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- Data packageData from: Migration of red-backed shrikes from the Iberian Peninsula: optimal or sub-optimal detour?(2017-03-23) Tøttrup, Anders P.; Pedersen, Lykke; Onrubia, Alejandro; Thorup, KasperNOTE: An updated and larger version of this dataset is available. See https://doi.org/10.5441/001/1.4bt7365c. ABSTRACT: The current Northern Hemisphere migration systems are believed to have arisen since the last glaciation. In many cases, birds do not migrate strait from breeding to non-breeding areas but fly via a detour. All western European populations of red-backed shrikes Lanius collurio are assumed to reach their southern African wintering grounds detouring via southeast Europe. Based on theoretical considerations under an optimality framework this detour is apparently optimal. Here, we use individual geolocator data on red-backed shrikes breeding in Spain to show that these birds do indeed detour via southeast Europe en route to southern Africa where they join other European populations of red-backed shrikes and return via a similar route in spring. Disregarding potential wind assistance, the routes taken for the tracked birds in autumn were not optimal compared to crossing the barrier directly. For spring migration the situation was quite different with the detour apparently being optimal. However, when considering potential wind assistance estimated total air distances during autumn migration were overall similar and the barrier crossing shorter along the observed routes. We conclude that considering the potential benefit of wind assistance makes the route via southeast Europe likely to be less risky in autumn. However, it cannot be ruled out that other factors, such as following a historical colonisation route could still be important.
- Data packageData from: Remarkably similar migration patterns between different red-backed shrike populations suggest that migration rather than breeding area phenology determines the annual cycle(2020-10-03) Pedersen, Lykke; Onrubia, Alejandro; Vardanis, Yannis; Barboutis, Christos; Waasdorp, Stef; van Helvert, Monique; Geertsma, Marten; Ekberg, Per; Willemoes, Mikkel; Strandberg, Roine; Matsyna, Ekaterina; Matsyna, Alexander; Klaassen, Raymond H.G.; Alerstam, Thomas; Thorup, Kasper; Tøttrup, Anders P.The regular fluctuation of resources across the Globe guides movements of migratory animals. To ensure sufficient reproductive output and maintain viable population sizes, migratory animals should match arrival at breeding areas with local peaks in resource availability. It is generally assumed that breeding phenology dictates the timing of the annual cycle, but this is poorly studied. Here, we use light‐level geolocator tracking data to compare the annual spatiotemporal migration patterns of a long‐distance migratory songbird, the red‐backed shrike, Lanius collurio, breeding at widely different latitudes within Europe. We find that populations use remarkably similar migration routes and are highly synchronized in time. Additional tracks from populations breeding at the edges of the European range support these similar migration patterns. When comparing timing of breeding and vegetation phenology, as a measure of resource availability across populations, we find that arrival and timing of breeding corresponds to the peak in vegetation greenness at northern latitudes. At lower latitudes birds arrive simultaneously with the more northerly breeding populations, but after the local greenness peak, suggesting that breeding area phenology does not determine the migratory schedule. Rather, timing of migration in red‐backed shrikes may be constrained by events in other parts of the annual cycle.
- Data packageData from: Sex-specific difference in migration schedule as a precursor of protandry in a long-distance migratory bird(2019-08-07) Pedersen, Lykke; Jakobsen, Nina Munkholt; Strandberg, Roine; Thorup, Kasper; Tøttrup, Anders P.NOTE: An updated and larger version of this dataset is available. See https://doi.org/10.5441/001/1.4bt7365c. ABSTRACT: Protandry, the earlier arrival of males at the breeding grounds relative to females, is common in migratory birds. However, due to difficulties in following individual birds on migration, we still lack knowledge about the spatiotemporal origin of protandry during the annual cycle, impeding our understanding of the proximate drivers of this phenomenon. Here, we use full annual cycle tracking data of red-backed shrikes Lanius collurio to investigate the occurrence of sex-related differences in migratory pattern, which could be viewed as precursors (proximate causes) to protandry. We find protandry with males arriving an estimated 8.3 days (SE = 4.1) earlier at the breeding area than females. Furthermore, we find that, averaged across all departure and arrival events throughout the annual cycle, males migrate an estimated 5.3 days earlier than females during spring compared to 0.01 days in autumn. Event-wise estimates suggest that a divergence between male and female migratory schedules is initiated at departure from the main non-breeding area, thousands of kilometres from, and several months prior to arrival at the breeding area. Duration of migration, flight speed during migration and spatial locations of stationary sites were similar between sexes. Our results reveal that protandry might arise from sex-differential migratory schedules emerging at the departure from the main non-breeding area in southern Africa and retained throughout spring migration, supporting the view that sex-differential selection pressure operates during spring migration rather than autumn migration.
- Data packageData from: Full-year tracking suggests endogenous control of migration timing in a long-distance migratory songbird(2018-08-07) Pedersen, Lykke; Jackson, Kayla; Thorup, Kasper; Tøttrup, Anders P.NOTE: An updated and larger version of this dataset is available. See https://doi.org/10.5441/001/1.4bt7365c. ABSTRACT: Following ongoing technological advances, an increasing amount of full-year tracking data on individual migratory movements is becoming available. This opens up the opportunity to study how migration develops within individuals in consecutive years and the extent to which the migratory program is constrained. Such knowledge is essential for understanding the degree of individual flexibility during the annual cycle, which may help identifying potential bottlenecks, where the range of individual decisions is restricted. In this study, we investigate repeatability in time of a long-distance migratory songbird, the red-backed shrike Lanius collurio, tracked across consecutive years (n = 7). Furthermore, we explore the population variability and dependencies between consecutive events of departure and arrival throughout the annual cycle in this species (n = 15). We find that individuals show high repeatability in timing of departure from their two main non-breeding areas in sub-Saharan Africa. In contrast, low repeatability is found in timing of arrivals to stationary sites throughout the annual cycle. Population variation in timing of departure and arrival was similar across all events, ranging from 30 to 41 days, and was highly dependent on timing of preceding events. We conclude that timing of departures is the key event potentially controlled by the individual innate migration program, while arrivals are more flexible, likely dependent on the environmental conditions experienced en route in red-backed shrikes. Still, apparent flexibility in the individual schedule may be hampered by overall constraints of the annual cycle.