Richard W. Hedley

Composition and sequential organization of song repertoires in Cassin’s Vireo (Vireo cassinii)

AbstractThe rules governing bird song sequences vary considerably across the avian phylogeny, and modifications to these rules represent one of the many ways in which bird song varies interspecifically. Cassin’s Vireo (Vireo cassinii) is one species that shows a highly structured syntax, with clearly non-random patterns of sequential organization in their songs. Here I present a description of Cassin’s Vireo song sequences from the Sierra Nevada Mountains in California and employ network analysis to quantify transition patterns within the songs. Repertoire sizes varied between 44 and 60 phrase types per bird for the 13 birds analyzed here. The repertoire was subdivided into ‘themes’ containing between two and seven phrase types. The birds sang the phrase types in a given theme for a time before eventually introducing a new theme; in this manner the repertoire was revealed relatively slowly over time. Theme composition within a bird’s repertoire did not change within or between singing bouts throughout the season. The tendency to sing in themes was corroborated by network analysis, which revealed small-world structure in the songs. Phrase types were widely shared within the population. I discuss these findings as they compare with the singing styles of other species, both closely and distantly related.ZusammenfassungZusammensetzung und sequenzielle Organisation der Gesangsrepertoires von Cassinvireos (Vireo cassinii) Die Regeln, welche die Gesangssequenzen von Vögeln regulieren, variieren beträchtlich zwischen Arten, und Modifikation dieser Regeln repräsentiert eine von vielen Weisen, auf die Vogelgesang interspezifisch variiert. Der Cassinvireo (Vireo cassinii) ist eine Art, die eine stark strukturierte Syntax aufweist, mit eindeutig nicht-zufälligen Mustern sequenzieller Organisation in den Gesängen. Hier präsentiere ich eine Beschreibung von Gesangssequenzen des Cassinvireos aus dem Sierra Nevada-Gebirge in Kalifornien und wende Netzwerkanalyse an, um Überleitungsmuster innerhalb der Gesänge zu quantifizieren. Die Größe des Repertoires variierte von 44 bis 60 Phrasentypen pro Vogel für die 13 hier analysierten Vögel. Das Repertoire wurde in „Themen“untergliedert, die zwei bis sieben Phrasentypen enthielten. Die Vögel sangen die Phrasentypen in einem bestimmten Thema für eine gewisse Zeit, bevor sie schließlich ein neues Thema einführten; auf diese Weise wurde das Repertoire relativ langsam über die Zeit hinweg offenbart. Die Themenkomposition innerhalb des Repertoires eines Vogels veränderte sich nicht innerhalb von oder zwischen Gesangsperioden im Verlauf der Saison. Die Tendenz, in Themen zu singen, wurde durch die Netzwerkanalyse bestätigt, die eine Kleine-Welt-Struktur in den Gesängen aufzeigte. Phrasentypen wurden in der Population weithin gemeinsam benutzt. Ich diskutiere diese Befunde im Vergleich mit den Gesangsstilen anderer nah und entfernt verwandter Arten.

Using Song to Identify Cassin’s Vireo Individuals. A Comparative Study of Pattern Recognition Algorithms

In this paper, we present a comparative study on the application of pattern recognition algorithms to the identification of bird individuals from their song. A collection of experiments on the supervised classification of Cassin’s Vireo individuals were conducted to identify the algorithm that produced the highest classification accuracy. Preliminary results indicated that Multinomial Naive Bayes produced excellent classification of bird individuals.

Fast 3D AML-Based Bird Song Estimation

In this paper, we present simulations and experimentally collected bird song data collected using a modified Voxnet acoustic array node (with four microphones) to perform 3D direction-of-arrival (DOA) estimation of various bird sources. We used the Approximate Maximum-Likelihood (AML) algorithm to construct the steering matrix in the beamforming process for the estimation of the DOA of the bird signals. While the computational burden is high in the 3D scenario, various strategies have been developed to reduce the computational burden of the algorithm for potential real-time applications. Extensive simulations and experimentally collected data are used to validate the effectiveness of the AML algorithm for 3D estimations and the usefulness of the modified Voxnet node. Both the estimated azimuths and elevations have approximately plus and minus 10 degrees of errors.

HARKBird: Exploring Acoustic Interactions in Bird Communities Using a Microphone Array

Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan E-mail: reiji@nagoya-u.jp ∗2Department of Ecology and Evolutionary Biology, University of California Los Angeles Los Angeles, CA 90095, USA ∗3Department of Systems and Control Engineering, School of Engineering, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan ∗4Honda Research Institute Japan Co., Ltd. 8-1 Honcho, Wako, Saitama 351-0114, Japan ∗5Graduate School of Fundamental Science and Engineering, Waseda University 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan

Complexity, Predictability and Time Homogeneity of Syntax in the Songs of Cassin's Vireo (Vireo cassinii).

Many species of animals deliver vocalizations in sequences presumed to be governed by internal rules, though the nature and complexity of these syntactical rules have been investigated in relatively few species. Here I present an investigation into the song syntax of fourteen male Cassin’s Vireos (Vireo cassinii), a species whose song sequences are highly temporally structured. I compare their song sequences to three candidate models of varying levels of complexity–zero-order, first-order and second-order Markov models–and employ novel methods to interpolate between these three models. A variety of analyses, including sequence simulations, Fisher’s exact tests, and model likelihood analyses, showed that the songs of this species are too complex to be described by a zero-order or first-order Markov model. The model that best fit the data was intermediate in complexity between a first- and second-order model, though I also present evidence that some transition probabilities are conditioned on up to three preceding phrases. In addition, sequences were shown to be predictable with more than 54% accuracy overall, and predictability was positively correlated with the rate of song delivery. An assessment of the time homogeneity of syntax showed that transition probabilities between phrase types are largely stable over time, but that there was some evidence for modest changes in syntax within and between breeding seasons, a finding that I interpret to represent changes in breeding stage and social context rather than irreversible, secular shifts in syntax over time. These findings constitute a valuable addition to our understanding of bird song syntax in free-living birds, and will contribute to future attempts to understand the evolutionary importance of bird song syntax in avian communication.

Sensitivity of California Thrashers (Toxostoma redivivum) to song syntax

Abstract Many birds have songs with variable structure and sequences. In earlier studies, we characterized some features from the song structures of California Thrashers (Toxostoma redivivum). In the Thrashers, there were a large number of phrase types, dozens to hundreds and the songs that were sequences of these many phrases were not random, but show some structure referred to as syntax. For example, a syntactic rule might be that phrase type A can be followed by phrase type B, but not type C. We, along with others, have assumed that syntax is an important feature of songs. This paper describes an experimental attempt to determine that syntax is important to California Thrashers by recording the reaction of territorial thrashers to playbacks of other thrasher songs, some of which obeyed the syntax rules we had discovered while others violated those rules. We also obtained video recordings of their behaviour near the playback speakers. We observed differences in the reactions to the birds that heard these two types of playbacks. Resident males reacted to either playback type, but more strongly when the original order was preserved. We observed difference in their behavioural response to correct or altered syntax. This indicates that the syntax of their songs is perceived in territorial defence by the birds.

Accounting for syntax in analyses of countersinging reveals hidden vocal dynamics in a songbird with a large repertoire

Identifying the signalling strategies employed by animals during vocal interactions is a challenge, especially for species with large vocal repertoires. We propose that efforts to study such vocal dynamics can benefit by integrating models of syntax into their analyses. In this study, we conducted playback experiments on Cassins vireo, Vireo cassinii, to examine the role of syntax, and more specifically, shared syntactic patterns, in countersinging. We presented 11 males with song sequences ordered according to population norms, and with sequences whose order deviated from population norms. We did not find evidence that individuals markedly altered their responses based on the syntax of the playback, either in their physical approach to the speaker or in the quantity of song they delivered in response. We did, however, find evidence that syntax was important in governing their choice of phrase types in response to the playbacks. Subjects did not match the playback phrase types. Instead, they engaged in a vocal behaviour referred to as song advancing, where they responded to a stimulus phrase type by singing the phrase type that most often followed the stimulus in their own normal song sequences. When playback sequences were ordered according to population norms, song advancing resulted in birds pre-empting the upcoming playback phrase type or delivering another of the prior playback phrase types (i.e. delayed matching) at higher rates than when playback sequences deviated from population norms. The detection of song advancing was only possible with the explicit inclusion of syntax in our analysis, suggesting that studies of the vocal interactions of species with repertoires of multiple vocalizations can benefit from consideration not only of a subjects repertoire, but also their syntax.

Identification of Cassin's Vireo (Vireo cassinii) individuals from their acoustic sequences using an ensemble of learners

The ability to identify individual birds can provide us with information on behavioral interactions between individuals and ecological interactions with the environment. Identifying individual animals has traditionally been a time - and cost - intensive exercise in the field. Most past efforts dedicated towards individual identification from its vocalizations have centered on the analysis of acoustic features. Here we present an alternative approach to this task, using an ensemble of learners to identify individual Cassins Vireo from the structural properties of their vocalizations, using symbolic representations of its syntactic elements instead of the acoustic characteristics of the signal. We also test the ability of this ensemble of learners to identify individuals within a year and across years. We propose a new learner combination that confers the ensemble with the ability to handle outliers - unknown individuals not seen during training. After being trained with 9 individuals from one year (2014), the ensemble achieved 96% accuracy identifying samples from 13 individual birds from the same year and 95% with sequences from 8 individual birds from a previous year. Predicting individuals in one year using recordings from other years indicates effective generalization capabilities of the ensemble.

Assessing the similarity of song-type transitions among birds: evidence for interspecies variation

In many species of songbird, individuals sing multiple song types, some of which are shared with their neighbours. Individuals may also share syntactical rules that govern the transitions between different song types, but few studies have attempted to study this kind of sharing. Progress has been inhibited by a lack of statistical tools to compare song-type transitions among individuals. We present a straightforward method for comparing song transitions based on Markov transition matrices. The method calculates the number of mutually preferred song-type-to-different-song-type transitions found in the song sequences of two birds, then assesses whether that number is significantly greater than would be expected if the two birds ordered their songs independently of one another. We applied this method to song sequences from five songbird species. All pairwise comparisons among male Cassins vireos, Vireo cassinii, showed significant similarity in song transitions, as did a minority of comparisons among Adelaides warblers, Setophaga adelaidae, and one pair of marsh wrens, Cistothorus palustris. In contrast, dyads of rock wrens, Salpinctes obsoletus, and rufous-and-white wrens, Thryophilus rufalbus, did not share song-type transitions at levels exceeding chance. Interterritory distance was not significantly related to our measure of song transition similarity in any of our study species. These results provide evidence that interindividual similarity in song-type transitions is a trait that varies considerably among species. We discuss the potential drivers of similarity in song transitions, but note that assessing its evolutionary breadth will require a larger sample of species. The application of our method to additional species will provide a more comprehensive understanding of signal use and vocal interaction in songbirds.

Detection and localization of multiple wideband intermittent acoustic sources

We have been interested in the analytical and experimental study of real-life bird song sources for several years. Bird sources are characterized by either a single or multiple bird vocalizations independent of each other or in response to others. The sources may be physically-stationary or exhibit movements and the signals are wide-band in frequency and often intermittent with pauses and possibly restarting with repeating previously used songs or with new songs. Thus, the detection, classification, and 2D or 3D localization of these birds pose challenging signal and array problems. Due to the fact that some birds can mimic other birds, time-domain waveform characterization may not be sufficient for determining the number of birds. Similarly, due to the intermittent nature of the vocalizations, data collected over a long period cannot be used naively. Thus, it is necessary to use short-time Fourier transform (STFT) to fully exploit the intricate natures of the time and frequency properties of these sources and displayed on a spectrogram. Various dominant spectral data over the relevant frames are used to form sample covariance matrices. Eigenvectors associated with the decompositions of these matrices for these spectral indices can be used to provide 2D/3D DOA estimations of the sources over different frames for intermittent sources. Proper cluttering of these data can be used to perform enhanced detection, classification, and localization of multiple bird sources. Two sets of collected bird data will be used to demonstrate these claims.