Vocal Individuality of Great Gray Owls in the Sierra Nevada

ABSTRACT The cryptic plumage and nocturnal nature of the great gray owl (Strix nebulosa) make it difficult to study in its densely forested habitat. We investigated whether the vocalizations of individual great gray owls could be distinguished and used as a tool for population survey and monitoring. We recorded 312 territorial calls produced by 14 male and 11 female great gray owls between March and July 2006 and 2007 in the Sierra Nevada range of California, USA. We recorded 19 owls on multiple occasions within a season and 8 owls between seasons. We extracted 17 frequency and 15 temporal variables from the sonograms of each call. Discriminant analysis selected 9 variables and classified 92.8% of calls to the correct individual within a season; 71.4% of calls were classified to the correct individual between seasons. Our results indicate that territorial calls could be used to monitor individual great gray owls for both short- and long-term studies. Vocal individuality could be useful as a noninvasive method to improve census estimates and yield information on site fidelity, turnover rates, seasonal movements, and behavioral traits of great gray owls.     

Vocal identification of individual African Wood Owls Strix woodfordii: a technique to monitor long-term adult turnover and residency

The hoot-calls of Wood Owls Strix woodfordii , recorded in the Kruger National Park, South Africa, from 1986 to 1998, are sufficiently different to distinguish individuals. Thirteen hoot-call variables, measured from recordings over this period, show that male and female Wood Owls have such temporal stability that these calls can be used reliably as a long-term census technique. manova , based on ordinations from principal component analysis, was used to identify individuals statistically between sampling periods. A forward stepwise discriminant function analysis achieved 100% classification success of individual male ( n  = 3) and female ( n  = 4) owls from a single sampling period. For all the individuals recorded over the whole study period we achieved a classification success of 80.9% ( n  = 9) for male hoot calls and of 96.3% ( n  = 13) for female calls. We found mean occupation periods of 82.25 and 65 months and annual turnover rates of 19.3% and 13.65% for males and females, respectively. Our survey, using vocalizations, is unique since we use data collected over a 12-year period to derive estimates of population turnover in Wood Owls, and consider what questions can be addressed in similar studies.     

RECENT BIOACOUSTIC PUBLICATIONS—from 1991 and a few from 1990 and 1989

ABSTRACT

The focus of this study was to determine whether individual vocal identification of Scops Owls Otus scops was possible and if there was a stability of the hoot-calls over a short time period in the same individuals. Spontaneous vocalizations of 13 owls were recorded in 2004 in Southern Tuscany, Italy. Visual analysis of spectrograms and quantitative multivariate analysis of six vocal features showed marked individual differences. In some owls a repertoire of two different hoot types was found. In 2005, 10 Scops owls were recorded three times in the same breeding season (2 hours and 10 days after the first session). Statistical analysis of data showed that 60% of owls did not change call features over time. However a slight but significant variability between successive vocal performances of the same owl was found in 40% of cases. This variability may decrease the recognition power by acoustic analysis. To overcome this obstacle I suggest a multi step qualitative/quantitative approach. A Difference Index (DI) was calculated to set a threshold between the slight intra-individual and the very high inter-individual variability. This method allowed the recognition of calls of each owl recorded over time in 2005.     

Variation in the male territorial hoot of the Tawny Owl Strix aluco in three English populations

Little is known about owl song. We made sonagrams of the territorial calls of 50 male Tawny Owls Strix aluco from three different areas. Six temporal and four frequency measures of the calls were recorded from the sonagrams. The measures of the calls were then subjected to analysis to try to separate between individual owls and between owls from different areas. We also looked for similarities between calls of neighbouring owls and for any effect of habitat on owl hoots. Individual owls were separated on the basis of their hoots with a high degree of success (98.6% overall), and there were significant differences between areas. Differences were found between calls in woodland and farmland habitats, but these differences were not in the direction expected to increase sound transmission. Calls of neighbouring owls did not resemble each other more than calls from owls that were not in vocal contact, implying that if calls are learned by Tawny Owls, they are learned before dispersal.     

IDENTIFICATION OF BRITISH BAT SPECIES BY MULTIVARIATE ANALYSIS OF ECHOLOCATION CALL PARAMETERS

ABSTRACT

Previous studies have found variability and individual distinctiveness in the echolocation calls of bats. We consider two implications of individually distinct echolocation calls: 1) whether bats may be able to use such variation to recognise familiar conspecifics, and 2) whether investigators could use such variation to identify known individuals or to census populations. We compared the discriminability of the echolocation calls of big brown bats (Eptesicus fuscus) recorded in three situations: (a) while held in the hand, (b) while perched on a platform, and (c) while flying in an anechoic chamber. Using variables describing each sonar call, we employed discriminant function analysis (DFA) to assign calls to recording situation or to bat. Discrimination of calls by recording situation was largely unsuccessful, although flying calls could be distinguished from platform calls. Assignment of calls to individual bat across recording situations yielded 72% success, and, within a given recording situation, yielded 87% success. Stepwise DFA reduced the number of variables needed to discriminate between individuals with only a slight decrease in correct classification. These results suggest that bats (or researchers) may be able to use the information contained in the echolocation calls for individual recognition. Individual distinctiveness raises the possibility of censusing bats by sound. We used cluster analysis in an attempt to determine whether, given a sample of calls from an unknown number of bats, a reasonable estimate of the number of bats could be obtained. Results were unsatisfactory, suggesting that cluster analysis probably will not permit acoustic censusing of bats in the field.     

Acoustic identification of eight species of bat (mammalia: chiroptera) inhabiting forests of southern hokkaido, Japan: potential for conservation monitoring

Assessing the impact of forest management on bat communities requires a reliable method for measuring patterns of habitat use by individual species. A measure of activity can be obtained by monitoring echolocation calls, but identification of species is not always straightforward. We assess the feasibility of using analysis of time-expanded echolocation calls to identify free-flying bats in the Tomakomai Experimental Forest of Hokkaido University, Hokkaido, northern Japan. Echolocation calls of eight bat species were recorded in one or more of three conditions: from hand-released individuals, from bats flying in a confined space and from bats emerging from their roost. Sonograms of 171 calls from 8 bat species were analyzed. These calls could be categorized into 3 types according to their structure: FM/CF/FM type (Rhinolophus ferrumequinum), FM types (Murina leucogaster, Murina ussuriensis, Myotis macrodactylus and Myotis ikonnikovi) and FM/QCF types (Eptesicus nilssonii, Vespertilio superans and Nyctalus aviator). Sonograms of the calls of R. ferrumequinum could easily be distinguished from those of all other species by eye. For the remaining calls, seven parameters (measures of frequency, duration and inter-call interval) were examined using discriminant function analysis, and 92% of calls were correctly classified to species. For each species, at least 80% of calls were correctly classified. We conclude that analysis of echolocation calls is a viable method for distinguishing between species of bats in the Tomakomai Experimental Forest, and that this approach could be applied to examine species differences in patterns of habitat-use within the forest.     

AUTOMATIC FEATURE EXTRACTION AND CLASSIFICATION OF CROSSBILL (LOXIA SPP.) FLIGHT CALLS

ABSTRACT

In this paper a new method for the automatic classification of bird sounds is presented. Our method is based on acoustic parameters (features) taken from the first harmonic component computed from the sound spectrogram. The features are based on a line segment approximation of the first harmonic component. The final feature vectors, consisting of 16 real numbers, are then classified using a self-organizing map (SOM) neural network. Flight calls of four crossbill species (Loxia spp.) are used as a test example. In the first phase, an unsupervised network was trained and tested using common crossbill L. curvirostra flight calls recorded mainly in the Netherlands. The network was tested using two-barred L. leucoptera, Scottish L. scotica and parrot L. pytyopsittacus crossbill flight calls in the second phase. Finally, the results were validated applying the same network to flight calls of common crossbills and parrot crossbills recorded in Finland. The method automatically separated common crossbill flight calls from those of parrot crossbills. The classification accuracy of the Dutch recordings was 58% in the first phase and 54% in the second phase. The Finnish recordings were classified with 54% accuracy.     

Variations in the echolocation calls of the European free-tailed bat

The echolocation calls of Tadarida teniotis were studied in an outdoor flight enclosure (captive individuals) and in the wild using single microphones or an array of four microphones. Calls were characterized by measures of 10 call variables. Comparison of individual calls recorded on four microphones arrayed in a tetrahedron with 1 m between each microphone revealed that all calls were not equally detectable by all microphones but that there were no significant differences in call features obtained from calls recorded on all four microphones. A comparison of 47 calls recorded by all four microphones showed no significant differences in the features of the four recordings of each call. Analysis of calls of five individuals flying individually in an outdoor flight cage revealed significant individual differences in call features. In the field, T. teniotis used long, narrowband search-phase calls, usually without harmonics. Analysis of 1876 search-phase echolocation calls of T. teniotis recorded in the field in Israel and Greece in 2002, 2005 and 2006 showed significant year-to-year and site-to-site differences in some call features. When flying in the presence of conspecifics, T. teniotis changed their echolocation calls. We found a range of different buzzes in the wild, and based on their structure we attempted to classify them as feeding and social buzzes. The features of individual calls comprising buzzes differed significantly among buzzes, and yet there were no consistent differences between what we classified as feeding and social buzzes.     

Localization of Passerine Seeet and Mobbing Calls by Goshawks and Pygmy Owls

Goshawks and pygmy owls responded to recordings of passerine alarm calls by correctly orienting to their source. The seeet, or “aerial predator” alarm call which is generally assumed to be “non-localizable”, while it elicited fewer responses than did mobbing calls, was nevertheless accurately localized by all birds that did respond. The evolution of alarm calls is discussed in terms of efficient prey communication, following Darwin's “antithesis principle”, rather than predator selection for non-localizability.     

中华蜜蜂形态遗传分析方法的研究

本文以3个中华蜜蜂Apis cerana cerana种群为模型,测定常用的30个形态变量数据,通过比较逐步判别分析、主成分分析、聚类分析等多种多变量统计方法的分析结果,找出适合划分中华蜜蜂种群、揭示种群间遗传关系的数据分析方法.结果表明:逐步判别分析对于划分中华蜜蜂种群效果最好,并可进行准确率检验;与聚类分析联用有助...     

Stability and change in the vocal signatures of common marmoset mobbing calls

Alarm calls that carry information about the identity of the caller may help the receiver decide how to react. We recorded the tsik calls of six captive adult marmosets (Callithrix jacchus) in two different social groups in response to snake models at two time points (summer 2014 and January 2015). We measured eight acoustic variables including duration, inter-call interval, minimum and maximum frequency, and starting, maximum and ending peak frequency. Discriminant function analyses (DFA) confirmed that calls were individually distinct at both time periods (78.88 and 79.89% correctly classified at time one and time two, respectively). Stability of the vocal signatures was assessed using the DFA model for summer 2014 to classify calls elicited in January 2015. Although the classification rates were lower in 2015, calls were still classified more than would be expected by chance (64.50%). This suggests that acoustic signatures of common marmoset tsik calls remain fairly stable over time and therefore remain recognizable by their groupmates. However, during that six-month period, at least three (out of seven) acoustic parameters changed such that they were significantly higher or lower in all six marmosets; in two marmosets six out of seven parameters changed. Changes to individual ‘voices’ of animals, despite overall stability reflected in above-chance matching of calls over time in a DFA analysis, may have implications for acoustic research.     

At sea vocal repertoire of a foraging seabird

Seabirds spend most of their time at sea, yet our knowledge of their activities and behaviour is limited due to difficulties of in‐situ data collection. In particular, we know virtually nothing about their acoustic communication when at sea. We benefited from the recent development of miniaturised audio‐recording devices to deploy acoustic recorders on breeding Cape gannets Morus capensis to study their vocal activity while foraging. Call sequences were recorded on 1718 occasions, from which acoustic variables were measured on calls with good recording quality. A total of 1348 calls from 18 birds were measured in temporal and frequency domains. Each call was assigned to a behavioural context defined acoustically: sitting on the water, flying, taking off or just before diving. Potential discrimination among calls from different contexts was tested using the random forest algorithm. Within each context, individual stereotypy in the calls was assessed per acoustic variable using a measure of potential of individual coding, and as a combination of variables using a similar multivariate analysis. The acoustic structure differed according to the behavioural context (global accuracy of prediction 75%). Temporal variables (sequence and call duration) were most important to correctly classify the calls among the four contexts. When considering only two contexts, on the water and in the air (merging flying and diving), frequency and spectral variables (percentage of energy below 1200 Hz and fundamental frequency) were of most importance (accuracy 86%). A combination of acoustic variables was necessary to discriminate individuals, but calls from all contexts were not strongly individually distinct (accuracy 41–63%). We provided the first detailed acoustic analysis of a foraging seabird and demonstrated context‐specific acoustic structure in its vocalisations at sea. Our results suggest that seabirds use vocal communication to exchange various types of information that likely improves foraging success.     

Acoustic divergence between bottlenose dolphin whistles from the Central–Eastern North Atlantic and Mediterranean Sea

To improve our understanding of the complex genetic and ecological structure of bottlenose dolphin (Tursiops truncatus) populations, we examined the acoustic features of communication signals from two geographically contiguous areas: the Central–Eastern North Atlantic and the Mediterranean Sea. Variations in the whistles were evaluated for four locations. Ten signal parameters were measured and used to statistically differentiate between the areas. Over 79 % of sightings were correctly classified by discriminant function analysis, confirming an acoustic differentiation between the two basins. The results of cluster analysis using the mean values of the parameters for each sighting showed that the three easternmost sightings from the Mediterranean and one sighting from the Canary archipelago formed a separate cluster from the rest of the Atlantic. The two sightings from the Alboran Sea in the west Mediterranean were grouped with the Atlantic recordings. There was more variability in whistles from the Atlantic Ocean consistent with data from genetic and photo-identification studies that document resident and non-resident animals in the area. The results suggest that the Alboran area may be inhabited by animals differentiated from the rest of the Mediterranean basin as a result of habitat features.     

Evaluation of two minimally invasive techniques for electroencephalogram recording in wild or freely behaving animals

Insight into the function of sleep may be gained by studying animals in the ecological context in which sleep evolved. Until recently, technological constraints prevented electroencephalogram (EEG) studies of animals sleeping in the wild. However, the recent development of a small recorder (Neurologger 2) that animals can carry on their head permitted the first recordings of sleep in nature. To facilitate sleep studies in the field and to improve the welfare of experimental animals, herein, we test the feasibility of using minimally invasive surface and subcutaneous electrodes to record the EEG in barn owls. The EEG and behaviour of four adult owls in captivity and of four chicks in a nest box in the field were recorded. We scored a 24-h period for each adult bird for wakefulness, slow-wave sleep (SWS), and rapid-eye movement (REM) sleep using 4 s epochs. Although the quality and stability of the EEG signals recorded via subcutaneous electrodes were higher when compared to surface electrodes, the owls’ state was readily identifiable using either electrode type. On average, the four adult owls spent 13.28 h awake, 9.64 h in SWS, and 1.05 h in REM sleep. We demonstrate that minimally invasive methods can be used to measure EEG-defined wakefulness, SWS, and REM sleep in owls and probably other animals.     

BOOK REVIEW

Echolocation calls of four species of insectivorous bats of central Chile were recorded and characterized to determine vocal signatures that allow their identification in the field. Pulses of Tadarida brasiliensis were characterized by the highest duration and the lowest values for all frequencies, which do not overlap those of the remaining species. Tadarida emits narrowband, shallow frequency-modulated search calls. All three vespertilionid species studied (Histiotus montanus, Lasiurus varius and Myotis chiloensis) showed similar echolocation design to one another, consisting of a downward frequency modulation at the beginning of the signal followed by a narrowband quasi-constant frequency component; however, their calls differ by their spectral characteristics. Discriminant function analysis of six acoustic parameters (duration, initial frequency, slope frequency modulation, peak frequency, minimal and maximal frequencies) gave an overall classification of 87.4%, suggesting species could be correctly classified based on echolocation calls. Call duration and minimal frequency were the variables most important for species identification.     

Auditory Perception of Hawks and Owls for Passerine Alarm Calls

The auditory perception of eight species of raptors was examined to test the hypothesis of Marler (1955) that these avian predators are unable to locate certain songbird alarm calls. In particular, Marler proposed that mobbing calls have characteristics that enhance their locatability and that these characteristics are absent in the high-frequency 'seet' calls given by individual songbirds. To test this hypothesis, the behavioral responses of four species of owls and four species of hawks, housed at two different raptor rehabilitation sites, to tape recorded alarm calls were examined. Each raptor was exposed to a random order of 10 trials of mobbing calls and 10 trials of a seet call. Responses were scored based upon head angle orientations. Hawks and owls responded more often and more accurately to mobbing calls than to seet calls. In general, owls responded to significantly more calls than hawks. The results are consistent with Marler's hypothesis that raptors have difficulty locating passerine seet calls. Nevertheless, future studies should test mobbing calls that vary in their frequency and duration ( Ficken & Popp 1996 ) to determine whether some mobbing calls are more difficult to locate than others.     

VOCAL INDIVIDUALITY IN MOTHER AND PUP SOUTH AMERICAN FUR SEALS, ARCTOCEPHALUS AUSTRALIS

South American fur seals breeding in Peru are subjected to levels of maternal aggression, and subsequent pup mortality, that are higher than has been reported for any other otariid species. For mothers and pups to maintain contact with each other, a mutual recognition system should exist to facilitate reunion and avoid misdirection of maternal effort. We recorded vocalizations of mothers and pups at Punta San Juan, Peru, during the 1994 and 1995 breeding seasons. Sixteen acoustic variables were measured from a total of 560 calls from 15 mothers and 13 pups. Multivariate analysis showed that calls were variable in several acoustic dimensions. While calls of both mothers and pups showed low variability within and high variability among individuals, mothers' calls were more individualistic. On average, discriminant-function analysis correctly assigned 60% of pup calls and 70% of mother calls to the individual that produced them. Characteristics of the fundamental frequency were most important for distinguishing among mothers, while pup calls, which typically contained less harmonic structure, could be differentiated by formant-like frequency ranges. Thus, calls of mother and pup South American fur seals appear to exhibit sufficient stereotypy to allow for recognition and discrimination among individuals.     

An evaluation of manual and automated methods for detecting sounds of maned wolves (Chrysocyon brachyurus Illiger 1815)

Although bioacoustics is increasingly used to study species and environments for their monitoring and conservation, detecting calls produced by species of interest is prohibitively time consuming when done manually. Here we compared four methods for detecting and identifying roar-barks of maned wolves (Chrysocyon brachyurus) within long sound recordings: (1) a manual method, (2) an automated detector method using Raven Pro 1.4, (3) an automated detector method using XBAT and (4) a mixed method using XBAT's detector followed by manual verification. Recordings were done using a song meter installed at the Serra da Canastra National Park (Minas Gerais, Brazil). For each method we evaluated the following variables in a 24-h recording: (1) total time required analysing files, (2) number of false positives identified and (3) number of true positives identified compared to total number of target sounds. Automated methods required less time to analyse the recordings (77–93 min) when compared to manual method (189 min), but consistently presented more false positives and were less efficient in identifying true positives (manual = 91.89%, Raven = 32.43% and XBAT = 84.86%). Adding a manual verification after XBAT detection dramatically increased efficiency in identifying target sounds (XBAT+manual = 100% true positives). Manual verification of XBAT detections seems to be the best way out of the proposed methods to collect target sound data for studies where large amounts of audio data need to be analysed in a reasonable time (111 min, 58.73% of the time required to find calls manually).     

Turnover of territorial Scops Owls Otus scops as estimated by spectrographic analyses of male hoots

In this study we assessed territory turnover of the European Scops Owl Otus scops, a migratory nocturnal raptor, using sonagrams of hoots recorded in the same territories in the 1993 and 1994 breeding seasons. Three structural parameters of the hoot (duration, inter-note interval and frequency) varied considerably, and a Discriminant Function Analysis classified >90% of individual calls correctly. In order to investigate yearly turnover and site-fidelity of male Scops Owls, the discriminant functions derived from the hoot sample recorded in 1993 were used to classify hoots of individuals recorded in the same territories in 1994. Apparently, turnover rate of territory owners was high and rapid, because 55–78% of territories censused in 1993 were defended by a different male in 1994. The fast decline of our Scops Owl population, probably due to winter mortality, could be responsible for such a high turnover of territorial owners.