Master's Defensio


Amir Sistani BSc

The European Green Toad (Bufotes viridis) in Donaufeld (Vienna, Austria): status and size of the population.

Advisor: Günter Gollmann

Master's Defensio - Wednesday, April 14th 2021


The European Green Toad, Bufotes viridis (Laurenti, 1768) is a species with endangered populations, in Austria it is considered as vulnerable and in Vienna as critically endangered. This capture-recapture study aimed to assess the status and size of the population of B. viridis in the Donaufeld (Vienna, Austria). Over the course of this study, 79 individuals (66 males, 10 females, 3 juveniles) were captured. On each occasion the Body Mass (BM) and Snout-Vent-Length (SVL) of the captured toads as well as the sex were recorded. Additionally, a photo of the unique dorsal pattern of each captured individual was taken. For assessing the condition of the toads, the Fulton-Index was calculated, separately for each occasion. To identify the individuals, the program HotSpotter was used, an image recognition software. For the population-assessment a capture-recapture model in R was built by applying Jolly-Seber-Schwarz-Arnason (JSSA) models, using the package openCR. The estimated population-size was 113 individuals, with a confidence interval reaching from 86 to 144. Furthermore, the development of tadpoles to toadlets (metamorphlings) was verified at the identified spawning-ground, documenting reproductive success. Additionally, syntopy of the Green Toad and the Common Toad (Bufo bufo) was observed, even a rare mismatch-mating between the two species.