THE LINE TRANSECT METHOD FOR ESTIMATING DENSITIES OF LARGE MAMMALS INA TROPICAL DECIDUOUS FOREST - AN EVALUATION OF MODELS AND FIELD EXPERIMENTS

We have evaluated techniques of estimating animal density through dire ct counts using line transects during 1988-92 in the tropical deciduou s forests of Mudumalai Sanctuary in southern India for four species of large herbivorous mammals, namely, chital (Axis axis), sambar (Cervus unicolor), Asian elephant (Elephas maximus) and gaur (Bos gauras). De nsity estimates derived from the Fourier Series and the Half-Normal mo dels consistently had the lowest coefficient of variation. These two m odels also generated similar mean density estimates. For the Fourier S eries estimator, appropriate cut-off widths for analysing line transec t data for the four species are suggested. Grouping data into various distance classes did not produce any appreciable differences in estima tes of mean density or their variances, although model fit is generall y better when data are placed in fewer groups. The sampling effort nee ded to achieve a desired precision (coefficient of variation) in the d ensity estimate is derived. A sampling effort of 800 km of transects r eturned a 10% coefficient of variation on estimate for chital; for the other species a higher effort was needed to achieve this level of pre cision. There was no statistically significant relationship between de tectability of a group and the size of the group for any species. Dens ity estimates along roads were generally significantly different from those in the interior af the forest, indicating that road-side counts may not be appropriate for most species.