ultrasound

In Malaysia, males of the noctuid moth Amyna natalis were observed producing a continuous ultrasonic song of high intensity (about 102 dB SPL measured at a distance of 10cm). The frequency spectrum of the sound impulses had its peak between 60 and 80 kHz. During song production the animals were perching on plants and moving their wings up and down quickly. Simultaneously, by twisting the wings it seems likely that a male-specific “bubble'' in the forewing functions as a tymbal, resulting in sound production.

We recorded echolocation and ultrasonic social signals of the bat Myotis septentrionalis. The bats foraged for insects resting on or fluttering about an outdoor screen to which they were attracted by a 'backlight'. The bats used nearly linearly modulated echolocation signals of high frequency (117 to 49 kHz) with a weak second harmonic. The orientational signals from patrolling bats were about 2.4 ms in duration and occurred at a repetition rate of about 18 Hz. The signals used by bats as they approached the screen were of shorter duration (0.72 ms) and occurred at higher rates (33.8 Hz). We registered one feeding 'buzz'. We recorded social signals when two bats patrolled the hunting area. The social signals were characterized by their longer durations (6 ms), lower frequencies (70 to 30 kHz), and curvilinear sweeps. We calculated the source levels of orientational and social signals using the differences in arrival times at three microphones in a linear array. The source levels were on average 102dB peSPL at 10 cm. We could not calculate source levels of the signals used by bats as they approached the screen at close range, but these signals were much weaker (about 65d8 peSPL at the microphone).

No matter how perfect the recording equipment may be, there are acoustical influences that change signals in various ways. It may become impossible to decide just what the ‘real' signal is like in detail for there may be no simple answer. Such considerations can relate to any examples of communication but they become especially significant for ultrasound and may pose important problems for echolocation.

Comparative studies of sound production and sound emission in seven species of European tettigoniids have been carried out. The species chosen were two Tettigoniines (Tettigonia cantans, Tettigonia viridissima), two Ephippigerines (Ephippiger discoidalis, Ephippiger ephippiger), and three Decticines (Decticus albifrons, Decticus verrucivorus, Psorodonotus illyricus). The factors which determined the choice of species were the different morphology (for example body shape and weight, and wing size) of the three subfamilies. The parameters of the different songs (e.g. dominant frequency, intensity) are normally not correlated to any of the investigated morphological characteristics of the animals. In the brachypterous species intraspecific correlations exist between wing size and the dominant low frequency band of the call. This frequency band is also observable at related higher frequencies in the ultrasonic range (20-60 kHz), the observed band width increasing with frequency. Sound emission in all species is to some extent directional. This directionality is related to body size and wing structure. The song structure of the different species does not appear to be related to any observable characteristic of the habitat of the animals. A possible exception may be the song of Psorodonotus illyricus with a particularly low dominant frequency band. The pathogenetic development of the songs seems to be determined by relationships between the different species rather than to any factors contributed by the habitat.

The Atlantic humpback dolphin Sousa teuszii is endemic to the west coast of Africa and is poorly studied. During January 2008, 2.7 hr of acoustic recordings were made during 11 S. teuszii encounters in the Namibe province of Angola. Echolocation click trains were audible in most recordings. A total of 298 individual dolphin whistles were recorded, of which 86 were of sufficient signal to noise ratio for the measurement of 10 fundamental frequency variables. Sousa teuszii whistles occurred in the 2.5 to 23.4 kHz fundamental frequency range and were relatively simple in structure, with 85% having a single inflection point. The fundamental frequency was relatively low, with mean minimum and maximum frequencies of 4.8 and 8.2 kHz respectively. Harmonics occurred in 92% of whistles, sometimes extending beyond the 44 kHz recording range. The most frequently recorded contour categories were convex and concave, and very few whistles exhibited complex modulation. The whistles produced by S. teuszii are broadly comparable with those published for the Indo-Pacific humpback dolphin S. chinensis. Future studies should consider context-specific use of whistle types, and should include comparisons with S. teuszii groups in other geographic locations to ensure the full species’ whistle repertoire is adequately characterised

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.

This study presents the first detailed description of the oscillographic structure and spectrographic features of sound emission produced by Z- and E-strain males of Ostrinia nubilalis during their courtship behaviour. Males simultaneously produce ultrasonic and low-frequency sonic sound emissions during their courtship, vibrating their wings at a distance of 1-2 cm from the female. The sound emission shows two characteristic types: a long courtship song is followed by a short precopulation song after a few seconds of silence. The ultrasonic courtship song is composed of pulses repeated in pairs or more typically in long series with an even repetition rate (which showed to be temperature dependent) or in irregular sequences. The precopulation song is a short crescending pulse-series. In both song types the ultrasonic carrier-wave has constant frequency spectrum containing components from 20 kHz to 80 kHz. The low-frequency sound emission has a harmonic frequency spectrum (fundamental frequency between 40-70 Hz). During the precopulation song the low-frequency component shows a characteristic frequency sweep from 80-100 Hz to 70-80 Hz. No significant difference has been noticed comparing the songs of Z- and E-strain males of O. nubilalis. However sound emission is clearly different from that described recently in the closely related O. furnacalis, where pulses are performed in groups forming chirps and no different courtship song and precopulation song has been described. The possible signal function of low-frequency near field sound emission is discussed.

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.

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.