Body condition is increasingly used to assess the status of populations and as a proxy for individual fitness. A common, quick and non-invasive approach is to estimate condition from the relation between body length and mass. Among the methods developed for this purpose, the Scaled Mass Index (SMI) appears best suited for comparisons among populations. We assembled data from 17 populations of European green toads (Bufotes viridis) with the aim of devising a standard formula applicable for monitoring this species. The mean value of the exponents describing length–mass allometry in these samples was 3.0047. Hence, we propose using 3 as a scaling coefficient for calculating the SMI in green toads. From the contrast of SMI values for both sexes within populations, estimated with either the population-specific or the standard coefficient, we conclude that applying the standard formula not only facilitates comparisons among populations but may also help to avoid misinterpretation of variation within populations.

Background Sex ratios of animal populations are important factors of population demographics. In pond-breeding amphibians, the operational sex ratio (OSR) among the breeding population is usually male-biased. Also, in European green toads (Bufotes viridis), males usually outnumber females at breeding sites, while the sex ratio of the total adult population (ASR) is assumed to be balanced. It has been suggested that sex-specific breeding behavior causes male-predominance at the breeding sites. We used a dataset of 5 years of street patrols to test this hypothesis. For this we analyzed local sex ratios of green toads in terrestrial habitats and at two artificial breeding ponds. We expected temporal and/or spatial changes of local sex ratios which would indicate sex dependent differences in breeding behavior. Results Overall observed ASR among 2111 green toads, counted in the course of street patrols from 2016 to 2020, was slightly male-biased (ASR = 0.56, annual ASRs = 0.49–0.63). Based on the data of 1631 toads (920 males, 711 females) captured within a radius of 300 m around nine main breeding sites, temporal and spatial variations in local ASRs were evaluated. Resulting values were compared to the calculated OSR at two artificial breeding ponds in 2021 (645 adult: 553 males, 92 females). Estimates predict more equally distributed females and males prior to the main breeding season. During breeding season, males predominated at both breeding sites (B1: 0.83, B2: 0.89), whereas females are estimated to outnumber males in terrestrial habitats. Proportions of females highly significantly increased with advancing time of the year and increasing distance to the breeding sites. While males tended to accumulate in proximity to water bodies, females dispersed soon after breeding to more distant areas. Conclusions Observed sex ratios in the studied green toad population changed with time and sampling site, deviating from the population-wide sex ratio. Expanding sampling effort in amphibian conservation assessments in time and space, i.e., outside the main breeding season and away from the breeding sites, would be important to encompass such variations.