Capture of Wild Orangutans by Drug Immobilization

Abstract

Drug immobilization was used to address the increasing demand for a safe and reliable method of capturing wild orangutans that remain in remnant forest on agricultural plantations. This paper reports the capture of 70 animals by this means, mostly using a 5:1 ketamine-xylazine mixture at a mean dosage of 8.43 mg for the two drugs combined or 7.03 mg ketamine and 1.41 mg xylazine/kg body weight. An alternative drug used in a few cases was Zoletil (1:1 tiletamine-zolazepam) at a dosage of 6.90 mg/kg. The darting system of choice was the Telinject air-pressure powered vario 4V rifle, with reusable plastic darts activated by compressed air. A Dist-inject N 60 rifle, using either “Speedy” pre-loaded disposable plastic darts or aluminum darts assembled on demand, was used as a back-up. There was a wide range of tolerance to dosage levels, ranging from 2.60 to 22.64 mg/kg, indicating a wide safety margin for this mixture with orangutans. A high degree of individual variability in reaction to the drugs was also encountered and supplementary doses were required to complete immobilization in a large proportion of cases. A standard dosage for the 5:1 ketamine-xylazine mixture of 8 mg/kg estimated body weight is recommended for drug capture of wild orangutans.