Demographic monitoring of the invasive ladder snake on Formentera (Balearic Islands, Spain)

Abstract The ladder snake Zamenis scalaris was first reported in 2006 Formentera (Balearic Islands, Spain), until then a snake‐free Mediterranean island. Since 2016, intense control campaigns have been carried out and, for the time, captures over 2017–2020 used to analyze sex ratio, age, fat percentage, population density, and seasonality of this invasive population. male‐biased ratio found present work could be result capture biases caused by different detection probabilities between sexes. A reduction body length time observed, which indicate depletion larger snakes due capture. highest frequencies both sexes were May June, coinciding with mate searching period species native range indicating that increase their movements during period. Size‐specific survivorship curves indicated drop at medium sizes, suggested survival cost associated reproduction, presumably increased mortality mating season. Population density decreased from 1.812 snakes/ha 2017 0.669 2020. Evidence obtained has allowed evaluate main ecological aspects Z. current state on island Formentera. Results showed is well established Formentera, but prolonged its decline. This study becomes starting point improve management programs populations Balearic Islands. Long‐term as improvement adult females are strongly recommended attempt eradication