Razorbills Alca torda in Italian Seas: A Massive Irruption of Historical Relevance and Role of Social Network Monitoring

SIMPLE SUMMARY: Razorbills Alca torda are usually found in cold, northern waters, but hundreds of them have been detected underfed in Italy in November–December 2022. Occasional irruptions of these boreal seabirds have been documented in Italy, but poor information is available on this phenomenon. Social media (including social networks and citizen-science platforms) has allowed us to track the razorbill irruption of 2022 in detail and, in this work, we assessed the distribution of records throughout the central and the southern Mediterranean country coastlines. We collected over 250 records of this species, all of them in the western and southern Italian coasts, with some records from Malta and Maghreb and with the first record for this species in western Greece. Our work emphasizes the importance of social media, which allowed us to collect about 40% of records, to depict reliable distribution maps of rare and accidental species, attracting wildlife enthusiasts and naturalist-photographers. ABSTRACT: Reporting on uncommon wide animal movements could help in depicting potential carry-over effects at the population level, particularly in an era of rapid climate and environmental changes. The razorbill (Alca torda, Linnaeus 1758) is a regular passage migrant and winter visitor to Italian seas, but with sporadic presences usually involving small numbers of individuals. Irruptions have been occasionally documented, with the last records of an unusually large number dating back to 1982. However, in the past, irruptions have only been locally reported and poorly described. Here we report on an unprecedented massive irruption of hundreds of razorbills which occurred in the central Mediterranean Sea in November-December 2022. Using citizen science platforms and photos/videos shared on social networking sites (SNSs), we estimated the relative magnitude of the irruption and described the spatial distribution of birds at sea, as well as report cases of stranded individuals. We collected a total of 267 records, both from Italy and from neighboring countries. We also discuss the likely factors affecting razorbill irruption and stress the importance of open social platforms and data sharing to aid in the early detection and estimation of such events at a wide-scale, as well as for the monitoring of the mortality of the irrupted species.