The 958 square km-ATR covers six forest ranges such as Pollachi, Udumalpet, Valparai, Topslip, Amaravathi and Manampalli, official sources said.
The first day of the three-day census will be that of carnivores like Tiger, which will be calculated by their pug marks on the ground and nail marks on trees. Census on the other three days will be for other animals and birds, they said.
The report of the census, which is expected to conclude on May 30, will be submitted to the District Forest Officer, the sources said.