IUCN / SSC Cat Specialist Group - Digital Cat Library |
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| Karanth, K.U.; Gopalaswamy, A.M.; Kumar, N.S.; Delampady, M.; Nichols, J.D.; Seidensticker, J.; Noon, B.R.; Pimm, S.L. | |
| Counting India's Wild Tigers Reliably | |
| 2011 Science (332): 791-792 | |
The Indian government reported a 16% increase in tiger numbers over the past 4 years (News of the Week, Around the World item "Tiger numbers up? Maybe," 1 April, p. 18). This implies an average increase of 49% in local tiger densities, despite the reported range contraction of 22%. Yet these assertions cannot be verifi ed because details of tiger photo-captures at sampled locations, as well as of spatial extrapolations from these data, are incomplete (1-3). Reported tiger numbers were based on calibrations of tiger sign encounter rates against estimated local tiger densities (2), but the recently released values of correlation coeffi cients were much higher than have been reported previously (4, 5). Moreover, the extrapolation of tiger numbers to wider regions is reportedly based on standard methods of sampling and estimation (1), but it is not clear from reports (1-3) whether the survey protocols used actually match these standard practices (6, 7). A recent global analysis (8) showed that 70% of wild tigers survive in 42 "source populations" that occupy a mere 6% of remaining habitat. Although such source populations may suffer annual losses of more than 20%, studies of tiger population dynamics show that high recruitment rates compensate for these losses when there is adequate prey and protection (9, 10). Therefore, future efforts to reverse tiger declines must focus on reliably monitoring tiger numbers, as well as survival and recruitment rates, in these threatened source populations. There is a scientifi c consensus that monitoring should be conducted annually-within 30 to 45 days to avoid population fl uctuations-and cover an area of more than 500 km2, at intensities of more than 500 trap-nights per 100 km2 (11). The monitoring protocol for India's national animal requires a major overhaul if it is to generate transparent, reliable measures of tiger conservation successes (or failures) in the future. |
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