The Herpetological Journal

pp. 258-265

Authors: Paolo Casula, Leonardo Vignoli, Luca Luiselli & Roberta Lecis

Abstract: Visual counts gathered within citizen science programs are increasingly used to determine distribution and abundance of
species of conservation concern. However, to obtain reliable patterns from counts, imperfect detection should always be
considered, with particular reference to rare and elusive species. By analysing data from a citizen science monitoring program
based on multiple simultaneous observers, we studied detection probability of the Sardinian mountain newt, Euproctus
platycephalus. Detectability of individual newts widely varied among observers, and was positively affected by the number of
newts exposed to during sampling. Training, although appearing to improve detectability, did not accommodate for differences
among trained observers. No effect of sampling hour, tree shade, cloud cover, water flow, turbidity, and temperature was
found, possibly due to standardisation of sampling conditions. Depending on observer’s skills and the population exposed
to during sampling, detection probability of newt populations can widely vary. Most of the sampling units (pools) had few
newts exposed to during sampling, with a high probability of recording false absences. Herpetological surveys could be more
extensively based on multiple simultaneous observers to reduce observer heterogeneity bias in the detection process, and
obtain more reliable patterns of species abundance and distribution for conservation purposes.

Keywords: detection probability; Euproctus platycephalus, multiple observers, observer heterogeneity; visual counts, citizen science