Kurt Hammerschmidt

Individual Differences in Vocalisations of Young Barbary Macaques (Macaca Sylvanus): a Multi-Parametric Analysis To Identify Critical Cues in Acoustic Signalling

It had been shown that Barbary macaque (Macaca sylvanus) mothers are able to individually recognise their offspring by its vocal signals, but it remained unclear which acoustical cues may account for such an ability. In order to address this issue from a basic perspective, about 1800 calls of infants and yearlings (N = 10) were investigated. The investigation applied a method of signal analysis which allowed to determine a large number of parameters (N = 84) for each vocal signal. The application of discriminant and cluster analyses provided the following results: (1) Animals differed in almost all call parameters. However, individuals were best identified by specific parameters which formed an individually characteristic parameter set. (2) Those parameters that facilitated the assignment of vocal patterns to a given individual usually were different among individuals. (3) Infants and yearlings achieved the same maximum value of correct assignment. However, infants achieved a reasonable assignment at a much smaller number of call parameters. (4) Cluster analysis of vocalisations revealed that Barbary macaques uttered individual versions of common call types. (5) When the discriminant analysis was rerun on the call clusters, the correct assignment could be improved from 81 % to 94% for infants and from 80.5% to 96% for yearlings. Our findings suggest that Barbary macaque mothers can recognise their offspring by more than one signal cue, and such a strategy may improve the recognition systems robustness against possible distortions caused by the environment. The pronounced differences in vocal patterns of young Barbary macaques may help mothers or other group members to readily learn and recognise the individually specific signal features. The methodological procedures described in this paper provide a powerful tool for an assessment of signal parameters also in other areas of vocal interactions.

The Vocal Behavior of Barbary Macaques (Macaca Sylvanus): Call Features and Their Performance in Infants and Adults

Listening to primate vocal signals entails witnessing episodes of social significance, and students of primate social behavior are well advised to investigate such episodes, but at same time also the features of signals escorting them. Today, the study of vocal communication profits tremendously from progress in technology, which in particular allows for a parametric analysis of signal patterns and their subsequent categorization by non-subjective criteria (Beeman, 1989; Gautier and Gautier-Hion, 1988; Hammerschmidt, 1990; Hauser et al., 1993; Newman and Goedeking, 1992; Schrader and Todt, 1993). These procedures confirmed, for instance, that the concept of ‘multi-dimensional definition of call types’ is a useful tool for addressing both the composition of signal repertoires and the rules of repertoire performance or use, respectively (Hammerschmidt et al., 1994b; Owren et al., 1992). Compared to a pragmatic view describing call types as ’vocal patterns invariantly appearing in the same uniform configuration of structural properties’ (Robinson and Whitehead, 1988), the novel concept is more operational: It defines calls within a multidimensional parameter space and characterizes a particular type of call by a nucleus of significantly correlated parameter expressions within that space (Todt, 1986; Todt et al., 1992). This concept allows to investigate call type variations and also the conditions to which modifications of parameter expressions covary. Thereby, it provides a chance to address the interactional role of vocal patterns in a sophisticated manner.

Calls of the Jungle Crow (Corvus macrorhynchos s.l.) as a taxonomic character

A discriminant analysis of the call structure completely separates threeCorvus taxa (levaillantii andjaponensis of the ‘macrorhynchos group’,splendens) inhabiting the southern slopes of the Himalayas (Nepal, Kashmir). The acoustic differences are considered taxonomically relevant, indicating species boundaries. Therefore the Jungle Crows of lower and upper Nepal (contact zone at around 2,000 m) are assigned to two biospecies (C. japonensis andC. levaillantii), as is consistent with morphological, ecological and parasitological data. It appears possible to extrapolate the findings regarding call structure to the systematics of other ‘macrorhynchos’ populations as distant as the Russian Far East, and those regarding mallophagan parasites to large areas of SE Asia; regarding the vocal characteristics, however, further clarification is needed. Über die Gliederung der ostasiatischen Dickschnabelkrähen (Corvus macrorhynchos s.l.) in Biospezies besteht bisher keine einhellige Meinung. In dem großen Verbreitungsgebiet zwischen Indien, Japan und Timor werden gegenwärtig eine, zwei oder drei Arten anerkannt. Hier versuchen wir, in akustischen Merkmalen artanzeigende Merkmale zu finden. Eine Diskriminanzanalyse der Rufstruktur (76 Parameter) trennt dreiCorvus-Taxa (levaillantii undjaponensis aus der ‘macrorhynchos-Gruppe’,splendens) von der Südabdachung des Himalaya (Nepal, Kashmir) vollständig voneinander. BeiC. japonensis bleiben die trennenden Merkmale über große geographische Gebiete konstant. Die akustischen Unterschiede werden als taxonomisch relevant angesehen; sie zeigen Artgrenzen an. Folglich werden die Dickschnabelkrähen aus den Tief- und Hochlagen Nepals (Kontaktzone um 2 000 m) zwei Biospezies zugeordnet (C. japonensis undC. levaillantii), in Übereinstimmung mit morphologischen, ökologischen und parasitologischen Daten. Taxonomische Extrapolation der Befunde auf die Systematik anderer ‘macrorhynchos’-Populationen erscheint über die Rufstruktur (bis zum Fernen Osten Rußlands) und über Federling-Parasiten (Mallophaga) auf große Teile SO-Asiens möglich, bedarf aber für die stimmlichen Merkmale noch weiterer Klärung. Wahrscheinlich müssen immacrorhynchos-Komplex mindestens drei biologische Arten anerkannt werden (C. japonensis, C. levaillantii, C. macrorhynchos s. str.).

Individuelle Merkmale im „krah“-Ruf der NebelkräheCorvus corone cornix

Variation in the call type „krah“ between and within individuals was studied in seven adult Hooded Crows. 85 time, frequency, and amplitude parameters were determined for 124 calls by a specifically designed computer program (LMA 3.0) for the analysis of complex sounds. “Krah” calls were clearly individual-specific. However, individuals could be separated sufficiently from each other only on the basis of a combination of several call parameters. Using a discriminant analysis, it was possible to achieve a 100 % correct assignment of each call to the respective individual. The advantages of encoding individual specificity in more than one acoustic parameter and the possibility of encoding other information in the “krah” call are discussed. An sieben adulten Nebelkrähen wurden die Variationen des „krah“-Rufes mit Hilfe eines speziellen Computerprogamms untersucht, das 85 Rufparameter für 124 Rufe analysierte. Die „krah“-Rufe sind individual-spezifisch. Allerdings ließen sich die Individuen nur mit Hilfe einer Kombination verschiedener Rufparameter ausreichend sicher voneinander trennen. Mit einer Diskriminanzanalyse war eine 100%ig sichere Zuordnung jedes Einzelrufes zum entsprechenden Individuum möglich.