Although rodenticides have been used successfully for many years for the control of rats in oil palm plantings, interest has been generated recently on the potential of barn owls as agents of biological control. The complexity of this predator-prey system, and logistical difficulties, make the relationships between owl numbers, rat densities and crop damage difficult to study using normal research techniques. In this paper we examine information derived from two alternative study methods: computer modelling and practical field observation. The former shows that the objective of owls moderating rodent populations (i.e. neither eradicating them nor allowing them to increase substantially) may be achieved only under narrowly defined conditions of, initially, relatively low rodent numbers and high barn owl density. When rats are numerous, owls are unable to reduce rodent populations without the aid of some external influence, such as rodenticides. Evidence from field observations is conflicting. On atleast one estate, owls have controlled rats and presumably, their own population has remained viable. On several other estates, as predicted by computer modelling, barn owls are having no measurable impact on high and damaging rat infestations.
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