mammals

The use of bat detectors to monitor bat activity is common. Although several papers have compared the performance of different brands, none have dealt with the effect of different habitats nor have they compared narrow- and broad-band detectors. In this study the performance of four brands of ultrasonic bat detector, including three narrow- band and one broad-band model, were compared for their ability to detect a 40 kHz continuous sound of variable amplitude along 100 metre transects. Transects were laid out in two contrasting bat habitat types: grassland and forest. Results showed that the different brands of detector differed in their ability to detect the source in terms of maximum and minimum detectable distance of the source. The rate of sound degradation with distance as measured by each brand was also different. Significant differences were also found in the performance of different brands in open grassland versus deep forest. No significant differences were found within any brand of detector. Though not as sensitive as narrow-band detectors, broad-band models hold an advantage in their ability to identify species where several species are found symmetrically.

Bat detectors are commonly used to monitor bat behaviour. Earlier research has suggested that there may be systematic differences in the response of different detectors to bat calls. Such differences would have important implications for the comparability of quantitative surveys conducted with bat detectors. The present study examines variability within and between brands of bat detector in accuracy of tuning, directionality and sensitivity to different types of bat echolocation call in bat detectors from three manufacturers. The consistency of results from a field survey incorporating the three brands in a standardised methodology are also examined. Significant differences were found within and between brands in directionality and sensitivity which would lead to bias in bat surveys. The implications of these findings for bat surveys are discussed, as are the design features of importance for species identification.

The vocalizations emitted by adult female domestic goats in response to their offspring's bleats were recorded, and sonograms were made and analyzed. The calls were segmented, atonal, and broad banded between 200 and 4,840 Hz. The energy was concentrated, on the average, around 1,258 Hz, a frequency close to the optimal hearing capabilities of the species. There were statistically significant individual differences for duration, number of segments, number of harmonics, peak frequency and fundamental frequency. Furthermore, using a discriminant function analysis we were able to correctly assign 76% of the calls to the individuals that emitted them. We concluded that the does have individually distinctive vocalizations, and that the physical characteristics of the bleats allow for locatability and ease of detection of the signal. Therefore, it is possible for the kids to be able to recognize and locate their mothers on the basis of auditory cues.

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).

A sonographic analysis of the structure of fox vocalisations, based on 512 adult and 73 cub vocalisations obtained from archive recordings, was combined with field data on the vocal behaviour of an urban fox population. Calls were described quantitatively by six variables: duration, lowest and second lowest frequency bands (from sonagrams), highest and second highest peak frequencies (from power spectra) and the number of components. They were separated into 20 call types, eight of which were cub vocalisations. Call types were used singly or in combination, and some gradation between particular call types was apparent. Hypotheses regarding call function were generated based on the matching of acoustic properties with their seasonal occurrence and the socioecological pressures acting on foxes at different times of the year. Calls that were structurally suited to agonistic and contact functions were found to be significantly more common during the winter, the time of mating and dispersal, when foxes move over greater areas.

We investigated the problem of categorizing the repertoire of a group of highly varied vocalizations. A set of Weddell seal Leptonychotes weddelli in-air calls recorded near Davis, Antarctica, were examined. The repertoire size was estimated by first subjectively assigning each call (based on auditory and spectrographic patterns) to one of a large number of provisional call types. A set of frequency, duration and waveform measurements were made on every call. For each provisional call type, the mean value of each of these measures was calculated. These mean values were used to perform Cluster Analyses of the provisional call types. Beginning with calls clustered closest together, the most similar provisional call types were successively amalgamated until further joining would link two clearly dissimilar vocalizations (rising versus falling frequency sweeps in this case). The Weddell seal repertoire contained 12 call types ranging from long sinusoidal upsweeps to growls. This procedure provides a method of estimating the minimum repertoire size of a sample of calls. Dichotomous Sorting using Principal Components Analysis can also be used to categorize calls but will probably be of greater value when applied to finding subdivisions within a single call type.

Timber wolf Canis lupus pups vocalize within hours of birth. In this report we examine aspects of the acoustical structure of these vocalizations. We installed an unobtrusive monitoring system in a den excavated by a group of pack-reared timber wolves at the Dalhousie Animal Behavior Field Station in order to observe and record at close range the activities of a female wolf with her litter of pups. We obtained audio and video recordings from birth through the first six postnatal weeks, after which time the pups emerged from the den. The audio recordings were analyzed spectrographically and the vocalizations were classified according to gross spectral type, duration, presence and rate of frequency modulation, and spectral bandwidth. Joint differences in at least two dimensions were necessary to classify vocalizations. The most common sounds, present as early as day one, were harmonically structured, with fundamental frequencies that decreased with age. Other vocalizations, which were rare and resembled recognizable adult sound types, were not apparent until after the second postnatal week.

A variety of structural parameters were measured from wolf choruses recorded in the Superior National Forest, Minnesota, USA. Mean duration of 60s did not vary with pack size or composition. Packs replied to simulated howling after an average of 40s, often interrupting the stimulus howls. Choruses began with simply-structured howls, which became increasingly modulated as the chorus progressed. Little difference in mean fundamental frequency or other howl parameters was found among the choruses from packs of various sizes and compositions. In particular, choruses produced by single adult pairs did not differ from those of larger packs accompanied by pups. The lack of relationship between chorus parameters and pack size or composition indicates there is little useful information concerning a pack's size to be found in its chorus howling.

The observation that chorus howling by adult pairs is often perceived as that of larger groups with pups suggests that chorus structure has evolved to exaggerate the apparent size of the pack, especially those newly-established or otherwise reduced in number. If so, wolf howling choruses may represent a mammalian example of the Beau Geste effect, made particularly viable because of the relative immunity of the signal to probing.

A phylogeny of guenons was drawn up from the analysis of the acoustic structure of their cohesion, contact and alarm calls, as well as of the loud calls of the adult males. The plesiomorphic or anamorphic state of every acoustic parameter retained was inferred from comparisons with calls given by papionines and/or colobines. A cladistic method was used for analysing a matrix of species by character.

The proposed phylogeny separates guenons into two groups: the one includes all forest-living arboreal forms, the other most of the terrestrially-adapted species. The latter, together with C. nigroviridis, which lie close to the origin from which all guenons diverged, share a relatively primitive position, while the arboreal species are the most derived living representatives of the taxon. Quite reliable interspecific affinities are found among arboreal forms, while there are some inconsistencies for the more primitive species. Such results suggest that cercopithecines would have undergone a radiation from more or less open habitats into forests, the evolution proceeding from large-bodied, partly-terrestrial forms to smaller arboreal ones.

The substitution method was adopted from industrial acoustics (Francois and de Montussaint 1972) to “eliminate the influence of the environment'' on measurements of the amplitude of vocalizations given by blue monkeys Cercopithecus mitis and grey-cheeked mangabeys Cercocebus albigena. Measurements were conducted of sound power and sound pressure level of representative utterances. Monkey vocal radiation patterns were also measured. The results showed that vocal amplitude ranged from 62 dB to 100 dB in sound pressure (re l pw). At a distance of 2 m, the loudest calls approached an amplitude of 110 dB SPL, a level about equal to the loudest human yell. The measurements of call amplitude conducted here exceeded those derived from the field by approximately 10 dB. It was shown that the discrepancy in amplitude between these laboratory based measurements and earlier measurements conducted under field conditions (Waser and Waser 1977) was probably due to destructive interference between the direct wave and the “ground wave'', a phase shifted wave reflected from the ground. Measurements of radiation patterns of primate vocalizations showed that, like human speech, directivity was a function of frequency, with high-frequency components being radiated mote directionally than lower-frequency components. However, primate utterances were in general radiated more omnidirectionally than was human speech.