Justification:
Most Bengal Tigers are found in India, which has recently revamped its national tiger census methodology to be more scientific, extrapolating site-specific densities derived from camera trap and sign surveys using GIS. The 2010 survey resulted in an estimated population of 1,706 (1,520–1,909) (Jhala et al. 2011), an increase from 1,411 in 2006 (Jhala et al. 2008). The increase is in part due to inclusion of new areas in the most recent survey (Sunderbans, some portions of North East and parts of Maharashtra), but tiger densities were found to have increased in areas of Uttarakhand, Tamil Nadu, Maharashtra and Karnataka. However, the survey found a decrease in tiger range of 12.6% in connecting habitat corridors from 2006–2010 (Jhala et al. 2011).
Other Bengal Tiger population estimates from national governments for the Global Tiger Recovery Program include Bangladesh (440), Nepal (155) and Bhutan (75). The total subspecies population is estimated at fewer than 2,500 tigers (2,376). No subpopulation is larger than 250. There has been a continuing decline over the past three tiger generations (20–30 years). The previous national India tiger census result of 3,642 in 2001–2002 cannot be directly compared to more recent surveys, as a different and somewhat discredited methodology was employed (attempting to identify individual tigers on the basis of unique pugmarks, or tracks). Nonetheless, a substantial decline in India's Tiger population is suggested.
Sanderson et al. (2006) built upon previous work by Dinerstein et al. (1997) to map priority landscapes for tigers (Tiger Conservation Landscapes). The Tiger's extent of occupied area is estimated at less than 1,184,911 km² (Sanderson et al. 2006), a 41% decline from the area estimated by Dinerstein et al. (1997). India suffered the most range contraction. While part of the difference is due to improved data after a decade of intensive tiger conservation efforts, and improved datasets and techniques, biologists consider the primary cause to be declines due to poaching and habitat loss (Dinerstein et al. 2007). Range decline is considered a strong indicator of population decline (Dinerstein et al. 2007). Because an average of 55% of Tiger Conservation Landscapes consist of non-tiger habitat (Sanderson et al. 2006), the declines in population and area of occupancy are greater than the 41% estimated, and thus likely indicate a 50% or greater reduction. A similar reduction could be expected over the next three tiger generations (20–30 years) unless conservation effort becomes more effective.
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Decreasing
