Snakes among citizens: distribution and ecology of the Aesculapian snake, Zamenis longissimus (Laurenti, 1768) in Bratislava revealed by citizen science.

BACKGROUND: Urban environments are increasingly recognized as important habitats for wildlife, yet information on how reptiles use urban environments remains scarce. The Aesculapian snake (Zamenis longissimus), a non-venomous colubrid widespread in Central Europe, is considered a habitat generalist with a frequent association with human settlements. However, data on its occurrence and ecology in metropolitan areas are limited. To address this gap, we implemented a citizen science initiative in Bratislava, Slovakia, aiming to document the distribution and habitat use of the Aesculapian snake and to evaluate the potential and limitations of citizen science for reptile monitoring in urban environments.

RESULTS: Between April 2019 and October 2022, a citizen science initiative was implemented to monitor the distribution and ecology of the Aesculapian snake in Bratislava, Slovakia. The project relied primarily on social media, which proved to be the most effective channel for data collection, complemented by direct e-mail submissions. Altogether, volunteers provided 588 verified records of the focal species, alongside 184 misidentified observations of other native reptiles, most frequently Natrix spp. Spatial analyses showed that most observations of the Aesculapian snake in Bratislava were concentrated in natural and semi-natural areas at lower elevations below 300 m a.s.l., with a few records above 500 m. Within these areas, snakes were most often reported from built-up and forested land cover, while agricultural land yielded comparatively few sightings. Seasonal patterns indicated a pronounced peak in spring and early summer, while diurnal activity was dominated by midday and afternoon observations. Specifically, the number of reports declined with increasing urbanization intensity but was higher in more densely populated areas, reflecting both ecological patterns and the availability of observers.

CONCLUSION: This study delivers one of the most comprehensive datasets on the Aesculapian snake in an urban setting, highlighting its synanthropic behavior and frequent use of anthropogenic habitats. At the same time, the results underscore both the opportunities and inherent biases of citizen science, confirming its value as a complementary tool for monitoring reptile populations in metropolitan environments.