Conserving bird populations in the Anthropocene: the significance of non-breeding movements

Abstract

ABSTRACTBackgroundTo conserve bird species threatened by climate change, it is important to understand how environmental factors affected by climate change, such as snow cover, impact their ranges. While this problem is fairly well understood for breeding areas, it remains poorly understood for non-breeding areas. In non-breeding areas, seasonal cycles can strongly influence the distribution of resources during winter. If birds adapt to such changes, they may result in seasonal and directional movement of birds within their non-breeding range. In this case, birds would experience a unique migration pattern - rapid migration between breeding and non-breeding habitats versus a slow migration pattern within their non-breeding range. Their non-breeding range would therefore be dynamic, with potentially important consequences for our understanding of population densities and non-breeding ranges.MethodsBetween 2013-2021, we tracked 43 adult Rough-legged buzzards with solar GPS-GSM loggers. We analyzed their behavior, determined whether the birds showed any directional return migrations during the non-breeding season, and evaluated the differences between the slow migration within their winter range and the quick migration between breeding and non-breeding areas. We also analyzed the vegetation cover of the areas crossed during quick and slow migrations and the role of snow cover in winter migrations.ResultsOur findings revealed that after a quick fall migration through the taiga zone, Rough-legged buzzards continue to migrate during the non-breeding season, albeit at a slower pace across the wooded fields they select as habitat. They avoid complete snow cover and move to escape the progression of the snow cover line from northeast to southwest and back during the winter. As a consequence, Rough-legged buzzards have a dynamic winter range. Thus, the migration pattern of these birds comprises alternating quick and slow phases, resembling the foxtrot dance, which we have named the ‘foxtrot’ migration pattern. Due to this pattern, their winter range displays a dynamic shift of the seasonal center of the population distribution over 1000 km towards the southwest and back throughout the winter.ConclusionsOur study uncovered a novel bird migration pattern postulated to exist before but poorly understood. This ‘foxtrot migration’ likely occurs in many migratory species inhabiting winter areas with pronounced seasonal cycles. Our findings have implications for conservation efforts in the Anthropocene, where environmental factors such as snow cover can change rapidly and have cascading effects on bird migration. We recommend presenting dynamic winter ranges in species descriptions and range maps so ecologists can use them to develop effective conservation strategies.