The evolution of migration routes in birds remains poorly understood as changes in migration strategies are rarely observed on contemporary timescales.1-3 The Richard's Pipit Anthus richardi, a migratory songbird breeding in Siberian grasslands and wintering in Southeast Asia, has only recently become a regular autumn and winter visitor to western Europe. Here, we examine whether this change in occurrence merely reflects an increase in the number of vagrants, that is, "lost" individuals that likely do not manage to return to their breeding grounds, or represents a new migratory strategy.4-6 We show that Richard's Pipits in southwestern Europe are true migrants: the same marked individuals return to southern France in subsequent winters and geo-localization tracking revealed that they originate from the western edge of the known breeding range. They make an astonishing 6,000 km journey from Central Asia across Eurasia, a very unusual longitudinal westward route among Siberian migratory birds.7,8 Climatic niche modeling using citizen-science bird data suggests that the winter niche suitability has increased in southwestern Europe, which may have led to increased winter survival and eventual successful return journey and reproduction of individuals that initially reached Europe as autumn vagrants. This illustrates that vagrancy may have an underestimated role in the emergence of new migratory routes and adaptation to global change in migratory birds.9,10 Whatever the underlying drivers and mechanisms, it constitutes one of the few documented contemporary changes in migration route, and the first longitudinal shift, in a long-distance migratory bird.
Keywords: Richard’s Pipit; climate change; geolocators; migration route; molt; seasonal migration; vagrancy.
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