Persistent Winter Activity in Triturus ivanbureschi Arntzen & Wielstra, 2013 (Amphibia: Caudata).

Most amphibians from the temperate climate zones hibernate during the winter, and although incidental observations of winter activity are not rare, systematic data are still lacking. The study was conducted throughout the astronomical winter (December 2020 -- March 2021) in a pond near Sofia, Bulgaria. Funnel traps were set each week for the duration of the study and the ventral side of all captured newts was photographed to allow for individual identification. The following parameters were measured: dissolved oxygen in the water, air and water temperature. Results demonstrated that both male and female newts were active in the water throughout the winter period, even when the surface of the pond was frozen solid (at times, the ice was thick enough for a human to safely walk on the pond). As early as the beginning of January, males had very prominently developed crests. A total of 153 individual newts were captured, with 79 (51.63 %) of them recaptured at least once. Recaptures were used to calculate the maximum active population size, which was 142±9 (125-159) for males and 94±13 (69-118) for females. The number of captured newts each session correlated very closely with estimated active population size but there was no apparent correlation with the values of the measured parameters. [ABSTRACT FROM AUTHOR]