Apes in Space: Saving an Imperilled Orangutan Population in Sumatra

Deforestation rates in Sumatra are amongst the highest in the tropics. Lowland forests, which support the highest densities of orangutans, are particularly vulnerable to clearance and fragmentation because they are highly accessible. Consequently, many orangutans will, in the future, live in strictly or partially isolated populations. Whilst orangutans have been extensively studied in primary forests, their response to living in human-dominated landscapes remains poorly known, despite it being essential for their future management. Here, we focus on an isolated group of critically endangered Sumatran orangutans (Pongo abelii) that co-exist with farmers in a mixed agroforest system consisting of degraded natural forest, smallholder (predominantly rubber) farms and oil palm plantations. Over 24 months we conducted the first ever spatial assessment of orangutan habitat use in the human-transformed landscape of Batang Serangan, North Sumatra. From 1,204 independent crop-raiding incidents recorded, orangutans showed strong foraging preference for mixed farmland/degraded forest habitat over oil palm patches. The core home range areas of the eight adult orangutans encompassed only 14% of the available study area. Monthly home range sizes averaged 423 ha (±139, SD) for males, and 131±46 ha for females, and were positively influenced by wild and cultivated fruit presence, and by crop consumption. The average daily distance travelled was similar for both adult males (868 m±350, SD) and females (866 m±195), but increased when orangutans raided crops. These findings show that orangutans can survive, demographically, in certain types of degraded landscapes, foraging on a mixture of crops and wild fruits. However, the poor quality habitat offered to orangutans by oil palm plantations, in terms of low food availability and as a barrier to female movements, is cause for concern since this is the land use type that is most rapidly replacing the preferred forest habitat across both Sumatran and Bornean orangutan ranges

Raiders of the Lost Bark: Orangutan Foraging Strategies in a Degraded Landscape

Deforestation is rapidly transforming primary forests across the tropics into human-dominated landscapes. Consequently, conservationists need to understand how different taxa respond and adapt to these changes in order to develop appropriate management strategies. Our two year study seeks to determine how wild Sumatran orangutans (Pongo abelii) adapt to living in an isolated agroforest landscape by investigating the sex of crop-raiders related to population demographics, and their temporal variations in feeding behaviour and dietary composition. From focal animal sampling we found that nine identified females raided cultivated fruits more than the four males. Seasonal adaptations were shown through orangutan feeding habits that shifted from being predominantly fruit-based (56% of the total feeding time, then 22% on bark) to the fallback food of bark (44%, then 35% on fruits), when key cultivated resources such as jackfruit (Artocarpus integer), were unavailable. Cultivated fruits were mostly consumed in the afternoon and evening, when farmers had returned home. The finding that females take greater crop-raiding risks than males differs from previous human-primate conflict studies, probably because of the low risks associated (as farmers rarely retaliated) and low intraspecific competition between males. Thus, the behavioral ecology of orangutans living in this human-dominated landscape differs markedly from that in primary forest, where orangutans have a strictly wild food diet, even where primary rainforests directly borders farmland. The importance of wild food availability was clearly illustrated in this study with 21% of the total orangutan feeding time being allocated to feeding on cultivated fruits. As forests are increasingly converted to cultivation, humans and orangutans are predicted to come into conflict more frequently. This study reveals orangutan adaptations for coexisting with humans, e.g. changes in temporal foraging patterns, which should be used for guiding the development of specific human-wildlife conflict mitigation strategies to lessen future crop-raiding and conflicts

Best logistic regression models explaining the relationship between habitat use and the presence or absence of crop-raiding by orangutans.

<p>2log likelihood is the overall fit of each model, <i>K</i> is the number of parameters in each model, ΔAIC is the measurement of each model relative to the top ranked model, and w<i>_i</i> is the AIC model weight.</p

Orangutan home range size estimates (in ha) from Borneo (B) and Sumatra (S) using minimum convex polygon method.

<p>Data table adapted from Singelton et al., 2009 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0017210#pone.0017210-Singleton3" target="_blank">[52]</a> and Utami et al., 2009 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0017210#pone.0017210-UtamiAtmoko1" target="_blank">[34]</a>.</p><p>1, Ketambe orangutan project Universitas Nasional Jakarta & Utrecht University Netherlands;</p><p>2, Ancrenaz and James;</p><p>3, Tuanan orangutan project Universitas Nasional Jakarta & University of Zürich;</p><p>4, Morrogh-Bernard.</p

Orangutan home range (HR) size estimates (in ha) during crop-raiding (CR) and non crop-raiding (NCR) periods using minimum convex polygon (MCP), 100×100 m grid-cell based and Kernel Density Estimation (KDE) methods, and mean daily journey length (MDJ, in m; ±SD) and mean daily linear distance (MLD, in m; ±SD).

<p>* CR: during days when orangutans were recorded to raid cultivated crops, NCR: days orangutans were recorded to eat wild fruits only (i.e. not crop-raiding).</p><p>MDJ and MLD are based on full day follows (n = 157 days).</p