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In a ®eld study on the behavioural response of grey-sided voles Clethrionomys rufocanus to predator odour ear tattoos were used for individual marking of the voles in the ®eld. The study was conducted over three summer seasons in the tundra of northern Norway. In this paper we report our experience with eartattooing in order to compare it with other methods used for marking small mammals. Methods should be compared for their different in¯uences on physiology and behaviour and to ®nd alternatives to the widely used toe-clipping. Looking for alternatives becomes mandatory because in many countries this method needs a special permit or is totally prohibited by law. Marking a vole with ear-tattoos took us 2 min on average. The rate for the ®rst recapture after marking voles was 87%. This is much higher than reported recapture rates for toe-clipped voles. From all recaptured individuals we were able to identify > 89.9% of the codes. The time lag between marking and ®rst recapture was higher than the lag between second and third recapture, which indicates a trauma caused by the marking procedure. However, there was no evidence of any weight loss as reported for other marking methods, and most of the tattooed animals did not show any behaviour indicating irritation after being marked. It is concluded that ear-tattooing, as an alternative to other methods of marking small mammals is useful even in the ®eld. However, to assess different advantages and disadvantages in other circumstances, the chosen method should be examined critically before use.

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