Estimation of Rehabilitated Sumatran Orangutan Nest Decay Rate (Pongo abelii Lesson 1827) Based on Color and Size at Bukit Tigapuluh National Park Ecosystem (Case Study at Sumatran Orangutan Reintroduction Station, Pengian River, Jambi).

Abstract

In the estimation of orangutan population based on nest density, nest decay rate is used as one of the parameters in calculating site-specific value. Nest decay rate has a site-specific characteristic, which is influenced by several factors, such as altitude, type of forest or habitat, temperature, humidity, and the amount of rainfall. Changes in nest color and size are parameters which can be visibly observed, thus nest color and size can be used as indicators in estimating nest decay rate. The objective of this research was to determine the type of nest that can be used as a reference in estimating orangutan population, analyze nest size in relation to nest decay rate estimation, and analyze nest color in relation to nest decay rate estimation. This research was conducted in July until November 2009 at the Sumatran Orangutan Reintroduction Station, Pengian River, Jambi. Vegetation analysis was done in the forest containing nests used for observation. The method used in the research is Ad libitum. Observations were done to 37 nests, consisting of 25 sleep nests and 12 rest nests. Data collecting for each observed nest was done with an interval of one day. The results show that sleep nests are made by orangutans of all ages. Therefore, sleep nests are the type of nest used as reference in the estimation of orangutan populations. For changes in nest size, significant changes of rest nests occurred on days 1 to 3, 3 to 5, 5 to 12, and 12 to 29. From day 29 until the end of the observation, no significant changes occurred. For sleep nests, significant changes occurred on days 1 to 2, 2 to 4, 4 to 7, 7 to 14, 14 to 21, and 21 to 48. No significant changes occurred from day 48 until the last day of observation. Meanwhile, for changes in nest color, significant changes occurred on days 0 to 1, 1 to 6, 6 to 11, 11 to 13, 13 to 14, 14 to 17, 17 to 25, 25 to 36, 36 to 37, 37 to 50, 50 to 51, 51 to 52, 52 to 59, 59 to 62, 62 to 64, 64 to 69, 69 to 70, 70 to 74, 74 to 77, and 77 to 82. Significant changes in size and color of the orangutan nests occurred through several stages, where each stage requires more time to change compared to its previous stages. This tendency is due to the decaying of the nest during early stages that happen more quickly, causing a longer period for changes to occur during the later stage of the nest. By acknowledging the significant changes that occurred in nest size and color, the estimation of orangutan population by estimating the nest decay rate can be done through the observation of changes in nest color and size.