mammals

In subterranean ecotope, where absence of light and ventilation limits visual and olfactory communication, options for long-range communication are restricted. Sound is thus one of the few channels available for transfer of the intraspecific information if the animals are not in direct contact. Nevertheless, even this kind of communication is limited by the acoustic conditions of the burrows. It is known that low-frequency sounds are best propagated here. In our study, we describe the vocal repertoire of the social subterranean rodent, the giant mole-rat (Fukomys mechowii, Bathyergidae), from mesic Afrotropics. Its vocal repertoire is shifted to lower frequencies than in other subterranean rodents. The giant mole-rat has the richest vocal repertoire among all subterranean rodents studied so far. In four behavioural contexts, we distinguished 14 single sounds of true vocalization and four types of mechanical communication. Additionally, one seismic (soil-borne) signal of unclear function has been identified. We suggest that the rich vocal repertoire is connected with rich social interactions in giant mole-rat families.

The Caviomorph rodents have precocious young and vary in social complexity, resorting to acoustic communication to efficiently regulate social interactions intra-group and to avoid intruders and predators. The wild cavy Cavia aperea, one of the species with the largest geographic distribution, is considered a wild representative of the domestic Cavia porcellus, a species with a remarkable acoustic repertoire. We conducted a descriptive study on the acoustic behaviour of a captive population of C. aperea. We observed animals in groups, in pairs and isolated pups, and conducted sonographic and descriptive analyses. Ten distinct call types were identified: teeth-chattering, structurally variable contact calls, whines and squeals, a scream, alarm whistle, almost exclusive pup-isolation whistle and tweet calls, and the previously described alarm drrr and courtship purr calls. As in other caviomorphs, some of these signals may carry information about specific contexts and moods and others may communicate arousal. The similarity of this repertoire size to that of C. porcellus shows that the richness of the latter is not a product of domestication. Instead, it may be associated with a relatively complex social life and other ecological factors. Our data set the groundwork for comparative studies of the evolution of acoustic communication.

We describe the interactive nature of vocalizations emitted by African elephant (Loxodonta africana) family groups while visiting waterholes. Despite being in close visual contact with each other, individuals called interactively within a series of overlapping or antiphonal vocal bouts that increased significantly while departing from the waterhole. After initiating departure from the waterhole, elephants in this study increased their calling rate and their production of overlapping vocal bouts. The majority of calls either overlapped or occurred within 1.5 seconds of another call as part of an antiphonal bout, rather than as isolated calls. The departure of larger herds was accompanied by a greater number of calling bouts. The increase in interactive antiphonal bouts during departure might serve to facilitate group coordination and cohesion, as well as possibly reinforce social bonds. The longer repeated bouts could also facilitate eavesdropping by distant elephants by boosting signal detection since the repetition of these longer calls may yield an increase in the signal-to-noise ratio (SNR) that reduces the noise floor for better longer distance communication.

Stereotypic behaviour, such as territorial calls and songs, is thought to be evolutionarily conserved, and therefore useful in discerning systematic relationships. We examined vocalizations of several species of Peromyscus and Onychomys, a monophyletic group of rodents (Peromyscini). We report stereotypic vocal signals occurring in both sexes of the deer mice Peromyscus californicus, P. eremicus, P. leucopus, P. melanophrys, P. polionotus, and the grasshopper mice Onychomys arenicola and O. leucogaster. The stereotypic vocalizations of P. eremicus, P. leucopus, and P. polionotus are confined to frequencies greater than 20 kHz, unlike those of Onychomys, which are clearly audible, or P. californicus and P. melanophrys, which generate lower frequency vocalizations than the other Peromyscus. We did not observe stereotypic vocalizations in P. aztecus. Intensity, context and consistency suggest that these vocalizations serve an announcement function. Distribution of spectral energy distinguishes genera and most species, and some use of frequency is correlated to body size. There is a dichotomy between Onychomys and Peromyscus in the use of frequency, a genus-specific pattern identified previously among other peromyscine lineages.

A new method for the automated detection of sperm whale clicks that combines neural network and statistical computations is presented. This method is intended to detect regular clicks and creaks and can be broken down into two main processing stages. The first stage works with the spectrogram output by computing the accumulated energy along each time frame, extracting consecutive two-seconds length time windows, obtaining statistical parameters characterizing these time windows and classifying them using a feed forward neural network as either containing regular clicks, creaks or noise. In the final stage a dynamic energy-based criterion is applied to each classified time windows based on previously computed statistical parameters. The performance of the method has been tested with three long recordings containing regular clicks and creaks and shows significantly high percentages of correct detections (global score of 94.8%) with a reduced computation time.

The minke whale (Balaenoptera acutorostrata) is a small, elusive baleen whale that is rarely sighted in tropical waters of the North Pacific Ocean. During winter and spring, they produce songs, also known as ‘boings’, that are commonly detected at deep water hydrophones located around the Hawaiian Islands. We acoustically monitored minke whales using a fixed seafloor hydrophone array encompassing a large ( >2000 km2), deep-water area off the island of Kauai. Simultaneous visual-acoustic surveys of the same region were conducted from a quiet motor-sailing vessel. The combination of the towed and fixed hydrophone arrays allowed animals to be localized and tracked in near real-time. Using both methods, we were able to visually confirm the location of a minke whale initially detected and localized using the fixed hydrophone array, and later with the towed hydrophone array. These data are being collected to help validate statistical methods that are being developed to estimate densities of marine mammals using acoustic signals they produce. In a related study, boings recorded in the Hawaiian Islands (central North Pacific) were acoustically characterised and compared to boings recorded in the western and eastern North Pacific. These results are discussed in relation to the behaviour and population biology of this species. We provide recommendations for tracking, monitoring behaviours and estimating the distribution and distribution of these vocally active, but visually elusive whales.

The NEMO-OvDE platform, deployed on the seabed at a depth of 2050 m, 21 km off the coast of Catania in Sicily (Italy), has provided the opportunity to better understand the presence and behaviour of sperm whales in the area. Equipped with four wideband hydrophones (30Hz-40kHz) forming a tetrahedral array of 1 m side, the platform sent digital data to the land station continuously 24h a day from January 2005 to November 2006. 7359 samples, for a total of 613 hours, were recorded and analyzed to determine the presence of sperm whales. Analyses were performed by trained operators with the use of SeaPro, a real-time spectrographic software, to distinguish species, number of individuals present and sound categories emitted. Sperm whale presence is considered as low density in the Ionian sea by an acoustic survey of IFAW in 2004 and by other works done in the vicinity. However, in our study, an unexpected presence of animals was found, with 23% of files containing animals in both years. Then, we focused our study on codas, sounds typical of social groups and with a geographical connotation, which for the Mediterranean are usually emitted as the 3+1 pattern. Not enough is known about the Mediterranean population to determine the connections between geographical areas. 3+1 remains the most common pattern, but a surprising variety of patterns was found, linking these animals to the situation present along the Hellenic trench. We used GAMs to establish seasonal variations to understand the movements of the species in the Ionian sea. Spring is the season richest in codas due to the greater presence of individuals. For the first time we demonstrate a relation between the pattern performed and the number of animals. This can be interpreted as an evidence of a different behavioural meaning.

Only a few is known about alarm calls of the European ground squirrel (Spermophilus citellus) (EGS) and the recently described Taurus ground squirrel (S. taurensis) (TGS). The aim of our study was to conduct detailed analysis and comparison of calls in these species. We also tested the potential of calls to code information about callers´ identity. Calls were recorded during summer 2007 and 2008 in colony of EGS in Prague, Czech Republic and in colony of TGS near Akseki, Turkey. Recorded calls were emitted toward humans by individuals sitting in entrances of their burrows. 600 calls (30 per individual) from 20 individuals (10 per species) of the EGS and the TGS were analyzed. In both species, alarm calls are tonal sounds usually consisting of two different elements. Both species significantly differ in several spectral and temporal parameters. Discriminant analysis classified more than 96 % of calls to a correct species. Calls in the EGS as well as in TGS were highly individually distinct. Discriminant analysis correctly classified 98 % of calls in the EGS and 94 % of calls in the TGS. Acoustic analysis revealed that the EGS and the TGS can be distinguished on the basis of their calls and support conclusions that vocalizations represent good features supporting species designations. We also established a big potential to recognize individuals on the basis of acoustic structure in their calls. Supported by the Ministry of the Environment of the Czech Republic (grant No. VaV/620/1/03 and No. SP/2d4/61/08).

Wolf chorus howls are complex vocalizations that play an important role in wolves acoustic communication. Most of the vocalizations included in these choruses are harmonic sounds and can be considered as chirp functions (functions with a fundamental frequency that change over time). The chirplet transform for acoustic signals yields an accurate signal approximation of the instantaneous frequencies (IF) and the chirp rates (IF rate of change) of harmonic signals. This allows us to decide if two instantaneous frequencies close in time belong to the same sound. We are testing an algorithm based on the chirplet transform properties for separating multiple voices emitted simultaneously in chirp functions. When a local maximum of the amplitude is found, the algorithm looks for the chirp “track” in the frequency/time domain, considering the instantaneous frequency and chirp rate estimated. With this algorithm, which we call “bloodhound”, we are able to separate multiple voices into voices emitted by single wolves in a chorus context. Besides counting individuals vocalizing simultaneously, this method could be used in measuring acoustic features of different vocalizations automatically, representing an important tool for the study of acoustic communication.