Snakes and the Eternal City: variation in community metrics, body size and population density of snakes in contrasted landscapes of suburban Rome (Italy)

Reports of global declines in animal populations are now numerous and also include snakes, a group of animals now widely regarded as bio indicators. A prerequisite for any conservation management plan to protect or restore snake populations requires a data base that provides insight into population composition and changes. However, snakes are well known to be particularly difficult to quantitatively sample due to their secretive and elusive nature, and hence accumulating an adequate database for analysis requires long-term field studies that involve intensive searches. Populations of four snake species, Zamensis longissimus, Natrix helvetica, Vipera aspis and Hierophis viridiflavus living in two suburban areas of Rome with different extents of habitat alteration (deforestation), Vejo, a less altered site, and Tor Bella Monaca, a high altered site, have been monitored, but with interruptions since 1995. The results indicated that H. viridiflavus was the commonest species at both sites. Male bias was found in all four species but especially in Z. longissimus and V. aspis with detection of juveniles greatest in H. viridiflavus and N. helvetica. Snout to vent lengths (SVL) of H. viridiflavus and Z. longissimus, which were present at both sites, were greater at the less degraded habitat of the two study localities. Community metrics indicated that the degraded habitat had lower species richness, evenness, Shannon and Simpson diversity indices, but a higher dominance index. Recapture frequencies of snakes recaptured either once or multiple times were in general greater at Vejo. The highest population densities were found in H. viridiflavus, followed by V. aspis and N. helvetica, which were similar. However, long term trends in densities show declines in V. aspis and N. helvetica between 1995 and 2019. Population densities were in good agreement with density estimates found in previous studies of snakes in more natural habitats.