Comparative overview of activity phenology in blackbirds and song thrushes

Every autumn and spring, billions of songbirds undertake migratory flights that only recently became possible to study in these small species, thanks to advances in biologging technology that made loggers light enough to record their activity continuously across the year in the wild. This technology was used to compare how two closely related songbirds, the blackbird (Turdus merula) and the song thrush (Turdus philomelos), organize their activity across the day and year, and how this relates to their different migration strategies and distances, with song thrushes often migrating longer distances than blackbirds. Our results show that song thrushes became substantially more active during migration and shifted much of this activity into the night, at times almost matching their daytime activity. Blackbirds, on the other hand, showed only a small increase in overall activity during migration, but this activity was more sharply concentrated into a handful of especially intense days. Together, these findings suggest that migration distance and strategy shape not just how far and when birds fly, but also how they structure their entire daily and annual cycles.