One of the tasks of the Post-Release Monitoring (PRM) team involves collecting data on the phenology of natural-occurring plant species in orangutan habitats. While conducting phenological surveys, the BOS rangers occasionally meet orangutans as well. Let’s learn about one of these encounters that occurred during a recent survey in the Kehje Sewen Forest in East Kalimantan!

While trekking along the main route in a special area approximately two hours walk from camp, the team found traces of orangutan foods, such as suli, also known as Etlingera sp. or wild ginger.

Upon arriving at the survey site, the team immediately split into two. The first team moved to an area known as Phenology 2, while the second team went to Phenology 4. After an hour of surveying, the second team heard the sound of rustling branches. At first, the sound was thought to be from a monkey or gibbon. However, not long after, an orangutan appeared. Not afraid of the human’s presence, the female came closer. She climbed down branch by branch from the top of a tree while the team waited vigilantly, preparing to identify her.

Not happy with human intruders

As she approached, the rangers noticed the healthy-looking female was quite large with thick hair. However, her face was unrecognisable. She kiss-squeaked, indicating that she did not appreciate the team’s presence. While she sat on a branch waiting for the human intruders to leave, the PRM team took photos of her face from several angles to later identify her back at camp.

The mysterious female orangutan kept a close eye on the BOS team.

The rangers resumed the phenological survey as initially planned, with the orangutan shadowing them. Even when the terrain revealed an unfavourable descent and the team had to reroute towards the riverbank, the female was still following along. She seemed determined to keep an eye on the humans trespassing in her part of the forest.

Loud noises shoo her away

After waiting some time for the female orangutan to move on, the team grew concerned that she was overly comfortable with humans. Eventually, they decided to shoo her away with loud noises, and by banging the tree trunk she was perched in. Their attempts were successful, as she soon moved off through the high canopy, where she could not disrupt the survey process below.

As soon as all team members completed the survey, they rushed back to the camp to try and identify the mystery orangutan. Through comparisons with other photos, they discovered that the female in question was Erina, who the BOS Foundation team released in 2018. Based on our records, Erina was previously known as a beloved and playful individual.

How delighted the PRM team was to encounter Erina in such good condition after they had last laid eyes on her almost half a year ago!

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