulsed calls of Pilot Whales off Nova Scotia by taking multiple measures of 419 spectrograms from recordings made over a span of eight years. The results offer a quantitative description of pulsed call structure necessary for subsequent analysis of signal functionality and social relevance. Pilot Whale pulsed calls were found to be physically complex, with multiple, independently modulated components that are likely rich in information and difficult for eavesdroppers to imitate. The production of such structurally complicated signals suggests they play an important role in Pilot Whale communication. The pulsed calls appear to form two main call types: those with a maximum visible sideband above 18 kHz and those with a maximum visible sideband below 15 kHz. However, there is no indication of further discrete categories despite a large amount of variation between calls within those two broad categories. The high variation in call structures may indicate communicative plasticity, allowing the whales to communicate state, such as level of arousal, and to compensate or variable background noise levels. The structural similarity of Pilot Whale and Killer Whale Orcinus orca pulsed calls raises the question of whether the distantly related whale species, with a shared but rare social structure, have evolved similar call structures to solve similar communication challenges.

Probably all odontocetes use echolocation for spatial orientation and detection of prey. We used a four hydrophone “Y'' array to record the high frequency clicks from free-ranging White-beaked Dolphins Lagenorhynchus albirostris and captive Harbour Porpoises Phocoena phocoena. From the recordings we calculated distances to the animals and source levels of the clicks. The recordings from White-beaked Dolphins were made in Iceland and those from Harbour Porpoises at Fjord & Bælt, Kerteminde, Denmark during prey capture. We used stringent criteria to determine which clicks could be defined as being on the acoustic axis. Two dolphin and nine porpoise click series could be used to track individual animals, which presumably focused on the array hydrophones or a fish right in front of the array. The apparent source levels of clicks in the individual tracks increased with range. One individual White-beaked Dolphin and three Harbour Porpoises regulate their output signal level to nearly compensate for one-way transmission loss while approaching a target. The other dolphin regulated the output differently. For most of the recordings the sound level at the target remains nearly constant and the echo level at the animal increases as it closes on the target.

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.

Neotropical primates have evolved long calls, which have a role in spacing and cohesion of groups. Detection and “reading” of long calls as well as ranging of calling individuals seem essential for this role. This study used sound propagation experiments to investigate habitat caused degradation of long calls of the Golden Lion Tamarin Leontopithecus rosalia and its implications for “reading” and ranging long calls of calling tamarins. The experiments were made in lowland, evergreen forest in Brazil. Synthesized copies of natural sounds were broadcast and re-recorded using different combinations of microphone and speaker heights of 2.0 and 7.5 m and distances of 2.5, 10, 20, 40 and 80 m. Excess attenuation, blurring, signal-to-noise ratio and energy of tail of echoes were quantified. The highest frequency sounds attenuated most at all distances, showing the lowest signal-to-noise ratio. The more effective sound propagation at 2.0 m (below the canopy and in the upper part of the dense undergrowth where they forage) facilitates reading of the information content of the long calls and hence their use for communication during foraging. Although the high degradation of the long calls with distance at microphone and speaker heights of 7.5 m (inside the canopy) constrains reading of the long calls’ information content it does provide very good conditions for ranging and may be one of several reasons for why long-calling tamarins approach long-calling neighbours through dense vegetation for group encountering.

Bats of the genus Myotis cannot be identified reliably using conventional acoustic analyses. Here we use morphology of echolocation calls to discriminate between Myotis spp. This method may be used to identify unknown roosts to species level in the field. Echolocation calls of M. daubentonii, M. mystacinus and M. nattereri, were recorded in emergence flights from roosts. Images of echolocation calls were extracted for morphological analysis performed in SHAPE, a program that transforms twodimensional outline data into Elliptic Fourier Descriptors. Species typical call shapes were described with Mahalanobis models. Discriminant Function Analyses (DFA) were applied with Mahalanobis scores of typical shape alone and with a spectral call parameter, maximum frequency. DFA achieved an overall correct classification rate of 88.9% using typical outline shapes alone. Correct classification of 100% of both M. daubentonii and M. mystacinus was achieved by both typical call outlines. For M. nattereri, 79.6% of calls were correctly classified by call morphology, but the addition of maximum frequency improved this to 96.3%. Shape analyses provide a quick and easy method of distinguishing Myotis species under field conditions and could be extended to include other species of bats that share conventional acoustic parameters.

In most mammals, adults produce relatively low frequency vocalizations compared to those of juveniles. This rule is not maintained however at least in four species of ground squirrels, whose juveniles call at the adult's fundamental frequency. These findings have been obtained however with separate sets of juveniles and adults and no data is available concerning the ontogeny linked to these differences. Here we analyze the acoustic structure of alarm calls of the same Yellow Spermophilus fulvus and Speckled S. suslicus ground squirrel individuals, recorded as pups and as adults after hibernation. We found the fundamental frequencies of adults within the same frequency ranges as those of pups, in spite of the significant difference in body mass. In ground squirrels, severing the relationship between body size and call frequency removes some vocal cues to age. We discuss some functional hypotheses advanced to explain manipulations with fundamental frequencies in ground squirrels and other animals, and suggest the lack of data for discussing the mechanisms of such vocal tuning.

Vocalizations of many mammalian species have been reported to encode information about caller identity. In this study, we analyzed 300 alarm calls from 10 free-living European Ground Squirrels Spermophilus citellus (30 per individual) and 300 alarm calls from 10 free-living Taurus Ground Squirrels S. taurensis (30 per individual), and tested the potential of these calls to encode information about the callers' identities. Discriminant analysis including all 10 European Ground Squirrel individuals correctly classified 98% of calls, and cross-validation reached a classification success of 97%. Correct classification of 98% and cross-validation of 98% was assigned when the analysis included only those individuals producing calls consisting of both elements (eight individuals). For the Taurus Ground Squirrel, correct classification was 95% and cross-validation 94% for all 10 animals. When only those individuals producing calls consisting of both elements were included (eight individuals), discriminant analysis led to 94% correct classification and cross-validation produced a classification success of 93%. These analyses demonstrate that the structure of alarm calls in these two closely related species is highly variable and that it has significant potential to encode information about caller identity.

Sound plays an important role for toothed whales in foraging and communication. However, little is known about acoustic communication in the toothed whale species that only produce narrow band high frequency (NBHF) clicks, such as the harbour porpoise Phocoena phocoena. To study acoustic behaviour and to quantify the source parameters of porpoise communication signals, the acoustic and swimming behaviour of three adults and one calf were recorded using an array of hydrophones, acoustic tags and an overhead video camera. We tested the hypothesis that different behavioural interactions between porpoises involve specific click patterns for communication and measured the source characteristics of these click patterns to estimate the active space of porpoise click communication. Our results provide strong evidence that porpoises communicate acoustically using specific patterns of clicks with source properties comparable to normal echolocation clicks, and that they employ stereotyped aggressive click patterns, exposing conspecifics to received levels of up to 180 dB re 1 µPa (pp). The measured source properties render estimated active spaces of less than 1000 meters for porpoises' communication sounds. Compared to other cetaceans, porpoises must therefore remain much closer to be able to communicate acoustically.