Java, a popular tourist destination, is experiencing a new spate of killings of endangered javan and pangolin species.
Javan and other species in the region have become targets of illegal poaching, but authorities in Java are struggling to stem the flow of illegal wildlife.
Jaws and other threats have made poaching of endangered animals difficult to stop, officials said.
Last week, an illegal poacher killed two local javan calves in an effort to extort money from a buyer, police said.
The two calves were killed in the area of the town of Pangolin in the Central Java province of Pahang.
The illegal poaching comes as the world is mourning the death of Cecil the lion, who was shot dead by a hunter in Zimbabwe last week.
The poacher in Pangulin reportedly killed the calf in a bid to extorting money from the buyer.
In a press conference, the police chief said the two calves had been killed in an illegal poaching attempt in which the buyer was a foreigner.
The local Javan population in the Java region is estimated at between 15,000 and 20,000.