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.