Seasonal variation in gut microbiota of migratory wild raptors: a case study in white-tailed eagles.

Background: Migration poses significant energetic challenges for migratory birds, during which both intrinsic and extrinsic factors affecting the gut microbiota alter substantially. While the temporal dynamics of gut microbiota in wild birds across migration seasons have garnered increasing attention, research on the seasonal variation in wild raptors remains limited despite their distinct gut microbiota structures. Furthermore, raptors, being the highest trophic level in the food chain, have been found to harbor more pathogens and antibiotic resistance genes (ARGs). In this study, we characterized the diversity and composition of the gut microbiota of wild white-tailed eagles at a critical stopover site along the East Asian Flyway (EAF). Fecal samples were collected during both autumn and spring migration seasons and microbial compositions were analyzed using high-throughput sequencing.

Results: The most prevalent bacterial phylum in the gut microbiome of white-tailed eagles during both migration seasons was Firmicutes. The diversity of the gut microbiota is elevated in the spring migration season and the bacterial community composition significantly differed between two seasons. Individuals in spring migration show elevated levels of Clostridium_sensu_stricto_13 and Brochothrix, most likely related to the consumption of carrion. Conversely, individuals in autumn migration showed a higher prevalence of potential pathogens such as Fusobacterium and Escherichia-Shigella. Furthermore, we found that specific genera were seasonally enriched, probably reflecting distinct environmental exposures along migration routes.

Conclusions: This study revealed substantial seasonal variation in the gut microbiota of migratory white-tailed eagles, most likely shaped by dietary shifts, environmental factors, and physiological stress during migration. The higher prevalence of pathogens during autumn migration highlights potential health risks for eagles and their ecosystems, emphasizing the need for targeted conservation strategies at stopover sites. These findings contribute to understanding the dynamic interactions between migration and gut microbiota in wild raptors and provide valuable insights into their ecological and health management. While dietary differences may play a role, further research is needed to directly assess their impact.