Ecologists endeavour to develop survey techniques that are cost-effective for the species they target and robust enough for statistical analysis. Using time as a measure of effort, we compared visual encounter surveys with artificial cover objects (strapped to trees), targeting an arboreal elapid, the pale-headed snake (Hoplocephalus bitorquatus) and its potential prey (geckos). Within a red gum forest vegetation community with relatively high snake density, capture rates were 0.6 0.1 (s.e.) snakes/person-hour using visual encounter surveys, compared with only 0.1 0.1 snakes/person-hour using cover objects. The probability of detection of pale-headed snakes was estimated from occupancy modelling at 0.70 0.06 in visual encounter surveys and 0.19 0.09 in cover object surveys. Gecko capture rates (among all vegetation communities) were significantly greater (P < 0.001) using cover objects. The probability of detection of geckos was estimated from occupancy modelling at 0.77 0.05 in visual encounter surveys and 0.97 0.02 in cover object surveys. Geckos favoured (P < 0.001) cover objects facing south during all seasons except winter. Artificial cover objects may provide some value in detecting pale-headed snakes in vegetation communities where habitat resources are limited however, where resources are plentiful, visual encounter surveys are likely to remain the most cost-effective survey option.
Australian Journal of Zoology – CSIRO Publishing
Published: May 12, 2021