Bairlein, F. | bioRxiv Science

bioRxiv2022

Eco-evolutionary drivers of avian migratory connectivity

Understanding how individuals redistribute after migration assists in the conservation and management of mobile species, yet the eco-evolutionary drivers of migratory connectivity remain unclear. Taking advantage of an exceptionally large (~150,000 individuals, 83 species) and more-than-a-century long dataset of bird ringing encounters, we investigated determinants of avian migratory connectivity on both short- and long-distance migrants. Most species exhibited significant connectivity likely due to the large intraspecific variability in migration strategies, which often led to the identification of distinct migratory populations. Migratory connectivity was strongly predicted by geography, especially migration distance, but it was evolutionary labile and weakly influenced by biological traits due to flexibility in migratory behaviour. By unravelling determinants of migratory connectivity we improve knowledge about the resilience of migrants to ecological perturbations. Also, our population-level analysis provides a critical tool to inform transboundary conservation and management strategies by explicitly considering the large intraspecific variability of avian migration.

ecology↗

bioRxiv2022

A magnetic pulse does not affect free-flight navigation behaviour of a medium-distance songbird migrant in spring

Current evidence suggests that migratory animals extract map information from the geomagnetic field for true navigation. The sensory basis underlying this feat is elusive, but presumably involves magnetic particles. A common experimental manipulation procedure consists of pre-treating animals with a magnetic pulse. This aims at re-magnetising particles to alter the internal representation of the external field prior to a navigation task. While pulsing provoked deflected bearings in laboratory experiments, analogous studies with free-flying songbirds yielded inconsistent results. Here, we pulsed European robins (Erithacus rubecula), being medium-distance migrants, at an offshore stopover site during spring migration and monitored their free-flight behaviour with a regional-scale tracking system. We found no pulse effect on departure probability, nocturnal departure timing, or departure direction, in agreement with results on a long-distance migrant released at the same site in autumn. This necessitates a reassessment of the importance of geomagnetic maps for migratory decisions for free-flying birds. Summary statementMagnetic pulse pre-treatment disturbs geomagnetic map usage of birds in lab environments. However, our free-flying birds show no effect, suggesting geomagnetic map information is less important in the natural environment.

animal behavior and cognition↗