Results of bird ringing in the study of migration routes

Initiated by Hans Christian Cornelius Mortensen in 1899, the ringing of birds unveiled some of the mysteries of avian migrations, notably routes and destinations in migratory species. Using a few case studies, the paper presents an overview about the evaluation of migration routes. It exemplifies how recoveries of ringed birds were used to delineate the species and population specific migration routes, differences in migratory behaviour between sexes and age groups. Ringing also played a significant role in orientation and navigational studies, and it helped to illuminate micro-evolutionary aspects in avian migration. However, the analysis of recovery data is affected by considerable biases and pitfalls owing to variation of reporting rates in space and time. Proper statistical models are needed to analyse movement patterns and their variations. Recently, new tools such as satellite telemetry emerge enabling more sophisticated studies of migration. Nevertheless, ringing of birds continues as a unique and essential method, even for migration studies. More than ever before, however, ringing in bird migration studies requires international collaboration and co-ordinated continent-wide and long-term studies both for basic science as well as for the effective protection of migratory birds.