Recycle and reuse: an ethological perspective for citizen science data on Lucanus cervus (Coleoptera: Lucanidae).

Citizen science (CS) has been proven to be a powerful approach for biodiversity monitoring, offering large-scale and long-term data collection opportunities. This study explores the possibility of reusing images collected under a CS initiative aimed at mapping the distribution of the European stag beetle (Lucanus cervus [L.]) in Italy for ethological purposes. Volunteers contributed 2,090 photographic records and, among them, more than one-third were valid for ethological purposes. These records were analyzed to investigate specific behaviors, exploited substrate and seasonal preferences, considering specimen number and sex. Single males represent the majority of the sample, and the most represented couple is male-female. Regarding the ethological traits, the most recorded one is standing/walking for single specimens (both males and females) and reproductive behavior for couples. In addition, a sex-related seasonal variation has been observed with single individuals recorded mainly in July and couples in June. Moreover, substrate preferences indicated males' affinity for natural wood and females' inclination toward bare ground. However, the lack of detailed environmental cues limited additional behavioral insights. This being given, the present study underscores the possibility of leveraging volunteer-collected data from an existing CS initiative for ethological purposes, even if some limitations were encountered. For this reason, good practices are provided in order to ensure a broader applicability of ecological and behavioral research in current or future CS projects.