Abstract
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.
Highlights
Across the humid tropics, widespread deforestation is dramatically changing habitat and food resource compositions through converting primary forest into mosaic landscapes of mixed agriculture interspersed with patches of remnant forests [1]
As the first temporal study of an isolated orangutan population living in an agroforest system with no periodic access to natural forests, our results indicate that as a coping mechanism orangutans have modified their behaviour to living in a human-dominated landscape
This was illustrated, for example, by orangutans altering their diets as 21% of their total feeding activity budget was on cultivated fruits and by changing their foraging behaviour to raiding crops in the late afternoon or evening, which is when almost all farmers had returned to the village for the night
Summary
Widespread deforestation is dramatically changing habitat and food resource compositions through converting primary forest into mosaic landscapes of mixed agriculture interspersed with patches of remnant forests [1]. Changes in the quality and quantity of food sources, both wild and cultivated, may cause animals to trade-off their activity budgets in different ways Some species, such as olive baboons (Papio anubis), may allocate more time to searching for highly nutritious food patches [6], while other species, such as chimpanzees (Pan troglodytes verus) and green monkeys (Cercopithecus sabaeus), may spend less time searching and more time feeding on larger quantities of less nutritious food [7,8]. These trade-offs will influence time available for other activities, such as defense and reproduction [9], which might influence factors such as reproductive success [10]
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