Social behaviour is a key determinant of virome diversity in New Zealand passerines
Wild birds are important reservoirs of viral diversity and can play key roles in the emergence and dispersal of infectious diseases. Their ability to harbour multiple infections without overt disease, combined with their mobility and ecological interactions, creates opportunities for viruses to spread across species and geographic regions. Despite this, the factors shaping avian viromes remain poorly understood, particularly in Aotearoa New Zealand, where endemic and introduced bird species coexist within a relatively isolated ecosystem. This study used metatranscriptomic sequencing to characterise the viromes of 443 endemic and introduced passerines sampled over four years within a shared ecological setting. A total of 217 viruses, representing 69 viral species across 14 families, were identified, including 54 previously undescribed viruses. Many were closely related to viruses reported from birds in Asia, North America, Europe and Australia, suggesting historical or ongoing viral exchange through migration, co-divergence or cross-species transmission. Introduced passerines harboured greater viral diversity than endemic species, while social behaviour was a key predictor of virome composition with flocking species exhibiting higher viral richness and diversity than solitary or pair-living taxa. In contrast, non-viral microbial communities were primarily shaped by host species and diet, indicating that viral communities are influenced by ecological processes distinct from those associated with the non-viral microbiome. These findings provide new insight into the ecological and behavioural drivers of avian viral diversity.