Bird vocalizations during spring migration on a small Mediterranean island (Ventotene, Italy)

Ventotene Island, a small Mediterranean island off the Latium coast (Central Italy), is an important stopover site for several migratory bird species. The migration pathways of these species have been largely studied with classical approaches, such as bird ringing activities, bio-logging, isotope studies, and radar networks. The latest methodological approaches involve bioacoustics analyses (i.e. sonogram analyses), making advantage of the availability of new low-cost ARUs (Autonomous Recording Units) technology. However, although bird species are known to emit breeding and non-breeding vocalizations during migrations, scientific knowledge on these vocalizations is still scarce, particularly in insular stop-over areas. In this study, 54 field surveys were carried out on Ventotene Island during the early spring migration season (April 2024), following a recording protocol of 10-min per sample-point on different day-hours. Three surveys were carried out for each sample-point, resulting in a total of 540 minutes (9 hours) of audio-recording. The vocalizations of the bird species were identified through acoustic and visual sonogram analyses and categorized by their structural similarity. A total of 19 bird species were identified from the audio-recordings. Among them, Eurasian Collared Dove (Streptopelia decaocto), European Serin (Serinus serinus), Sardinian Warbler (Curruca melanocephala), Collared Flycatcher (Ficedula albicollis) were the most frequently contacted. The majority of bird vocalizations consisted of alarm and social calls, while reproductive songs were recorded for nine species: Eurasian Collared Dove, Common Cuckoo (Cuculus canorus), Eurasian Blackbird (Turdus merula), Common Nightingale (Luscinia megarhynchos), Great Reed Warbler (Acrocephalus arundinaceus), Common Whitethroat (C. communis), Sardinian Warbler, European Serin, Western Yellow Wagtail (Motacilla flava). The results of this study highlight the potential of bioacoustics as a promising and non-invasive tool for detecting the presence of both migratory and sedentary bird species during spring migration. However, future research should aim to refine recording protocols and field survey techniques, as well as compare the effectiveness of bioacoustics monitoring with other established methods.