Time in camera-trap data, which could help us learn more about the behaviour and movement of tigers, was rarely used. A new model, however, has incorporated the time and location of photo-capture to estimate the abundance and spatial distribution of tigers.
The new methodology is said to be a crucial addition to science-based management for tiger conservation, as 70% of wild tigers are concentrated in less than 6% of remaining habitats worldwide.
The study, ‘A hierarchical model for estimating the spatial distribution and abundance of animals detected by continuous-time recorders’, published in the current issue of the international journal PLoS ONE, was led by Robert Dorazio of the United States Geological Survey, and co-authored by Wildlife Conservation Society Director for Science in Asia, Ullas Karanth.
The scientists illustrated the continuous-time spatial capture-recapture (SCR) model by analysing spatial and temporal patterns evident in the camera-trap (continuous-time recorders) detections of tigers living in and around Nagarahole Tiger Reserve in Karnataka . The new model made full use of location and time of photo-capture data, as opposed to traditional SCR analysis which uses only location of photo-capture data. “Camera trap locations were selected to increase detections using prior knowledge of the behaviour and range of movements of individual tigers. Each camera trap operated continuously during the 45-day period of sampling (26 November 2014 to 13 January 2015), recording the date and time when a tiger was photographed. Individual tigers were identified from photographs using their unique stripe patterns,” the study said.
A total of 86 individual tigers were detected during the period, which included a per-camera average of 21.2 days of daytime and 23.4 days of night time. “Tigers were detected in a total of 355 capture events. Most of these detections occurred during the night time, providing evidence of nocturnal activity patterns of tigers,” said the study.
“We are now able to exactly incorporate the time of capture into the data analysis. This gives us more power to mimic nature in the sense of how tigers actually get ‘trapped’ in cameras, and how their movement, behaviour, and space-use relate to time. This is a significant advance,” Dr. Karanth was quoted as saying.
