This paper reviews the use and the effects of marks and devices on birds. Although most papers reporting research on birds make use of marks or devices, very few studies test for harmful effects or data biases caused by these. Many research projects have used marks and devices without encountering any harmful effects of these on the birds being studied. However, where assessments have been made it is clear that all of the methods of marking can have adverse effects, while most devices attached to birds do alter their behaviour to some extent. We conclude that more attention should be given to these effects before the normal assumption of no influence on the biological parameters being studied can be made with confidence. There is a need for careful tests of the effects of marking methods to be undertaken. We hope that this review will assist people studying birds to plan their use of marks and devices in such a way as to minimize problems caused by these research tools.

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