Try link to:Similars in:
Crump, M.L. & N.J. Scott Jr. 1994. Visual Encounter Surveys, p. 84-92. In W.R. Heyer, M.A. Donnelly, R.W. McDiarmid, L.C. Hayek & M.S. Foster (eds.). Measuring and Monitoring Biological Diversity, Standard Methods for Amphibians. Smithsonian Institution, Washington D. C, USA.