The influence of climate change on the autumn migration timing of three common migratory raptors in East Asia

Many bird species have shown temporal changes in their migration phenology due to global warming. The phenomenon of bird species advancing their spring phenology in response to warmer spring temperatures is well-documented and extensively studied. However, autumn phenology, a crucial component of the migrating birds' annual cycle, has garnered less attention. In contrast to spring phenology, which often exhibits consistent timing changes across the majority of species, the timing of autumn migratory events is subject to greater variability. In this research, we explored the trends in autumn migration and the impact of climate change on these patterns. Our analysis was grounded in a 39-year dataset of bird-banding records from the Changdao Raptor Migration Observatory in China, a key migration bottleneck for East Asian-Australasian Flyway. The dataset encompassed three prevalent migratory raptors: the Oriental Scops Owl (Otus sunia), the Japanese Sparrowhawk (Tachyspiza gularis), and the Eurasian Sparrowhawk (Accipiter nisus). Our analysis showed that the autumn migration timing for these three prevalent raptors has been significantly influenced by climatic changes occurring at both the breeding and stopover sites. The median passage dates for the Oriental Scops Owls and Japanese Sparrowhawks advanced significantly, whereas the Eurasian Sparrowhawks delayed their passage date significantly. The Eastern Atlantic/Western Russia Index, the North Atlantic Oscillation, and the local weather dynamics along the migration route played pivotal roles in shaping the autumn migration timings of the three common raptors. In summary, our findings, based on extensive long-term ringing data, reveal distinct temporal trends in the autumn migration patterns of three small raptors in Asia, highlighting the pivotal climate indices linked to these trends.