15-26 November 2010
Location: Bukit Tigapuluh, Sumatra, Indonesia
Perth Zoo Field Worker: Leif Cocks (Curator Exotic section)
When rehabilitated orangutans are released into the rainforest of the Bukit Tigapuluh ecosystem, they can be difficult to track in the thick foliage. Now a trial of new radio transmitters, funded by Perth Zoo, is showing that technology can be an important tool in the reintroduction of Sumatran Orangutans into the wild.
Since 2002, more than 140 Sumatran Orangutans have been released into the Bukit Tigapuluh ecosystem in Sumatra, Indonesia. Their release is part of an international program to reintroduce rescued ex-pet and orphaned orangutans into the wild to establish a new population of this critically endangered species. The program is run by the Frankfurt Zoological Society with support from Perth Zoo, the Indonesian Government and the Australian Orangutan Project.
In September last year, Perth Zoo’s Senior Veterinarian Dr Simone Vitali and Primate Supervisor Clare Campbell travelled to Bukit Tigapuluh to surgically implant radio transmitters under the skin of six orangutans. The transmitters are about the size of a 20 cent coin.
In November, Perth Zoo’s head orangutan keeper Kylie Bullo and I returned to Bukit Tigapuluh to oversee the first trial of the transmitters and see how effective they were in tracking the orangutans. The trial began on 20 November using an antenna and receiver to pick up individual signals (each transmitter has its own frequency). Three of the orangutans with the transmitter implants had been released when we arrived at Bukit Tigapuluh with the other three due to be released in December.
At the start of the day, we visited Mamut, who was one of the orangutans still in the holding complex, to check the receivers were picking up his signal. When we were within 20 metres of him, the signal was very strong and loud, registering the maximum strength of 98 on the receiver. The lowest signal strength (20) registered when the orangutan was about 500 metres away so we were getting a reasonably good range.
After checking everything was working as it should, we set out to find Sahkdia who had been released three weeks earlier but sighted regularly. A short hour later we found her. Sahkdia was about 15 metres up in the canopy foraging for fruit. She had been doing very well since her release and looked to be in excellent condition. We then switched the receiver to pick up Mamut’s signal and successfully navigated our way back to him. Two hours later, we set the receiver on Sakhdia again and found her once more. She had moved about 500 metres since the morning.
The next day we really had to work hard as we were attempting to locate a sub-adult male orangutan named Abel that had not been followed for three days. Abel’s last known location was a one-and-a-half hour walk from the release station. Once there, we turned on the receiver which picked up…nothing. It took us some time scrambling up hills and waving the antenna around before we picked up the signal. The strength of the signal increased significantly as we moved in his direction.
Four-and-a-half hours later, we reached his location. We had to move off the trails and head into the thick rainforest understorey full of leeches, prickly vines and bees. A machete to help clear our path would have been beneficial. We won’t make the mistake of leaving home without one again. Once in his general vicinity, it became apparent he wasn’t going to make himself known. When you re within 20 metres of the orangutan, the signal is at its strongest so at this range you need to rely on your own eyes to find the animal.
Though they have orange hair, orangutans are adept at making themselves invisible. In a rainforest, there are a number of canopy levels so trying to spot an orangutan sitting on one branch of many is tough. After fifteen minutes of craning our necks skywards, one of our team finally shouted out they’d spotted him and we could relax. After watching him for one hour, it was then another couple of
hours back to the station.
With the transmitter trial considered a success, we were now able to focus on other things at the station including behavioural enrichment development and teaching the station’s veterinarian how to use orangutan dental and measurement charts to predict an orangutan’s age. We also visited the local school to deliver coloured pencils and textas donated by Texta to the Australian Orangutan Project, as well as books, toys and puzzles donated by Perth Zoo.
In the future, many more orangutans will have transmitters inserted under their skin prior to their release to make tracking easier.
Perth Zoo supports the conservation of the Bukit Tigapuluh ecosystem which is home to the critically endangered Sumatran Orangutan, Sumatran Tiger and Sumatran Elephant. To help this work continue, please donate to the Zoo’s fundraising program, Wildlife Conservation Action.
