This inference came to light in a collaborative study on the sloth bear distribution in Bhadra Tiger Reserve in Karnataka by the Wildlife Conservation Society-India Program, the Centre for Wildlife Studies and the University of Florida-Gainesville.
The researchers believe this finding, published in this edition of the Journal of Applied Ecology, has important implications for wildlife conservation as sign surveys offer a cheaper data source for occupancy models compared to direct detection methods.
The study, based on data from a long-term ecological study of tigers led by Wildlife Conservation Society scientist Ullas Karanth, provides the first rigorous comparison of two methods i.e. sign surveys and camera trap survey to estimate proportion of habitat occupied by the sloth bear.
“The bears, which are solitary animals endemic to southern Asia, were chosen as a study species because they offer clear advantages in ensuring no false positive detections,” an official statement quoting lead author of the paper Arjun Srivathsa as saying.
“Photo-captures of sloth bears and from camera-trap surveys and indirect signs of the species are unmistakable,” he said.
Occupancy estimated from sign surveys of fresh scat and tracks made by sloth bears along forest trails were compared with camera trap captures of bears.
Interestingly, both sources of data produced nearly identical results.
About 57 percent of the area was found to be occupied by sloth bears and this habitat choice was shown to be governed by forest cover and type and terrain ruggedness.
“This study demonstrates the importance of using rigorous statistical methods in surveys of rare and elusive species to optimise the quality of results as well as efficiently use substantial investments being made in such surveys now,a coauthor K. Ullas Karanth said.
Occupancy models are used to assess where the species occur and why and the status of rare and threatened wildlife to guide conservation interventions.
To estimate detection probability, these models can use field data from direct sightings of animals or from camera trap photo “captures”.
Such direct surveys, however, involve greater cost and effort, say the researchers.
Wildlife scientists, therefore, often opt to employ surveys of animal signs such as scat or tracks which are more abundant and easier to find.