Abstract
Animals—including conservation biologists—use acoustic signals to recognise and track individuals. The majority of research on this phenomenon has focused on sounds generated by vocal organs (e.g., larynx or syrinx). However, animals also produce sounds using other parts of the body, such as the wings, tail, legs, or bill. In this study we focused on non-syrinx vocalisation of the great spotted woodpecker, called drumming. Drumming consists of strokes of a bill on a tree in short, repeated series, and is performed by both males and females to attract mates and deter rivals. Here, we considered whether the great spotted woodpecker’s drumming patterns are sex-specific and whether they enable individual identification. We recorded drumming of 41 great spotted woodpeckers (26 males, 9 females, 6 unsexed). An automatic method was used to measure the intervals between succeeding strokes and to count strokes within a drumming roll. The temporal parameters of drumming that were analysed here had lower within- than between-individual coefficients of variation. Discriminant function analyses correctly assigned 70–88% of rolls to the originating individual, but this depended on whether all individuals were analysed together or split into males and females. We found slight, but significant, differences between males and females in the length of intervals between strokes—males drummed faster than females—but no difference in the number of strokes within a roll. Our study revealed that temporal patterns of drumming in the great spotted woodpecker cannot be used for unambiguous sex determination. Instead, discrimination among individuals may be possible based on the intervals between strokes and the number of strokes within a roll. Therefore, it is possible that differences in the temporal parameters of drumming may be used by birds to identify each other, as well as by researchers to aid in census and monitoring tasks.
Highlights
Vocal individuality is usually considered in one of two contexts: practical—when biologists and ecologists utilise acoustic features to identify individuals [1], and biological—when animals use unique characteristics of vocalisation to identify each other [2,3]
In our study we focused on vocal individuality in non-syrinx vocalisations of the great spotted woodpecker (Dendrocopos major)
SSD3 and SSD4 were excluded from discriminant function analyses (DFAs) (r > 0.8)
Summary
Vocal individuality is usually considered in one of two contexts: practical—when biologists and ecologists utilise acoustic features to identify individuals [1], and biological—when animals use unique characteristics of vocalisation to identify each other [2,3]. Regardless of the context, two terms should be clearly distinguished when vocal individuality is considered: discrimination and identification [1]. Discrimination addresses only the question of whether observations are being made on different individuals or not necessarily on different (i.e. different or the same). Discrimination means that animals are able to classify a particular individual as belonging to a specific class or group. Territorial skylarks (Alauda arvensis) discriminate individuals as belonging to one of two categories: their familiar neighbours or unfamiliar stranger birds [3]. Ravens (Corvus corax), on the other hand, are able to discriminate familiar group members from unfamiliar individuals even after a long period of separation [5]
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