Pavel Linhart

Automatic recognition of bird individuals on an open set using as-is recordings

Abstract The most common method used to determine the identity of an individual bird is the capture-mark-recapture technique. The method has several major disadvantages, e.g. some species are difficult to capture/recapture and the capturing process itself may cause significant stress in animals leading even to injuries of more vulnerable species. Some studies introduce systems based on methods used for human identification. An automatic system for recognition of bird individuals (ASRBI) described in this article is based on a Gaussian mixture model (GMM) and a universal background model (GMM-UBM) method extended by an advanced voice activity detection (VAD) algorithm. It is focused on recognizing the bird individuals on an open set, i.e. any number of unknown birds may appear anytime during the identification process as is common in nature. The introduced ASRBI processes the recordings just as if they were recorded by an ornithologist: with durations from seconds to minutes, containing noise and unwanted sounds, as well as masking of the singer, etc. Thanks to the VAD algorithm, the proposed system is fully automatic, no manual pre-processing of recordings is needed, neither by cutting off the songs nor syllables. The overall achieved identification accuracy is 78.5%, the lowest 60.3% and the highest 95.7%. In total, 90% of all experiments reach at least 70% accuracy. The result suggests the application of the GMM-UBM with VAD is feasible for individual identification on the open set processing real-life recordings. The described method is capable of reducing both the time consumption and human intervention in animal monitoring projects.

Song pitch indicates body size and correlates with males' response to playback in a songbird

The inverse relationship between body size and vocalization pitch has been described in a number of species. Nevertheless, the existence of size–pitch allometry within any songbird species is surprising due to the small size variation between males, the determinate growth and exceptional vocal prowess of the taxon. The phenomenon has been documented in only a few songbird species so far and the consequences of allometry remain unclear in this taxonomic group. In this study, we provide evidence that song spectral features are related to one of the body size components (tarsus length) even in a very small songbird species: the willow warbler, Phylloscopus trochilus. Moreover, the response of territorial males was affected by the pitch asymmetry between the subject and the playback stimulus: the lower-pitched the subjects song in respect to the stimulus the bolder was its response. Our results suggest that willow warbler males may use song pitch to assess the body size of their rivals (i.e. their fighting ability) in male–male competition for resources.

Structure and Complexity of Perched and Flight Songs of the Tree Pipit (Anthus trivialis)

We analysed 2166 songs of 90 males of the tree pipit (Anthus trivialis; Passeriformes: Motacillidae) from five Czech localities to evaluate variation in song characteristics, the song structure and syntax rules, and differences between songs performed in flight and from perches. We measured temporal and spectral song characteristics; structure analysis was based on the identification of individual syllable units. There was a high among-population variation in the repertoire, suggesting substantial differences in local dialects. Flight and perched songs significantly differed in most analysed quantitative characteristics. While both types of songs are apparently used in territorial defence, trill elements within flight songs may also indicate male quality to potential mates. Characteristic bi-syllable repeats within songs were often unique for individual males and may function in individual recognition. Features of tree pipit songs make it a good species for studying song variation and function in birds with complex repertoires.

Correction: The assessment of biases in the acoustic discrimination of individuals

[This corrects the article DOI: 10.1371/journal.pone.0177206.].

Correction to: Cues to individual identity in songs of songbirds: testing general song characteristics in Chiffchaffs Phylloscopus collybita

In the original publication of this article, the Acknowledgements section is mentioned as.