Fluctuations in the Common Vole cycle were indirectly assessed by analysing the contents of Longeared Owl Asia otus pellets in central Drenthe in 1987-97. Although an obligate predator of Common Voles, the proportion of Common Voles in the diet of Long-eared Owls did not reliably depict ups and downs in vole populations (Fig. 1), because variations in the abundance of other small mammals (notably Wood Mouse Apodemus sylvaticus) partly obscured trends in voles. However, troughs in vole populations were apparent in the proportion of birds in the diet of Long-eared Owls, birds constituting the last food resort during a low in vole and mice populations. Therefore, troughs in vole populations are more reliably monitored with the vole-quotient, i.e. the proportion of Microtus arvalis divided by the proportion of birds (+1) in Long-eared Owl pellets (Fig. 1 and 2).