'SPATIAL MARK-RESIGHT'
STAFF REPORTER
GUWAHATI: Scientists from Aaranyak, Panthera, and WWF-India have developed a model called 'Spatial Mark-Resight' (SMR) to precisely estimate the population size of leopards where the population is a mix of the rosette (common) and melanistic (different) leopards.
"Like the tigers, the leopards can be also individually identified with the help of their unique shape and size of the rosettes that occur across their body coat. However like many other wildlife species, leopards also exhibit phenotypic polymorphism (body colour variation determined by gene). They either have rosettes individuals or melanistic or black individuals commonly called black leopard or Black Panther or Ghong (in Assamese)," explained Dr Firoz Ahmed, Head, Tiger Research and Conservation Division, Aaranyak.
Among the wild cats, melanism has been documented in only 14 out of the 40 species found globally. The melanism presents a unique challenge in estimating and monitoring the leopard population, as it makes the natural marks (rosettes in case of leopard) invisible.
"Our studies have also recorded black leopards in many protected areas in Assam including the 'Manas Tiger Reserve' and the 'Dibru-Saikhowa National Park'. When a population has only rosette-leopard, estimating their population size becomes easy because all the individuals can be identified. Unlike rosette leopards, identification of black leopard individual is sometimes not reliable (special cases exist); therefore, we are unable to completely estimate population sizes of leopards, a metric that is very critical for their conservation," pointed out Dr Ahmed.
This problem is acute in the tropical and subtropical moist forests of south and south-east Asia where the frequency of melanistic leopards is high; and leopards also face the greatest threat. Therefore, previously no precise estimates of leopard population could be done in many protected and non-protected areas in India except on some occasions."The photo-captured images of the leopards from Manas National Park, Assam, India were extracted, rosette leopards were identified individually, and a capture history (putting date, GPS locations, the individual ID of each unique photo-capture of leopard) were prepared by incorporating rosette leopards and melanistic leopards. In the SMR models, we then borrow the capture history information of the rosette leopards and apply that information on the melanistic leopards to estimate the entire population size of leopards," added Dr Ahmed.
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