Rodent pest management and predator communities in oil palm plantations in Indonesia: a comparison of two contrasting systems

Rapid expansion of oil palm cultivation in Southeast Asia raises concerns about biodiversity conservation. Moreover, rats are invasive pests in oil palm plantations, often causing substantial damage. In Indonesia, rat control is generally based on field treatment using anticoagulant rodenticides and/or on reinforcement of predation by barn owls (Tyro alba), by providing nest boxes within the plantation. Rodenticide use is costly for the producer and can indirectly poison non-target species such as rat predators. Thus, biological control of rodent pest s should be promoted, both from a conservation and a production points of view. Within the assemblage of rat predators, small carnivores may contribute to rodent population regulation. However persistence of small carnivores within oil palm plantations, their habitat use, their diet and their contribution to rodent control have been poorly investigated. We conducted a 3-year comparative study (2010 - 2012) in well - established oil palm plantations in Riau and Bangka provinces, in Indonesia: in both areas barn owls have been successfully introduced, but in Riau rat population s have been maintained at an acceptable level without the use of rodenticide for more than 10 years, whereas in Bangka intensive rodenticide application s did not prevent high level s of rat damage. We compared these two contrasted systems in term of predators community (barn owls and small carnivores) abundance and/or diet. Using a kilometric abundance index yielded from spotlight and faeces counts, we found that small carnivores were much more abundant in Riau plantations than in Bangka, and that the leopard cat (Prionailurus bengalensis) was the dominant species in Riau and absent from Bangka. We investigated the diet at community level and found no significant difference s in frequency of occurrence or volume of small mammal's food items in the faece s of small carnivores between Bangka and Riau; however, we found that the importance of vegeta