The Javan Langur Population on the Slopes of Mount Arjuna Has Declined Drastically

PROFAUNA Indonesia's forest and wildlife monitoring team recorded nine groups of Javan langurs (Trachypithecus auratus) on the slopes of Mount Arjuna in the Batu and Karangploso areas throughout 2025. A total of 54 individuals were observed between January and December 2025.

Ten of the Javan langurs observed in 2025 were juveniles. These juveniles are characterized by their orange or golden-yellow hair. Although orange adults are also present, their population is much smaller than the black ones.

Monitoring of Javan langurs on the slopes of Mount Arjuna was conducted in the forests on the Batu and Karangploso sides of Malang Regency. These Javan langurs are found in heterogeneous, well-maintained forests at elevations of 1,000 to 1,700 meters above sea level.

Overall, the forests on Mount Arjuna are located in four regencies: Pasuruan, Mojokerto, Malang, and Batu. The 2025 monitoring focused on the forests bordering Batu and Malang.

The discovery of nine groups of Javan langurs indicates a worrying population decline. A rapid survey by PROFAUNA at the same location in 2005 revealed at least 20 groups of Javan langurs on the slopes of Mount Arjuna.

"The conversion of forest to agricultural land has triggered the decline in the Javan langur population in Arjuna. Many areas that were once forest are now agricultural fields," said PROFAUNA ecologist Rosek Nursahid.

The rampant poaching of Javan langurs from the early 2000s to 2015 also contributed to the decline in the Javan langur population. Javan langurs are hunted for their meat for consumption. Javan langurs are a protected primate species, so they cannot be traded or hunted. Violators face a minimum prison sentence of three years and a maximum of 15 years (Law No. 32 of 2024).

Despite being protected, the Javan langur is under serious threat from habitat loss due to the conversion of forests to agricultural land. Javan langurs generally live in lowland forests and mountainous areas up to 3,000 meters above sea level.

"The Javan langur is a keystone species and a bioindicator of forest sustainability in Java. All parties should be more serious about protecting the forests that serve as the Javan langur's habitat," stressed Rosek Nursahid.