Effects of disturbance, position of observer, and moonlight on efficiency of anuran call surveys

Anuran call surveys are being used widely to monitor amphibian populations and study amphibian declines. To help optimize call surveys, we studied several factors that potentially affect the efficiency of this method. We studied whether the approach of observers to the listening site potentially disturbs calling amphibians and whether disturbance is reduced after 5 min using 230 roadside call surveys along 23 routes. On each route, listening time for five of ten sites was 5 min; listening time for the other five surveys on a route was 10 min. We detected nine species in these surveys. We found no significant difference in the number of species heard in the first 5 min of a 10-min survey compared to the second 5 min, nor a significant difference in the number of species heard when comparing 5-min surveys and the second 5 min of 10-min surveys. These results suggest that there is no detectable disturbance upon approach, or if disturbance occurs it does not dissipate after 5 min. The effect of the observer's listening orientation on number of species heard was examined in 110 roadside call surveys along 11 routes. Changing orientation during the call survey did not increase the number of species heard. Significantly greater numbers of species were detected during surveys conducted under low moonlight.