Absence of differential predation on rats by Malaysian Barn Owls in oil palm plantations

Barn Owls (Tyto alba javanica) have been widely introduced in Malaysian oil palm plantations to control rodent pests. However, their effectiveness in regulating rodent populations is unknown. We investigated whether Barn Owls selected prey with respect to size and sex classes based on data from 128 pellets of Barn Owls compared to 1292 live-trapped rats in an oil palm plantation in Malaysia. The birds mostly fed on Rattus rail as diardii, the most commonly trapped species. Body mass of prey consumed was predicted based on models derived from measurements from trapped rats. Sex of prey was determined by pelvic measurements with reference to those taken from specimens of known gender. There was no clear selection of prey by Barn Owls in relation to size or sex of prey, and no difference in the body mass of prey between the owls' breeding and nonbreeding seasons. The absence of differential predation in Barn Owls may partly explain the lack of dear evidence that they regulate rodent populations and thus act as successful biological control agents

Barn owl predatory behavior and response to prey abundance: towards an ecologically-based agricultural practice

Although Malaysian Barn Owls (Tyto alba javanica) were once considered vagrants, they are now the most common owl species in Malaysia. Their proliferation is largely due to the expansion of agricultural lands in which prey is abundant and nest boxes are made available for them to roost and breed. However, their role in regulating rodent populations is not fully understood and chemical control of rodents is concurrently being used in most plantations leading to other environmental problems including secondary poisoning and bait resistance. This study aimed to detect differential predation and functional and numerical responses of Barn Owls to changes in prey abundances, which are important determinants of effective biological control agents. Over 25,200 trap-nights in an oil palm plantation, a total of 1,292 individual rats were captured; these were mostly Rattus rattus diardii, followed by Rattus argentiventer and Rattus tiomanicus. Based on 203 owl pellets, the birds fed primarily on R. r. diardii, the species that was most frequently trapped. There was no clear selection of prey by Barn Owls with respect to size and sex of prey. There was a significant positive relationship between the relative abundance of rats and the number of owl pellets collected, and higher rat abundances during the owls’ breeding months. This suggests a functional and a numerical response of Barn Owls to changes in prey abundance. Although we found no evidence of differential predation by Barn Owls they did show functional and numerical responses to prey numbers. Hence they could provide successful biological control of rodents and this should be properly accounted in ecologically-based management of the oil palm agroecosystem which would minimize the adverse effects of chemical usage