Research Article: Karanth, K. U., Gopalaswamy, A. M., Kumar, N. S., Vaidyanathan, S., Nichols, J. D., & MacKenzie, D. I. (2011). Monitoring carnivore populations at the landscape scale: occupancy modelling of tigers from sign surveys. Journal of Applied Ecology, 48(4), 1048-1056. https://doi.org/10.1111/j.1365-2664.2011.02002.x

Blog Author: Aditya Banerjee

Key highlights:

  • Monitoring tiger populations in fragmented habitats requires assessing their presence on a landscape scale by looking for indirect signs such as pugmarks or feces.
  • Such efforts often face challenges of incomplete detection, as tiger signs can be missed, and not finding any signs doesn’t always mean tigers are truly absent.
  • In 2006-07, scientists visited the same sites multiple times to make sure they did not miss tiger signs. This method helps correct errors that happen when signs are overlooked.
    • Using this approach in Karnataka’s Malenad-Mysore Tiger Landscape (MMTL), tigers were found in about 66% of sites, compared to only 47% when missed signs weren’t considered.
  • The main factors influencing tiger presence and detection were the amount of suitable forest habitat, the availability of prey, and the level of livestock presence (as a sign of human disturbance).

The Bengal tiger (Panthera tigris tigris), India’s national animal, continues to face challenges despite official censuses showing signs of recovery. Much of its habitat is fragmented, with only a few patches supporting stable populations. Understanding where tigers persist is essential for their long-term survival. 

Despite their body size, tigers are known to be elusive, often moving silently through dense, undergrowth-heavy forests, and this leads to researchers relying on indirect signs such as pawprints (pugmarks) or scat to detect their presence. However, the absence of such signs doesn’t always mean the absence of tigers, but rather that signs went undetected. To combat this issue, scientists use ‘occupancy modelling’, a method that helps distinguish between true absences and non-detections.

Researchers from the Centre for Wildlife Studies and their collaborators applied this approach to the Malenad-Mysore Tiger Landscape of Karnataka, one of India’s most important areas for tiger conservation. The study area, encompassing nearly 38,000 sq km, was divided into 205 square grid cells, each of 188 sq-km each. Field teams walked a total of 4174 km along forest trails, carefully noting every pugmark and scat encountered.

By analysing this data, researchers estimated that tigers occupied 66% of suitable habitats in the region. Without accounting for imperfect detection, this number would have been underestimated at 47%. The study also found that healthy prey populations and well-protected forests were key to tiger presence, while signs of livestock, a marker of human disturbance, were linked to lower tiger occurrence.

Most significantly, these occupancy maps revealed gradients of tiger occurrence, highlighting areas that act as source populations from which tigers can disperse into surrounding habitats. This helps conservationists focus protection and restoration efforts where they are most effective.

Innovative methods such as these help demonstrate how field-based sign surveys, when combined with robust statistical techniques, can provide powerful insights for conservation. They offer a cost-effective, large-scale monitoring tool for wide-ranging species like tigers, and help ensure their survival in the forests of India for generations to come. 

You can access the original article by clicking here.

Keywords: Tiger, Panthera tigris, Occupancy, Western Ghats, Sign Survey, Landscape, Distribution, Occurrence, Monitoring, Conservation