Captivity reshapes the gut microbiome and enriches for antibiotic resistance genes in the oriental pied hornbill

The gut microbiome is essential for host nutrition, immunity, and environmental adaptation, yet its response to captivity in wild birds remains poorly understood. Using shotgun metagenomic sequencing, we compared fecal microbiomes from wild, zoo-housed, and rescue-rehabilitated Oriental Pied Hornbills ( Anthracoceros albirostris ). Wild birds showed the highest alpha diversity, zoo-housed birds the lowest, and rescue-rehabilitated birds an intermediate pattern. Taxonomic, functional, and resistome analyses revealed distinct group-specific profiles. Wild birds were enriched in Lactobacillus , Enterococcus , and Akkermansia , whereas managed birds showed higher abundances of Streptococcus , Weissella , Clostridium , and Ruminococcus . KEGG pathways and ARG classes also differed among groups. These findings indicate that zoo housing and rescue rehabilitation reshape the gut microbiome and resistome of Oriental Pied Hornbills.