Chorus tenure and estimates of population size of male European tree frogs Hyla arborea: implications for conservation

Chorusing male anurans typically spend only a part of the breeding season calling although chorus tenure is often the best predictor of mating success. We determined the number of nights males attended a chorus (chorus tenure) and its influence on mating success in the European tree frog, Hyla arborea. The median chorus tenure was 7.5 nights out of a study season of 38 nights. Males that spent more than two nights in the chorus were present for an average of 47% of the nights between their first and last night in the chorus. Minimum daily temperature, ambient temperature at initiation of calling, and daily rainfall explained 37.8% of the variance in male attendance. Twenty-five males were calling on the night of peak activity, a fraction of the 44 males marked. This suggests that estimates of male population size based on peak activity, widely used by conservation biologists, are inaccurate. We suggest that, when mark-recapture methods cannot be used, male population size be calculated by using a regression model based on the peak number of calling males that can be further developed as more data accumulates.