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Individual variation in vocalizations has been widely studied among different animal taxa, and it is commonly reported that vocalizations could be potentially used to monitor individuals in many species. Songbirds represent a challenging group of animals for the study of signalling of individual identity. They are highly vocal, but their songs are complex and can change over time. In this study, we tested whether general song characteristics, which are independent of song type, can be used to discriminate and consistently identify Chiffchaff males within and between days and between years. There was individual variation in songs of recorded Chiffchaffs, and it was possible to easily discriminate between males at any one point in time. However, the level of re-identification of males across days and years was low. For effective identification it was necessary to compare songs of a single song type. However, Chiffchaffs haphazardly switch among song types, sometimes singing the same song type for a long time, making it difficult to collect equivalent song types or to sample the birds' full repertoires. For example, 5-min recordings of males taken in different years did not contain equivalent song types, leading to low identification success. Although we were not successful in the re-identification of males based on general song characteristics, we discuss methods of acoustic identification which are not dependent on song repertoire content and are potentially valuable tools for the study of species such as the Chiffchaff.

The ability of individuals to recognize others based on vocalizations has been proven in many species of birds. However, we are still far from understanding important aspects of the discrimination process. For example, it is still not fully understood whether, and why, repertoire size hinders discrimination between individuals. Further, the strategies and vocal cues used for discrimination between individuals are largely unexplored. In this study, we tested the ability of chiffchaffs Phylloscopus collybita and willow warblers Phylloscopus trochilus, two closely related species with different repertoire sizes and song organization, to differentiate between their neighbours on the basis of a single song of a neighbouring male. We did playback experiments within the 'dear enemy' paradigm in which we tested resident males with a single song of a neighbour broadcast from the correct and opposite, incorrect territory border. Both species displayed a strong ability to discriminate between their neighbours representing further evidence that repertoire size per se has no negative impact on individual recognition in songbirds. Using a single song for playback allowed us to speculate about the nature of the possible cues used by males for recognition. Individual recognition in both species is most likely based on the modulation of syllables or on general voice characteristics. We suggest that specific changes in song organization, for example the tendency of individuals to insert a distinct phrase at the beginning of each song, may facilitate individual recognition and compensate for increased repertoire size in willow warblers.

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In total, 616 reliable records (C1, C2 category sensu SCALP) of wildcat occurrence in Bohemia were collected and analysed in 11 monitoring seasons, “wildcat years” (WCY), 2010–2021. Camera-trapping data accounted for 95% of the dataset, the rest of the records were verified by the genetic analysis of several hair samples, scats, and tissue samples. The occurrence of the European wildcat was confirmed in eight sub-areas, more continuously in the forested border areas of southern and western Bohemia, and more sparsely in central and northern Bohemia. In total, the wildcat occurred at 73 different sites, in 35 mapping squares: four confirmed as category C1, 31 as category C2. The current occurrence in the western part of the Czech Republic is linked to that in neighbouring Germany. The development of modern non-invasive monitoring methods was crucial for the increase in detection of wildcat presence. However, both reintroduction and population increase in Bavaria and climactic change can also play a role as drivers of the recent spreading of the wildcat to our territory. Reproduction was confirmed in two sub-areas (Český les Mts., WCY 2021; Doupovské hory Mts., WCY 2020) and represents the first documented reproduction of the wildcat in Bohemia since the WWII. In some large areas such as the Šumava Mts., we observed a rather wider spatial activity, smaller numbers of individuals and more transient character of occurrence than in other (more restricted) areas, such as the Doupovské hory Mts., where we found higher population density and permanent occurrence with reproduction. Species-specific systematic camera-trapping and genetic monitoring in all areas with confirmed occurrence is highly recommended for the future.