Counts of calling males as estimates of population size in the endangered frogs Geocrinia alba and G. vitellina

The ability to estimate the size of populations is an integral part of species conservation. I investigated the utility of counts of calling males for the rapid and efficient assessment of population size in the endangered frogs Geocrinia alba and G. vitellina from southwestern Australia. Multiple censuses were used to examine the optimum time of night and season to conduct surveys. Turnover of calling males was measured using removal and mark-recapture studies. Males called persistently throughout the night, but the time of the annual peak in the number of calling males varied among sites. Turnover of males was very low, with the majority of males in each population (76-96%) calling simultaneously. Combining knowledge of the sex ratio with counts of calling males, it is therefore possible to obtain a good estimate of total population size.