J. H. K. PECHMANN, D. E. SCOTT, R. D. SEMLITSCH, J. P. CALDWELL, L. J. VITT, J. W. GIBBONS,
Declining Amphibian Populations: The Problem of Separating Human Impacts from Natural Fluctuations Science. ,vol. 253, pp. 892- 895 ,(1991) ,
10.1126/SCIENCE.253.5022.892