Reliable estimates of status and population trends are critical for the conservation of large terrestrial carnivores. Camera trapping technique have been widely used for population estimation of cryptic carnivores including tigers, but the issues regarding sampling design and effort required to effectively sample an area have been paid less attention.

A total sampling effort of 462 trap nights yielded 50 photo-captures of 12 individual tigers over 14 sampling occasions that effectively covered a 111-km2 area. The model M(o) fitted the capture history data well. The estimated capture probability/sample, p-hat = 0.22, resulted in an estimated population size and standard error (N(SE N)) of 12 (0.65), and a density (D(SE D)) of 10.81 (1.43)/100 km2.  

Camera spacing was found to considerably influence the population estimation. An increase in camera spacing from 1.5 to 2.5 km resulted in a loss of 35% (n=7) of photo captures which consequently decreased the precision of the estimates, though accuracy was not affected. A reduction in the trapping effort in terms of reduced trap nights resulted in lower level of precision though the accuracy of estimates was not affected.

Increase in the camera spacing from 1 to 2 km with a decrease in the number of sampling occasions (six) resulted in the loss of 42% of photo captures (n=12) and loss of 25% of individual tigers ((Mt+1=9) thus underestimating the true tiger population by 16% ((N(SE N)) being 10(1.84)

The different statistical estimators viz., capture-recapture and jackknife did not show significant differences in the population estimation. The differences between the density estimates generated by “camera trapping” (D=10.81/100 km2, S.E.=1.43) and “intensive search effort” (D=11.76/100 km2, S.E.=0.65) for tigers were not significantly different. My results suggest that “intensive search effort” for tigers if used within capture-recapture framework can be used to arrive at reliable population estimates.

M. Sc. Dissertation :
Evaluating tiger (Panthera tigris) population estimation approaches   in a high density area in Kanha Tiger Reserve– Rishi Kumar Sharma

Rishi Kumar Sharma, M.Sc.