Long-term fidelity to communal oviposition sites in Hierophis viridiflavus

A communal oviposition site of western whip snakes, Hierophis viridiflavus, was surveyed every June for 13 years (1990–1997; 2001–2005) at a hilly locality of central Italy (Oriolo Romano, province of Viterbo, about 400 m a.s.l.). The snakes were individually marked, and hence the individual histories of several specimens were assessed over more than one year. The oviposition site was a partially dilapidated building with stony boxes, surrounded by spiny shrubs. Overall, at the study site, 41 gravid females were captured over 13 years of study, together with five adult males and 189 newborn snakes. No non-gravid females were found. Hence, it seems that the study site is used by snakes solely for egg-laying. In total, 73 oviposition events occurred in the study area, and on average the study area was visited annually by 5.46±1.05 gravid females (range 4–7). Gravid females visited the study area for periods of 2.20±1.38 years (range1–5 years); some individuals visited the study site in consecutive (up to three) years, others in alternate (up to five) years, and others at irregular intervals (up to four years). The communal oviposition site was not used preferentially by any specific size category of snakes, but every gravid female in the population, from those presumably young (around 110 cm in length or less) to those presumably old (longer than 120 cm) appeared to use it regularly for laying eggs. There was an effect of year on snake clutch size, but not on the mean body size of snakes. The criteria used by snakes for the selection of the study area as an oviposition site were 1) safe conditions, due to a scarcity of natural predators, and 2) adequate conditions for egg development in a area with resource scarcity for adequate oviposition sites for snakes.